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Global and Regional Sea Level Variability and Change
Palma de Mallorca, June 10-12, 2015
Book of abstracts
GLOBAL AND REGIONAL SEA LEVEL VARIABILITY AND CHANGE
Palma de Mallorca, June 10-12, 2015
Global and Regional Sea Level Variability and Change
Palma de Mallorca, June 10-12, 2015
Contents
Keynotes speakers ................................................................................................................................... 9
Sea-level changes during past centuries reconstructed from salt-marsh sediments. Prof. Roland
Gehrels, University of York, UK ............................................................................................................ 9
Considering vertical land motion in understanding sea level change. Prof. Guy Woppelmann,
University of La Rochelle, France ......................................................................................................... 9
The time-mean ocean dynamic topography: How well can we measure, model, and understand it?.
Prof. Chris W. Hughes, National Oceanography Centre, UK .............................................................. 10
What are the challenges facing quantifying impacts and adapting to global sea-level rise?. Dr. Sally
Brown, University of Southampton, UK ............................................................................................. 10
Semi-empirical modelling of sea-level change. Prof. Stefan Rahmstorf, Postdam University, Germany
........................................................................................................................................................... 11
Tide gauge reconstructions and the separation of regional and global mean sea level signals. Prof.
Mark Merrifield, University of Hawaii, USA ....................................................................................... 11
Sea level variability: from surface gravity waves to mean sea level. Prof. Charitha Pattiaratchi,
University of Western Australia, Australia......................................................................................... 12
Modelling historical and future mean sea level change. Prof. Jonathan Gregory, University of
Reading, UK ........................................................................................................................................ 12
Status and challenges on sea level monitoring and forecasting in the Mediterranean Dr. Begoña
Pérez Gómez, Puertos del Estado, Spain ............................................................................................ 13
Paleo Sea Level....................................................................................................................................... 14
Oral Presentations ............................................................................................................................. 14
Holocene relative sea level changes in the Baltic Sea basin: syntheses of geological and
archaeological data. Alar Rosentau .............................................................................................. 14
Sea-level changes in the western Mediterranean during the last 12,000 years: a tool to better
constrain the future projection of sea-level rise. Matteo Vacchi, Nick Marriner, Christophe
Morhange, Giorgio Spada, Alessandro Fontana, Alessio Rovere ................................................... 14
Late Holocene sea-level change in the Falkland Islands: testing the Greenland melt hypothesis.
Newton, T. L., Gehrels, W. R., Daley, T.J., Blake, W. ...................................................................... 15
Posters ............................................................................................................................................... 15
Decoding sea level changes during the MIS 5 by means of Phreatic Overgrowths on Speleothems
(POS) research in coastal caves of Mallorca (western Mediterranean). Joan J. Fornós, Àngel Ginés,
Joaquín Ginés, Francesc Gràcia, Yemane Asmeron, Bogdan P. Onac, Victor Polyak, Paola Tuccimei
....................................................................................................................................................... 15
Sea-level highstands in Mallorca during the last interglacial. Thomas Lorscheid, Paolo Stocchi,
Alessio Rovere, Lluís Gómez-Pujol, Bas de Boer, Thomas Mann, Hildegard Westphal, Joan J. Fornós
....................................................................................................................................................... 16
Vertical Land Movements ...................................................................................................................... 16
Oral Presentations ............................................................................................................................. 16
Global and Regional Sea Level Variability and Change
Palma de Mallorca, June 10-12, 2015
Combination Results of the Tide Gauge Benchmark Monitoring (TIGA) Analysis Centre Reprocessing Products. Addisu Hunegnaw, Norman Teferle............................................................. 16
Models of land uplift in northern Europe. Holger Steffen ............................................................. 17
Relative sea level history during the Holocene and models of the glacial isostatic adjustment
process: constraints from the regions of forebulge collapse. Keven Roy, W.R. Peltier ................. 17
Posters ............................................................................................................................................... 18
Updated GPS vertical velocity field at tide gauges: application to global and regional sea level
change. Médéric Gravelle, Alvaro Santamaria-Gomez, Marta Marcos, Phil Thompson, Guy
Wöppelmann.................................................................................................................................. 18
Using InSAR to monitor vertical ground motions in coastal cities. G. Le Cozannet, D. Raucoules, G.
Wöppelmann.................................................................................................................................. 18
Vertical land movements from the combined use of satellite altimetry and tide gauges. Marta
Marcos, Guy Wöppelmann ............................................................................................................ 19
GNSS reflectometry for tide gauge levelling. Alvaro Santamaría-Gómez, Christopher Watson,
Médéric Gravelle, Matt King, Guy Wöppelmann ........................................................................... 19
Leveling for the altimetric control of tide gauge sensors and GNSS permanent stations in
Barcelona’s and Ibiza’s ports. Tapia Gómez, A; López Bravo, R; Gili Ripoll JA; Martínez Benjamín,
JJ; Pros LLavador, F; Palau Teixidò, V ............................................................................................. 19
A New Datum-Controlled Tide Gauge Record for Sea Level Studies in the South Atlantic Ocean:
King Edward Point, South Georgia Island. Norman Teferle, Addisu Hunegnaw, Philip Woodworth,
Peter Foden, Simon Williams, Jeffrey Pugh, Angela Hibbert.......................................................... 20
Mean Sea Level Observations and Processes ........................................................................................ 21
Oral Presentations ............................................................................................................................. 21
The GOCE geoid in support to sea level analysis. Thomas Gruber ................................................ 21
On the decadal trend of global mean sea level and its implication on ocean heat content change.
Lee-Lueng Fu .................................................................................................................................. 21
Deep-ocean contribution to sea level and energy budget not detectable over the past decade. W.
Llovel, J. K.Willis, F.W. Landerer, I. Fukumori ................................................................................. 22
Synchronization of sea level to oceanic and atmospheric forcing. Francisco M. Calafat.............. 22
Annual sea level variability of the coastal ocean: the Baltic Sea-North Sea transition zone. Marcello
Passaro, Paolo Cipollini, Jerome Benveniste .................................................................................. 22
A probabilistic reassessment of 20th century global mean sea level. Carling Hay, Eric Morrow,
Robert E. Kopp, Jerry X. Mitrovica .................................................................................................. 23
Considerations for Estimating the 20th Century Trend in Global Mean Sea Level. Philip R.
Thompson, Benjamin D. Hamlington ............................................................................................. 23
Detecting sea level seasonality in the northwestern Pacific. Xiangbo Feng, M. N. Tsimplis, M.
Marcos and F. M. Calafat............................................................................................................... 24
Detection and attribution of global mean thermosteric sea level change. Aimée B. A. Slangen, John
A. Church, Xuebin Zhang, Didier Monselesan ................................................................................ 24
Global and Regional Sea Level Variability and Change
Palma de Mallorca, June 10-12, 2015
Detecting anthropogenic footprints in sea level rise. Sönke Dangendorf, Marta Marcos, Alfred
Müller, Eduardo Zorita, Jürgen Jensen ........................................................................................... 25
Posters ............................................................................................................................................... 25
Regional Sea Level change in the North Sea since 1900. Frauke Albrecht, Saskia Esselborn, Ralf
Weisse ............................................................................................................................................ 25
Sea level trends and long-term variability in the South China Sea. A.M. Amiruddin, I.D. Haigh, M.N.
Tsimplis, F.M. Calafat and S. Dangendorf ...................................................................................... 26
Altimetric sea level variation and reconstruction in the Arctic. Ole B. Andersen, P. Limkilde
Svendsen, A. Aasbjerg and P. Knudsen .......................................................................................... 26
On the causes of the differential mean sea level variations between the northern and southern
hemispheres of the Earth. Yuri Barkin, José M. Ferrándiz, Isabel Vigo, David García .................. 27
Sea level reconstruction from satellite altimetry and tide gauges using advanced signal
decomposition techniques. Sandra-Esther Brunnabend, Jürgen Kusche, Roelof Rietbroek, and
Ehsan Forootan .............................................................................................................................. 27
Quality control and validation of the new IOP and GOP ocean products from CryoSat-2. Francisco
M. Calafat, Paolo Cipollini, Helen Snaith, Jérôme Bouffard, Pierre Féménias, Tommaso Parrinello
....................................................................................................................................................... 28
Coastal sea level measurements and trends from improved satellite altimetry. Paolo Cipollini,
Francisco M. Calafat, David Cotton, Marcello Passaro, Helen Snaith ........................................... 28
Impact of large-scale climate patterns on sea-level variability in the Gulf of Guinea with focus on
Ghana. Evadzi, P., Hünicke, B., Zorita, E......................................................................................... 29
Variation of sea level and net water flux in the Mediterranean Sea. Luciana Fenoglio-Marc ...... 29
Time-varying trends in regional sea level from tide gauge data. Thomas Frederikse, Riccardo Riva,
Cornelis Slobbe, Taco Broerse, Martin Verlaan.............................................................................. 30
Scientific roadmap towards height system unification with GOCE. Th. Gruber, R. Rummel, M.
Sideris, E. Rangelova, P. Woodworth, C. Hughes, J. Ihde, G. Liebsch, A. Rülke, Ch. Gerlach, R.
Haagmans ...................................................................................................................................... 30
The Various of Wet Tropospheric Corrections effect on the Regional Sea Level Variability in the
Indonesia Seas. Eko Yuli Handoko, Maria Joana Fernandes, Clara Lazaro .................................... 31
Ocean Bottom Pressure Records at the Permanent Service for Mean Sea Level. Angela Hibbert,
Andrew Matthews, Chris W. Hughes, Mark E. Tamisiea ............................................................... 31
The Semiannual Oscillation of Southern Ocean Sea Level. Angela Hibbert, Harry Leach, Phil
Woodworth .................................................................................................................................... 31
Celebrating 30 Years of the South Atlantic Tide Gauge Network. Angela Hibbert, Pete Foden, Jeff
Pugh, Geoff Hargreaves, Steve Mack, Phil Woodworth................................................................. 32
Observed changes and variability of mean sea-level in the Baltic Sea region during the last 200
years –a review. Birgit Hünicke,l Eduardo Zorita ........................................................................... 32
Variability of decadal sea-level trends in the Baltic Sea. Sitar Karabil, Eduardo Zorita, Birgit
Huenicke ......................................................................................................................................... 33
Global and Regional Sea Level Variability and Change
Palma de Mallorca, June 10-12, 2015
Forcing of Global Mean Sea Level Interannual variability for the period 1950-2010. Gabriel Jordà,
Francisco Mir Calafat, Mikis Tsimplis ............................................................................................. 33
Nordic Sea Level – Analysis of PSMSL RLR Tide Gauge data. Per Knudsen, Ole Andersen, Carlo
Sørensen......................................................................................................................................... 34
Variability of the ocean bottom pressure along the Gulf of Cadiz and its effect on the sea level
spatial distribution. Irene Laiz, Marta Marcos, Jesús Gómez-Enri, Evan Mason, Begoña Tejedor,
Alazne Aboitiz, Pilar Villares........................................................................................................... 34
Satellite altimetry Calibration/Validation at the Australian Bass Strait site in the context of the
new missions Jason-3 and Sentinel-3. Legresy B., C. Watson, J. Church, N. White, J. Beardsley, J.
Andrewartha .................................................................................................................................. 34
Sensitivity of sea-level rise reconstruction from 1900 to present. Legresy B. , J. Church , N. White,
D. Monselesan and A. Slangen ....................................................................................................... 35
Relative sea-level change along the Italian coast during the late Holocene and projections for
2100: Coastal plain impacts based on high-resolution DTMs and geodetic data. Valeria Lo Presti.,
Fabrizio Antonioli , Alessandro Amorosi , Marco Anzidei , Gianni De Falco , Alessandro Fontana ,
Giuseppe Fontolan , Giuseppe Mastronuzzi , Enrico Serpelloni , Antonio Vecchio ........................ 35
Sea Level Oscillations in The Baltic Sea: From Minutes to Centuries. Igor P. Medvedev, Alexander
B. Rabinovich, Evgueni A. Kulikov .................................................................................................. 36
Tides in the Baltic, Black and Caspian Seas. Igor P. Medvedev, Alexander B. Rabinovich, Evgueni A.
Kulikov ............................................................................................................................................ 36
Comparing coastal and open ocean sea level variability and trend from altimetric data. A. Melet,
M. Nonti, B. Chide, B. Meyssignac, F. Birol .................................................................................... 36
Global and Regional Sea Level Change Over the 20th Century: How Can it Inform Us About the
21st Century?. R. S. Nerem, B. D. Hamlington, F. Landerer, R. Leben, and J. Willis....................... 37
Global Sea Level rise from an Empirical Mode Decomposition perspective. Marco Olivieri, Giorgio
Spada, Gaia Galassi........................................................................................................................ 37
The Annual Global-Mean Thermosteric Height Budget. Christopher G. Piecuch, Rui M. Ponte .... 38
Deriving sea level from tide gauges. Jens Schröter, Manfred Wenzel, Klaus Grosfeld, Roelof
Rietbroek ........................................................................................................................................ 38
The South Atlantic sea level variability. Raisa de Siqueira Alves, Angela Hibbert and Harry Leach
....................................................................................................................................................... 38
Closing the gap between regional and global sea level in the Bay of Bengal. Bernd Uebbing, Roelof
Rietbroek, Sandra-Esther Brunnabend, Jürgen Kusche .................................................................. 39
How long does it take to measure a trend in ocean bottom pressure?. Joanne Williams, Chris
Hughes, Mark Tamisiea ................................................................................................................. 39
Modelling Sea Level Changes ................................................................................................................. 40
Oral Presentations ............................................................................................................................. 40
Long-Term Internal Variability Effects on Centennial Dynamic Sea Level Projections. Mohammad
H. Bordbar Thomas Martin, Mojib Latif, Wonsun Park.................................................................. 40
Global and Regional Sea Level Variability and Change
Palma de Mallorca, June 10-12, 2015
Interannual Predictability of North Atlantic Sea Level Dynamics. Robert Fraser, Laure Zanna, Chris
Wilson ............................................................................................................................................ 40
Seasonal coastal sea-level prediction using a dynamical model. John A. Church, Peter C. McIntosh,
Elaine R. Miles, Ken Ridgway, Claire M. Spillman .......................................................................... 41
Regional Budgets of Sea Level in the ECCO-Production Release 1 Ocean State Estimate.
Christopher G. Piecuch, Rui M. Ponte, Gael Forget, Ichiro Fukumori ............................................. 41
Imprints of oceanic intrinsic variability on altimetric measurements: an OGCM study. Guillaume
Sérazin, Thierry Penduff, Laurent Terray, Bernard Barnier, Jean-Marc Molines ........................... 42
A near-uniform fluctuation dominating sea level and ocean bottom pressure variations across the
Arctic Ocean and the Nordic Seas. Ichiro Fukumori, Ou Wang, William Llovel, Ian Fenty, Gael
Forget ............................................................................................................................................. 42
Pacific sea level trends: internally or externally forced? Felix Landerer ....................................... 42
Spatial scales and the detection of externally forced signals in regional sea surface height in CMIP5
models. Kristin Richter, Ben Marzeion ........................................................................................... 43
Worst-case scenarios for sea level rise from ice sheet melt. Carmen Boening, Nicole Schlegel,
Michael Schodlok, Daniel Limonadi, Eric Larour, Michael M. Watkins .......................................... 43
Asymmetry in regional sea level rise projections due to skewed ice sheet contributions. Renske de
Winter, Thomas Reerink and Roderik van de Wal ......................................................................... 44
Posters ............................................................................................................................................... 44
Analysis of the regional pattern of sea level change due to ocean dynamics and density change
for 1993–2099 in observations and CMIP5 AOGCMs. Roberto A. F. Bilbao, Jonathan M. Gregory,
Nathaelle Bouttes .......................................................................................................................... 44
Global reconstructed daily storm surge levels from the 20th century reanalysis (1871-2010). Alba
Cid, Paula Camus, Sonia Castanedo, Fernando Méndez, Raúl Medina ......................................... 45
Nonlinear model of the long-term sea-level fluctuations in the Caspian Sea. Anatoly V. Frolov . 45
Sea Level Complexity in Observations And Models. M. Karpytchev, M. Becker, M. Marcos, S.
Jevrejeva, S. Lennartz-Sassinek ...................................................................................................... 46
Explaining the spread of CMIP5 climate models in global-mean thermosteric sea level rise over
the 20th and 21st centuries. B. Meyssignac, A. Melet .................................................................. 46
Multi-annual predictability of regional sea level in a global climate model. C. D. Roberts, N.
Dunstone. L. Hermanson, M. Palmer, D. Smith .............................................................................. 47
Statistical modeling of Sea Level for regional semi-enclosed basins. Luca Scarascia and Piero
Lionello ........................................................................................................................................... 47
Projections of 21st Century Sea Level Changes for Norway. Matthew J. R. Simpson, J. Even Ø.
Nilsen, Oda Ravndal, Kristian Breili, Halfdan P. Kierulf, Holger Steffen, Eystein Jansen, Hilde Sande,
Mark Carson ................................................................................................................................... 48
Sea surface height variability in the North East Atlantic from satellite altimetry. Paul Sterlini, Hylke
de Vries and Caroline Katsman ...................................................................................................... 48
Global and Regional Sea Level Variability and Change
Palma de Mallorca, June 10-12, 2015
What is the most robust time series analysis tool to isolate mean sea level from tide gauge
records?. Phil Watson .................................................................................................................... 49
Regional evaluation of surface mass balance forcing of an ice flow model for the Greenland Ice
Sheet using GRACE mascon solutions. D. N. Wiese, N.-J. Schlegel, M. M. Watkins, E. Y. Larour, J. E.
Box, X. Fettweis, M. R. van den Broeke .......................................................................................... 49
Sea Level Extremes ................................................................................................................................ 50
Oral Presentations ............................................................................................................................. 50
Nineteenth Century Sea-level and Extremes on the US East and West Coast. Stefan Talke, David
Jay, Patrick Lau, Conrad Hilley, Lumas Helaire, Drew Mahedy, Ramin Familkhalili ...................... 50
Storm surge clustering and spatial footprints: How extreme was the 2013-2014 UK storm surge
season? Ivan D. Haigh, Matthew P. Wadey, Shari L. Gallop, Robert J. Nicholls ............................ 50
Regional climate variability in extreme sea levels from satellite altimetry observations over two
decades. Melisa Menendez, Philip L. Woodworth ......................................................................... 51
Time varying trends in sea level extremes. Marta Marcos, Francisco M. Calafat, Angel Berihuete,
Sönke Dangendorf .......................................................................................................................... 51
Cyclone Xaver seen by Geodetic Observations. Leonor Mendoza, Luciana Fenoglio-Marc, Remko
Scharroo, Alessandro Annunziato, Matthias Becker, John Lillibridge ............................................ 52
Future storm surge levels - the example of Denmark. Kristine S. Madsen, Torben Schmith, Tian
Tian ................................................................................................................................................ 52
Meteorological Tsunamis In The World Oceans: An Overview. Alexander Rabinovich ................. 53
The impact of sea level rise on storm surge water levels and wind waves. Arne Arns, Jürgen Jensen
....................................................................................................................................................... 53
Atmospheric Circulation Changes and their Impact on Extreme Sea Levels and Coastal Currents in
Australia. Kathleen L. McInnes, Frank Colberg, Julian O’Grady ..................................................... 54
Global Secular Changes in different Tidal High Water, Low Water and Range levels. Robert J.
Mawdsley, Ivan D. Haigh,N.C. Wells ............................................................................................. 54
Posters ............................................................................................................................................... 55
How to interpret expert judgment assessments of 21st century sea-level rise? Hylke de Vries,
Roderik S.W. van de Wal ................................................................................................................ 55
Long-term changes in sea level extremes and tides on the Chinese coasts. Xiangbo Feng, M. N.
Tsimplis and P.L. Woodworth......................................................................................................... 55
Expected Vertical Load in coastal GPS due to a Tsunami like the 1775 Lisbon Tsunami: GPS Tsunami
Early-Warning capabilities. Leonor Mendoza ................................................................................ 55
Analysis of recent high-frequency sea level events in the European Atlantic coast: impact on the
design of automatic algorithms for tsunami detection. Begoña Pérez Gómez, Marta Gómez Lahoz,
Enrique Álvarez Fanjul, Carlos González, François Schindele ......................................................... 56
Estimation extreme sea levels from the combination of tides and storm surges for the coasts of
the Sea of Okhotsk. Georgy Shevchenko ....................................................................................... 56
Global and Regional Sea Level Variability and Change
Palma de Mallorca, June 10-12, 2015
Spatial variation in extreme water levels in the Baltic Sea – North Sea transition from tide gauge
records. Carlo Sørensen, Ole B. Andersen, Per Knudsen ................................................................ 57
The Impact of an Eroding Barrier Island on Extreme Water Levels in the Tampa Bay Area. Marius
Ulm, Arne Arns, Jürgen Jensen ....................................................................................................... 57
Coastal Impacts of Sea Level Changes ................................................................................................... 58
Oral Presentations ............................................................................................................................. 58
Evaluating uncertainties in future coastal flooding occurrence as sea-level rises. Gonéri Le
Cozannet, Jeremy Rohmer, Anny Cazenave, Déborah Idiera, Roderik Van de Wal, Renske de Winter,
Rodrigo Pedreros, Yann Balouin, Charlotte Vinchon, Carlos Oliveros ............................................ 58
Effects of scale and input data on assessing the future impacts of coastal flooding. An application
of DIVA for the Emilia-Romagna coast. Claudia Wolff, Athanasios T. Vafeidis, Daniel Lincke,
Christian Marasmi, Jochen Hinkel .................................................................................................. 58
An assessment of extreme sea levels, waves and coastal flooding in the Maldives. Matthew
Wadey, Ivan Haigh, Sally Brown, Robert Nicholls .......................................................................... 59
Land subsidence and sea level rise at Lipari island (Italy): implications for flooding scenario. Anzidei
Marco, Bosman Alessandro, Carluccio Roberto, Carmisciano Cosmo, Casalbore Daniele, Chiappini
Massimo, Chiocci Francesco Latino, D’Ajello Caracciolo Francesca, Esposito Alessandra, Fabris
Massimo, Muccini Filippo, Nicolosi Iacopo, Pietrantonio Grazia, Sepe Vincenzo, Vecchio Antonio
....................................................................................................................................................... 60
Posters ............................................................................................................................................... 60
Simulating overtopping and coastal flooding in urban areas: Perspectives to quantify sea level rise
effects. Sylvestre Le Roy, Rodrigo Pedreros, Camille André, François Paris, Sophie Lecacheux,
Fabien Marche, Charlotte Vinchon ................................................................................................ 60
Tidal influence on high frequency harbor oscillations in a narrow entrance bay. S. Monserrat, I.
Fine, A. Amores, M. Marcos ........................................................................................................... 61
A probability-based method to estimate sea level rise and future flooding risks on the Finnish
coast. Hilkka Pellikka, Milla M. Johansson, Ulpu Leijala, Katri Leinonen, Kimmo K. Kahma ......... 61
Combining sea state and land subsidence rates in an assessment of flooding hazards at the Danish
North Sea coast. Carlo Sørensen, Niels Broge, Per Knudsen, Ole B. Andersen .............................. 62
Special session on Mediterranean sea level .......................................................................................... 62
Oral Presentations ............................................................................................................................. 62
To what extent can Mediterranean sea level evolve differently from global sea level rise?. Gabriel
Jordà, Damià Gomis, Marta Marcos .............................................................................................. 62
On the connection between the sea level variability in the Mediterranean and in the Black Seas.
Denis Volkov, Felix Landerer .......................................................................................................... 63
Meteotsunamis in the Mediterranean Sea: rare but destructive extreme sea level events occurring
under specific synoptic conditions. Ivica Vilibic, Jadranka Sepic ................................................... 63
Global and Regional Sea Level Variability and Change
Palma de Mallorca, June 10-12, 2015
Τsunami impact in the European-Mediterranean region from the antiquity up to the present.
Gerassimos A. Papadopoulos, Georgia Diakogianni, Anna Fokaefs, Antonia Papageorgiou, Ioanna
Triantafyllou ................................................................................................................................... 64
Evolution of sea level and other variables on the XXI century: a picture derived from Vanimedat II
and ESCENARIOS projects. Enrique Álvarez Fanjul, Damià Gomis, E. Rodríguez-Camino, Marta
Marcos, Gabriel Jordà, R. Aznar, J. C. Sánchez-Perrino, A. Martínez Asensio, J. Llasses, Elena
Padorno, Begoña Pérez, M. N. Tsimplis, F.M. Calafat, Samuel Somot, F. Sevault, F. Adloff, J. M.
Rodríguez ....................................................................................................................................... 64
Future evolution of sea level extremes along the Mediterranean coastline as produced by the
superposition of storminess and sea level rise. Piero Lionello, Dario Conte, Luigi Marzo, Luca
Scarascia ........................................................................................................................................ 65
Posters ............................................................................................................................................... 65
Sea level at 2ka BP in the Balearic Islands from Roman age coastal quarries. Fabrizio Antonioli,
Marcus Heinrich Hermanns, Marco Anzidei................................................................................... 65
Sensitivity of the Mediterranean sea level to atmospheric pressure and free surface elevation
numerical formulation in NEMO. Antonio Bonaduce, Paolo Oddo, Nadia Pinardi, Antonio Guarnieri
....................................................................................................................................................... 66
Rescuing historic Maltese tide gauge data. Elizabeth Bradshaw .................................................. 66
Long-wave analysis of coastal sea-level records and implications for hazard monitoring and
assessment: an application to the Siracusa, Italy, tide-gauge station. Lidia Bressan, Stefano Tinti
....................................................................................................................................................... 67
Mesoscale eddies in the Western Mediterranean Sea. Romain Escudier, Ananda Pascual, Pierre
Brasseur, Lionel Renault................................................................................................................. 67
Improved satellite altimeter mapped sea level anomalies in the Mediterranean Sea. Marta
Marcos, Ananda Pascual, Isabelle Pujol......................................................................................... 68
Determination of Mean Dynamic Topography over the Mediterranean Sea from Jason-2 Altimetry
Measurements and EGM2008 Data. Ali Rami, Sofiane Khelifa ..................................................... 68
Interannual variability of the Surface Geostrophic Circulation of the Mediterranean Sea. M.
Sempere, S. Esselborn, I.Vigo ......................................................................................................... 69
Seasonal Cycle of Surface Geostrophic Circulation of the Mediterranean Sea. M.Sempere, I. Vigo,
M. Trottini, S. Esselborn ................................................................................................................. 69
High-frequency sea-level oscillations in the Mediterranean Sea: analysis and synoptic
preconditioning. Jadranka Sepic, Ivica Vilibic, Amaury Lafon, Loic Macheboeuf, Zvonko Ivanovic
....................................................................................................................................................... 70
Mean sea level secular trends from PSMSL RLR data: A case study for the Mediterranean basin.
Hebib Taibi , Mahdi Haddad .......................................................................................................... 70
Relative sea level trend and long term variability in the Northern Mediterranean from tide gauge
data: implications for future projections. Antonio Vecchio, Marco Anzidei .................................. 70
Global and Regional Sea Level Variability and Change
Palma de Mallorca, June 10-12, 2015
Keynotes speakers
Sea-level changes during past centuries reconstructed from salt-marsh sediments. Prof.
Roland Gehrels, University of York, UK
In recent years a number of sea-level records have been published that use salt-marsh sediments, and
the fossils contained within, as indicators of sea-level change. High-quality sea-level reconstructions
from salt-marsh sediments have now been established for coastal sites in eastern North America (Nova
Scotia, Maine, Connecticut, New Jersey, North Carolina, Florida), Europe (Iceland, Scotland, England,
northern Spain), New Zealand and Tasmania. These proxy records are particularly useful because they
can provide high-resolution sea-level data beyond the period that is covered by tide gauges, including
the centuries immediately preceding the observational era. The overlap with tide-gauge records
provides a check on the validity of the proxy reconstructions. The chronology of proxy records is
provided by a range of radiometric dating techniques (AMS14C, 210Pb, 137Cs, 241Am) and by specific
stratigraphic markers (e.g., pollen, tephra, Pb concentrations, Pb isotopic ratios, paleomagnetism).
High-precision Accelerator Mass Spectrometry (AMS) 14C dating, in combination with bomb-spike
AMS14C analyses, is used to circumvent limitations associated with radiocarbon dating. The resolution
of proxy records depends on the sedimentation rates in the marshes and is usually on the order of one
or two data points per decade.
Many salt-marsh based proxy sea-level records show a marked positive inflexion in the late 1800s or
the early 1900s. Combined with long tide-gauge records they demonstrate that in the first half of the
20th century the rate of sea-level rise started to exceed the late Holocene background value. The
magnitude of the 19th/20th inflexion is large in southern hemisphere sites compared to the North
Atlantic which could point at northern hemisphere land-based ice as an important melt source for a
global sea-level acceleration in the early 20th century. Along the North American east coast there is
some evidence for a period of accelerated sea-level rise in the late 18th century, when rates
approached those that have been observed in the 20th century. In Iceland the highest rates of sealevel rise occurred during positive shifts of the reconstructed North Atlantic Oscillation (NOA) index. A
19th/20th century sea-level acceleration is muted in the eastern Atlantic. Accelerations of sea-level
rise in the North Atlantic are confined to the regional scale and are possibly driven, at least in part, by
re-distribution of water masses due to changes in long-term wind patterns. Without exception all saltmarsh proxy sea-level records show that the highest rates of sea-level rise of the last 2000 years were
achieved during the 20th century.
Considering vertical land motion in understanding sea level change. Prof. Guy
Woppelmann, University of La Rochelle, France
Vertical land motion plays an important role in understanding sea level change over multi-decadal to
century timescales. On the one hand, they need to be corrected in sea level trends recorded by tide
gauges to derive the climatic contributions to sea level. On the other hand, they need to be considered
to understand and anticipate the magnitude of future sea levels along specific coastlines. Indeed,
Global and Regional Sea Level Variability and Change
Palma de Mallorca, June 10-12, 2015
vertical land motion can substantially amplify or attenuate sea level rise from the sole climatic
contributions. In any case, whether global or local, an accurate estimate of vertical land motion
appears mandatory. In this presentation, we will review how vertical land motion has been considered
in past estimates of global sea level change, how it can be determined and what are the current limits
in its accurate observation for understanding relative sea level changes at the coast.
The time-mean ocean dynamic topography: How well can we measure, model, and
understand it?. Prof. Chris W. Hughes, National Oceanography Centre, UK
The combination of altimetry with GOCE and GRACE gravimetry means we now have an accurate global
picture of the mean ocean dynamic topography. Addition of tide gauges, GNSS positioning, and
regional gravity measurements extends this knowledge to points precisely at the coast. With a global
range of about three metres, it is clearly important that we understand how this dynamic component
of sea level is maintained, if we are to have confidence in model predictions of how it might change.
In this talk, I will address the question of how well current ocean models can reproduce the observed
mean dynamic topography, and how well we understand the reasons for those observations. While
the models do a generally good job, I will argue that our understanding remains rather patchy for the
open ocean, and is still quite rudimentary for coastal sea level.
What are the challenges facing quantifying impacts and adapting to global sea-level rise?.
Dr. Sally Brown, University of Southampton, UK
Sea-level rise and extreme events pose on-going and long-term threats to coastlines, particularly
where hazards coincide with human population. Globally, up to 5% of the population could be affected
annually by sea-level rise by 2100 if protection standards are not raised. Such a situation in unlikely as
often humans and natural environments are responsive to change, whether due to a sudden event, or
resulting from slow incremental changes. This represents challenges: Firstly, with much uncertainty in
the projections of sea-level rise and other drivers, what levels will humans or the natural environment
be adapting to? Secondly, given a response to reduce impacts, what will be affected and where will
impacts occur? Thirdly, how will that adaptation take place?
To answer these questions, this presentation explores how past sea-levels, vertical land movements,
present observations, plus extreme events influence future projections of impacts and adaptive
responses. Sea-level rise projections and impacts today will be analysed from global to local scales,
including areas that are particularly at risk world-wide. Adaptation to reduce impacts will also be
considered, from successful past adaptation where transitions to safer coasts have been made, to
potential future responses.
Increasingly the assessment of impacts requires a systems approach, understanding multiple drivers
of coastal changes. Recognition into multiple drivers of change, their interactions and relative
importance is increasingly, such as how population and economic growth can influence or induce
impacts. Gathering accurate data on coastal change and impacts is sometimes challenging today, not
alone for the future. The adaptation challenge remains in enabling long-term climate change
Global and Regional Sea Level Variability and Change
Palma de Mallorca, June 10-12, 2015
adaptation today, without compromising short-term needs, development and livelihoods. Thus, whilst
sea-level rise is an important driver of change, it is increasingly recognised that other drivers can be
more responsible for adverse impacts of change: Sea-level rise remains a societal challenge, depending
on good governance to identify, monitor and reduce impacts.
Semi-empirical modelling of sea-level change. Prof. Stefan Rahmstorf, Postdam
University, Germany
The talk will discuss the semi-empirical approach to modelling sea level, its robustness and validation
issues, and the role that paleo-climatic data can play in constraining the parameters for future sealevel rise.
References:
Rahmstorf, S. (2007), A semi-empirical approach to projecting future sea-level rise, Science, 315(5810),
368-370, doi:10.1126/science.1135456.
Vermeer, M., and S. Rahmstorf (2009), Global sea level linked to global temperature, Proceedings of
the National Academy of Sciences of the United States of America, 106(51), 21527-21532,
doi:10.1073/pnas.0907765106.
Kemp, A. C., B. P. Horton, J. P. Donnelly, M. E. Mann, M. Vermeer, and S. Rahmstorf (2011), Climate
related sea-level variations over the past two millennia, Proceedings of the National Academy of
Sciences of the United States of America, 108(27), 11017-11022, doi:10.1073/pnas.1015619108.
Rahmstorf, S., M. Perrette, and M. Vermeer (2012), Testing the robustness of semi-empirical sea level
projections, Clim. Dyn., 39(3-4), 861-875, doi:10.1007/s00382-011-1226-7.
Schaeffer, M., W. Hare, S. Rahmstorf, and M. Vermeer (2012), Long-term sea-level rise implied by 1.5
degrees C and 2 degrees C warming levels, Nature Clim. Change, 2(12), 867-870,
doi:10.1038/nclimate1584.
Bittermann, K., S. Rahmstorf, M. Perrette, and M. Vermeer (2013), Predictability of twentieth century
sea-level rise from past data, Environmental Research Letters, 8(1), doi:10.1088/17489326/8/1/014013.
Tide gauge reconstructions and the separation of regional and global mean sea level
signals. Prof. Mark Merrifield, University of Hawaii, USA
Reconstructions of global mean sea level (MSL) based on tide gauge datasets include decadal time
scale fluctuations that have drawn considerable attention. These low frequency MSL fluctuations have
been attributed to various physical phenomena, including volcanic activity, enhanced land ice melt,
and changes in ocean circulation and heat uptake. Alternatively, the limited spatial sampling afforded
by the tide gauge network may lead to the misrepresentation of regional sea level variability into the
global mean. To gain further perspective on this issue, we review various ways that changing surface
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winds result in regional sea level patterns, and consider how effective the tide gauge array is at
distinguishing these patterns from MSL change. We use the tide gauge data to highlight that regional
variations detected during the satellite altimeter period are not necessarily stationary over the past
century, and that the sparse array prior to the mid 1950s is poorly suited for the separation of regional
and global patterns. Lastly, we consider prominent MSL decadal variations in various tide gauge
reconstructions and examine the potential for contamination of regional sea level signals into the
mean.
Sea level variability: from surface gravity waves to mean sea level. Prof. Charitha
Pattiaratchi, University of Western Australia, Australia
Coastal sea level variability occurs over a range timescales ranging from seconds to centuries.
The action of the wind on the sea surface generates surface gravity waves with periods of the order of
10s and plays a major role in defining coastal processes. Infra-gravity waves with periods 30-300 s
influence oscillations in semi-enclosed basins such as ports and harbours. Globally, the astronomical
forces of the Sun and the Moon result in tidal variability with periods of 12 and 24 hours as well as tidal
modulations with periods up to 18.6 years. In many regions, the effects of the tides dominate the
water level variability – however, in regions where the tidal effects are small other processes also
become important in determining the local water level. In this presentation, sea level data from
Fremantle (tidal range ~0.5m), which has one of the longest time series records in the southern
hemisphere, and other sea level recoding stations from Western Australia are presented to highlight
the different processes ranging from seiches, tsunamis (generated through earthquake and
meteorological events), tides, storm surges, continental shelf waves and annual and inter-annual
variability. As the contribution from each of these processes is of the same order of magnitude – the
study of sea level variability in the region is very interesting and reveals both local and remote forcing.
Modelling historical and future mean sea level change. Prof. Jonathan Gregory, University
of Reading, UK
The rate of global mean sea level rise (GMSLR) has accelerated during the last two centuries, from the
order of magnitude of 0.1 mm yr-1 during the late Holocene, to about 1.5 mm yr-1 for 1901-1990, with
ocean thermal expansion and glacier mass loss being probably the dominant contributors. Processbased models suggest that the larger rate of rise since 1990, of about 3 mm yr-1, results from increased
radiative forcing of global climate change, and from increased ice-sheet outflow induced by warming
of the immediately adjacent oceans. Ocean thermal expansion is the largest contributor to projections
of GMSLR during the 21st century. For a given scenario, there is a substantial spread in climate model
projections of global ocean heat uptake and thermal expansion, and in the geographical pattern of sea
level change due to ocean density and circulation change. Larger uncertainty in projections of GMSLR
comes from the land-ice contributions, especially ice-sheet dynamical change. These contributions also
influence regional sea-level change, through their effect on gravity and the solid Earth. By 2100 the
rate of GMSLR for a scenario of high emissions could approach the average rates that occurred during
the last deglaciation, whereas for a strong emissions mitigation scenario it could stabilise at rates
Global and Regional Sea Level Variability and Change
Palma de Mallorca, June 10-12, 2015
similar to those of the early 21st century. In either case, GMSLR will continue for many subsequent
centuries, because of the long timescales of ice-sheet change and deep-ocean warming, and could be
partly irreversible.
Status and challenges on sea level monitoring and forecasting in the Mediterranean Dr.
Begoña Pérez Gómez, Puertos del Estado, Spain
After a review of the main characteristics of the relevant sea level processes and variability expected
in the Mediterranean sea, a detailed analysis of the adequacy of the existing monitoring networks and
forecasting systems in the region is presented. The tide gauges spatial distribution and their data
sampling and latency will be first considered, in order to determine the capability of the existing insitu network to fulfill the new requirements not only of climate scientists and oceanographers but also
of the sea level related hazards warning systems. The latter include both storm surge and tsunami
warning. For years storm surge forecasts have not been a priority in the Mediterranean; however, a
new set of forecasting systems are in operation nowadays, what reveals the interest of this variable,
reinforced by the expected increase of mean sea level for the next decades. Operational general
circulation models are now being designed for including sea level forecasts for this reason. On the
other hand, the risk of tsunamis in the Mediterranean is significantly larger than in the rest of Europe:
having access to high-frequency sea level data in real time from the entire basin is crucial for an early
detection and final early warning to the population: in this aspect the lack of stations from the North
of Africa is a great weakness of the regional tsunami warning systems.
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Paleo Sea Level
Oral Presentations
Holocene relative sea level changes in the Baltic Sea basin: syntheses of geological and
archaeological data. Alar Rosentau
In the early phases of cultural development, Mesolithic and Neolithic human populations in the Baltic
region experienced periods of significant marine transgressions and regressions owing to the melting
of the continental ice sheet and glacial isostatic land uplift. Geological–archaeological studies in the
southern Baltic Sea area have revealed a number of Mesolithic and Neolithic traces of human
occupation off the Danish and German coasts as a result of Holocene sea-level rise. Prehistoric coastal
sites in the northern Baltic Sea areas have, however, been uplifted and are located successively at
different altitudes as a result of glacial rebound. In transitional areas, prehistoric man experienced
transgressions and regressions of the shifting coastline owing to competition between glacial rebound
and eustatic sea level rise. In the current paper case studies form the transitional area will be presented
demonstrating the potential of archaeological records for reconstruction of transgressions and
regressions during the Litorina Sea. Geological and archaeological data indicate acceleration in sealevel rise rates around 7.8 and 7.6 cal. ka BP when relative sea-level rose c. 6 m within c. 500 years.
This caused the flooding of peat and palaeosoil layers, by the submergence of the Mesolithic sites and
by the abrupt appearance of brackish water diatoms in different small lake basins. The SPLASHCOS
COST Action TD0902 completed in 2013 is producing an Atlas of over 2500 submerged prehistoric sites
that may be useful in palaeo-sea level reconstructions.
Sea-level changes in the western Mediterranean during the last 12,000 years: a tool to better
constrain the future projection of sea-level rise. Matteo Vacchi, Nick Marriner, Christophe
Morhange, Giorgio Spada, Alessandro Fontana, Alessio Rovere
Global sea-level rise is the result of an increase in the ocean volume, which evolves from changes in
ocean mass due to melting of continental glaciers and ice sheets, and the expansion of ocean water as
it warms. The elevation of the ocean surface relative to the ocean floor is defined as a relative sea level
(RSL), and any shift in height of either of these two surfaces produces a RSL change. Present-day sea
level variations in the Mediterranean depend on various factors, including recent climatic forcing,
tectonic activity, anthropogenic effects, and glacio-isostatic adjustment. Our understanding of current
rates of sea-level rise from tide gauge and satellite data, requires correction for glacial isostatic
adjustment (GIA) effects that are both calibrated to, and independently tested by, observations of
former sea levels. With this purpose, we created a database of Holocene (last 12.0 ka) geological and
geo-archeological sea-level data across the Western Mediterranean. We reconsidered ~600 published
and unpublished sea-level data along the western Mediterranean Sea and we proposed a standardized
approach for the production of index and limiting points following the protocol described by the
International Geoscience Programme (IGCP) projects 61, 200, 495 and 588. We then reconstructed the
RSL histories in 21 regions located in Spain, France, Italy, Malta, Tunisia, Slovenia and Croatia. At the
basin scale, RSL rose rapidly from 12.0 to 6.0 ka BP. Younger data showed a significant decrease in the
rising rates in the last 7.5 ka. During the late Holocene (last 4.0 ka BP) GIA, sediment compaction and
Global and Regional Sea Level Variability and Change
Palma de Mallorca, June 10-12, 2015
local neotectonic activity played a major role in controlling sea-level variability between regions.
Preliminary comparison with long-term tidal gauge data (>50 years) indicates a significative increase
in rates of sea-level rise during the last 100 years.
Results of this study are relevant for understanding how GIA operates in the far field of late-Pleistocene
ice sheets and to assess sea level rise hazards, which are particularly magnified in low-lying or subsiding
coastal areas.
Late Holocene sea-level change in the Falkland Islands: testing the Greenland melt hypothesis.
Newton, T. L., Gehrels, W. R., Daley, T.J., Blake, W.
Instrumental and proxy sea-level records indicate that 20th century sea-level rise (SLR) in the North
Atlantic Ocean departed significantly from average late Holocene trends reconstructed by geological
methods. Southern hemisphere instrumental records are too short to identify any recent acceleration.
Recent studies have documented the inflexion in proxy records from New Zealand and Tasmania,
giving rise to the hypothesis that the 20th century sea-level acceleration was global in extent.
Importantly, the magnitude of change in the rate SLR at the beginning of the 20th century is greater in
southern hemisphere sites than in the North Atlantic. Such spatial differences are potentially highly
significant as sea-level theory predicts that land-based ice melt produces increased rates of SLR in the
far-field locations from which the melt source is located. The greatest rates of SLR as a consequence
of Greenland melt are predicted to be in the South Atlantic Ocean, in the seas surrounding the Falkland
Islands.
To test this hypothesis we present a new late Holocene relative sea-level (RSL) record for the Falkland
Islands, the first for this region. Our reconstruction is based on palaeo-sea level positions derived from
diatom, testate amoebae and foraminifera analyses obtained from saltmarsh sediments. The
reconstruction shows that RSL in the Falkland Islands for much of the last 7000 years was within 0.7m
of present RSL. Our high-resolution reconstruction for the last ~2000 years documents a rising trend
in RSL with a recent inflexion toward present sea level for the most recent part of the record. This
pattern of sea-level change is consistent with proxy records from Tasmania and New Zealand which
suggest that northern hemisphere land-based ice was the most significant melt source for late
Holocene global sea-level rise.
Posters
Decoding sea level changes during the MIS 5 by means of Phreatic Overgrowths on Speleothems
(POS) research in coastal caves of Mallorca (western Mediterranean). Joan J. Fornós, Àngel Ginés,
Joaquín Ginés, Francesc Gràcia, Yemane Asmeron, Bogdan P. Onac, Victor Polyak, Paola Tuccimei
The littoral caves of southeastern Mallorca have formed by the mixing of freshwater and seawater in
the coastal phreatic zone, and are extensively decorated with speleothems that formed during
Quaternary times when the caves become air-filled chambers. Throughout the Middle and Upper
Pleistocene the caves were repeatedly flooded by glacio-eustatic sea level oscillations. The water level
of each flooding event was recorded by a distinct encrustation (a Phreatic Overgrowth on
Speleothems, POS) of calcite or aragonite deposited less than 40 cm below the brackish water/air
Global and Regional Sea Level Variability and Change
Palma de Mallorca, June 10-12, 2015
interface (water table) at elevations equivalent to sea-level, over existing speleothems and along cave
walls.
These carbonate precipitates, which appear as horizontal alignments of crystallizations delimiting the
tidal fluctuation range of the coastal water-table, are excellent recorders of sea level changes, being
readily datable by U-series methods.
Thus, stable sea-level stands result in POS that have grown large enough to be used as accurate sealevel markers. Marine isotope stage (MIS) 5 of the last interglacial (LIG) is of great interest because it
serves as an analog for the Holocene. Changes in sea-level are, in part, indicative of the global-scale
changes in climate.
Acknowledgements: This research has been supported by the MINECO projects CGL 2010-18616 and
CGL-2013-48441-P to JJF and by a NSF grant AGS 1103108 to BPO and VJP
Sea-level highstands in Mallorca during the last interglacial. Thomas Lorscheid, Paolo Stocchi,
Alessio Rovere, Lluís Gómez-Pujol, Bas de Boer, Thomas Mann, Hildegard Westphal, Joan J. Fornós
Deposits of the last interglacial, analysed in light of glacio-hydro-isostatic adjustment models, can
provide us with information on the sea-level history and the response of polar ice-sheets in slightly
warmer climates. Mallorca is one of the key areas in the Western Mediterranean for such deposits.
The outcrops representing this period were intensely investigated by several authors since CUERDA
1979. According to their observations, the sedimentological and fossil content is well known and the
age was determined by the presence of the Senegalese fauna and, more recently, by dating with U/Th
and AAR. Three aspects of Mallorcan deposits were still underinvestigated. i) precise elevation
measurements with differential GPS. ii) estimates of reference water level and indicative range of the
deposits and landforms at each site. iii) estimates of glacial isostatic adjustment (GIA) effects since MIS
5e.
In this study we present the results of two field trips aimed at measuring last interglacial deposits in
Mallorca with high-accuracy GPS and establishing, using modern shorelines as analogs, indicative
ranges and reference water level values for paleo deposits. We then used an earth-ice coupled GIAmodel to investigate isostatic adjustment since MIS 5e in the island, and compared the elevation of
our deposits to the expected GIA signal in this region. We discuss our results in terms of tectonics and
eustasy.
Vertical Land Movements
Oral Presentations
Combination Results of the Tide Gauge Benchmark Monitoring (TIGA) Analysis Centre Reprocessing Products. Addisu Hunegnaw, Norman Teferle
In 2013 the International GNSS Service (IGS) Tide Gauge Benchmark Monitoring (TIGA) Working Group
(WG) started their re-processing campaign, which proposes to re-analyze all relevant Global
Positioning System (GPS) observations from 1994 to 2013. This re-processed data set will provide highquality estimates of vertical land movements for more than 400 stations, enabling regional and global
high-precision geophysical/geodetic studies. Several of the TIGA Analysis Centres (TACs) have
completed processing the full history of GPS observations recorded by the IGS global network and
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Palma de Mallorca, June 10-12, 2015
many other GPS stations at or close to tide gauges, which are available from the TIGA data centre at
the University of La Rochelle (www.sonel.org). Following the recent improvements in processing
models and strategies, this is the first complete re-processing attempt by the TIGA WG to provide
homogeneous position time series.
In this study we report on a first multi-year weekly combined solution from the TIGA Combination
Centre (TCC) at the University of Luxembourg (UL). Using two independent combination software
packages, CATREF and GLOBK, we have computed a first solution of the TAC solutions already available.
These combinations allow an evaluation of any effects from the combination software and of the
individual TAC parameters and their influences on the combined solution. Some major results of the
UL TIGA multi-year combinations in terms of geocentric sea level changes will be presented and
discussed.
Models of land uplift in northern Europe. Holger Steffen
Glacial isostatic adjustment (GIA) is the dominating process in northern Europe leading to a maximum
absolute land uplift of about 1 cm/year near the Swedish city of Umeå. In contrast, the areas of the
southern Baltic and North seas are subsiding due to the collapse of the peripheral bulge. Both effects
have enormous impact on coastal changes and thus on society and economy, especially in view of
current sea-level rise which may increase or decrease uplift or subsidence depending on the location.
The Nordic countries have developed and are frequently updating land uplift models for usage in the
national geodetic surveys. We present current models that are used as well as further efforts for the
development of high precision and high resolution land uplift and GIA models which could also help in
sea level research. This includes most recent results of land uplift/subsidence and sea-level change for
the North and Baltic seas.
Relative sea level history during the Holocene and models of the glacial isostatic adjustment
process: constraints from the regions of forebulge collapse. Keven Roy, W.R. Peltier
Models of the glacial isostatic adjustment (GIA) process enable us to study and understand the regular
cycles of glaciation and deglaciation that have characterized the Earth's climate over the past 800,000
years or so, in particular in terms of the large variations in sea level that have accompanied them.
These models, which require as fundamental inputs a history of ice-sheet loading and a representation
of the radial variation of mantle viscosity, can be tested and refined by comparing their predictions to
a wide range of geophysical and geological observables, among which inferences of past relative sea
level based upon appropriate geological indicators are particularly important. These geophysical
observables, depending on the region from which they originate, provide constraints on different
features of the GIA process. However, while the relaxation process in regions near former centers of
glaciation can be parametrized in a simple fashion, its evolution in regions of forebulge collapse,
located at the periphery of the former ice sheets, is much more complex.
In this paper, we examine how recently available high-quality geological data sets of relative sea level
history for regions of forebulge collapse, such as that of Engelhart et al. (2011, Geology) for the U.S.
East coast or Engelhart et al. (2015, QSR) for the U.S. West coast, enable us to gain critical information
concerning the response of these regions and provide new complementary constraints on GIA models
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Palma de Mallorca, June 10-12, 2015
and, consequently, on our understanding of relative sea level evolution around the world. In particular,
we will focus on how misfits between these new sea level evolution inferences and current state-ofthe-art GIA model predictions (ICE-6G_C (VM5a) (Peltier et al., 2015, JGR)) can be eliminated, and then
explore the consequences of these changes on our knowledge of the deglaciation history over North
America.
Posters
Updated GPS vertical velocity field at tide gauges: application to global and regional sea level
change. Médéric Gravelle, Alvaro Santamaria-Gomez, Marta Marcos, Phil Thompson, Guy
Wöppelmann
The relative importance of the non-climate contribution of vertical land movement to the observed
rates of sea level change at the coast is investigated based on the last GPS solution of the ULR
consortium taking part to the International GNSS Service (IGS) Repro2 campaign. This solution stems
from 20 years of GPS data (1995-2014) reanalyzed using state-of-the-art models and corrections. It
includes 749 GPS stations distributed worldwide of which 575 are dedicated to a sea level application.
In this study, we correct the tide gauge trends for vertical land movements using the GPS velocity field,
and we investigate global and regional mean sea level estimates
Using InSAR to monitor vertical ground motions in coastal cities. G. Le Cozannet, D. Raucoules, G.
Wöppelmann
Before the altimetry era, tide gauge are a unique source of information to evaluate past sea-level
changes. However, they can be affected by vertical ground motions acting at different space scales.
We use synthetic aperture radar techniques to assess these ground motions and their consequences
for geodetic instruments such as Tide Gauge, GPS, Doris stations. Summarizing results obtained at
Alexandria (Egypt; Woppelmann et al., 2013), Manila (Philippines; Raucoules et al., 2013) and Dakar
(Senegal; Le Cozannet et al., subm.), we identify different situations in terms of data availability and
ground motion context:
when strong ground motions affect the tide gauge, the technique can easily help rejecting tide
gauges records from the database of reliable datasets (case of Manila)
however, when no ground motions can be observed using InSAR in the vicinity of geodetic
instruments (Case of Alexandria and Dakar), it remains challenging to reach the accuracy required to
confirm that tide gauge records are indeed suitable for monitoring sea level changes.
To reach the required accuracy of this InSAR application, a large set of SAR data must have been
acquired over the area. For future science application of Sentinel 1 in the field of geodesy underpinning
sea level science, it will be necessary to define appropriate background missions covering coastal sites
where key records have been aquired.
Global and Regional Sea Level Variability and Change
Palma de Mallorca, June 10-12, 2015
Vertical land movements from the combined use of satellite altimetry and tide gauges. Marta
Marcos, Guy Wöppelmann
Vertical ground displacements at tide gauge sites were estimated from the differenced time series of
monthly satellite altimetry sea level anomalies minus tide gauge. We have used the time series of
satellite altimetry that are routinely processed and distributed by four major data providers (three
gridded and one along-track products) together with monthly tide gauge records from the datum
controlled data set of the Permanent Service for Mean Sea Level (PSMSL). Differenced time series were
built using three variants of altimetric time series. Each resulting record was analyzed assuming a
combination of white noise and power-law noise of a priori unknown spectral index. The rate
uncertainties, computed taking into account the noise content in the differenced time series, will be
discussed. In particular, in the context of the departures from the white noise (expected only if both
the satellite altimeter and the tide gauge were recording mostly the same sea level signals and their
instrumental errors were negligible) and its amplitude. The most suitable altimetric product in terms
of correlation and variance reduction at tide gauges, among those investigated, will be identified. Rates
of vertical land motion computed with Global Positioning System (GPS) and rates obtained from the
combination of altimetry and tide gauge records will be finally compared for those stations where both
measurements are available.
GNSS reflectometry for tide gauge levelling. Alvaro Santamaría-Gómez, Christopher Watson,
Médéric Gravelle, Matt King, Guy Wöppelmann
The GNSS reflectometry (GNSS-R) technique provides valuable information related to the geometry
and physical properties of reflecting surfaces surrounding the GNSS antenna (e.g., Global Positioning
System, GPS), including the vertical distance to them.
Here, we use sea-surface reflections of GNSS signals, recorded as oscillations in the observed signalto-noise ratio (SNR), to estimate the GNSS to tide gauge (TG) levelling connection and thus the
ellipsoidal height of the TG. This can be done remotely, continuously and at no additional cost.
The same technique can be used to monitor sea-surface height changes, transforming the GNSS station
in an alternative TG and thus providing sea-level change in a global height system.
We describe how this technique works, its benefits and limitations, including ongoing work and future
improvements. At the time of writing, comparison with traditional in situ levelling reveals promising
differences at the centimetre level. These differences include errors from this technique, but also
errors related to the traditional in situ levelling (errors in the GNSS antenna calibration) and to the
calibration of the TG zero. The latter opens the possibility of using this technique to monitor the
stability of the TG zero
Leveling for the altimetric control of tide gauge sensors and GNSS permanent stations in
Barcelona’s and Ibiza’s ports. Tapia Gómez, A; López Bravo, R; Gili Ripoll JA; Martínez Benjamín,
JJ; Pros LLavador, F; Palau Teixidò, V
The main objective of the work performed is to determine altimetrics movements that may affect the
data stability, of both tide gauges and global positioning, transmitted by these two types of sensors.
Global and Regional Sea Level Variability and Change
Palma de Mallorca, June 10-12, 2015
We will present the work effected at the port of Barcelona that started in 2011, the year in which
settlements are detected in the area compared to 2008 data, and which have continued until today.
The area where the tide gauge of Puertos del Estado and the GNSS permanent station of the Autoritat
Portuària de Barcelona, distant about 50 meters, are located, is newly reclaimed land sea. Plus, the
GNSS station is located on the roof of the control tower of the port, a building 45 meters high with a
unique metal frame.
As well, we will present the work effected at the port of Ibiza, tide gauge of Puertos del Estado and
GNSS control station on the roof of a building about 10 meters high and distant about 80 meters.
The need for GNSS stations to have a clear horizon, forces their location to be on buildings which
difficult a precise leveling, we will describe leveling geometric designed as ad hoc.
The tasks carried out in the port of Barcelona until September 2014, settlements have been detected
up to 39 millimeters, while in the port of Ibiza the settlements are estimated at a value close to 1
mm/year.
The results confirm that altimetrics checks need to be done periodically starting from the moment they
are installed and in fixed points. The frequency of checks will be determined by the results that are
obtained.
A New Datum-Controlled Tide Gauge Record for Sea Level Studies in the South Atlantic Ocean:
King Edward Point, South Georgia Island. Norman Teferle, Addisu Hunegnaw, Philip Woodworth,
Peter Foden, Simon Williams, Jeffrey Pugh, Angela Hibbert
In 2008 a new pressure tide gauge with Global Sea Level Observing System Number 187 was installed
at King Edward Point (KEP), South Georgia Island, South Atlantic Ocean. This installation was carried
out as part of the Antarctic Circumpolar Current Levels by Altimetry and Island Measurements
(ACCLAIM) programme. In 2013 the KEP Geodetic Observatory was established in support of various
scientific applications including the monitoring of vertical land movements at KEP. Currently, the
observatory consists of two state-of-the-art Global Navigation Satellite System (GNSS) stations with
local benchmark networks. In 2014 a tide board was added to the tide gauge, which, together with the
measurements from the KEP Geodetic Observatory, now enables a calibration of the tide gauge. This
will make it possible to include the KEP tide gauge in the Permanent Service for Mean Sea Level (PSMSL)
database and make it available for future sea level studies.
In this study, we will present the GNSS and levelling observations from the KEP Geodetic Observatory
for the period from February 2013 to May 2015 used for the calibration of the tide gauge. While it is
still too early to obtain accurate vertical land movement estimates from the GNSS data, the levelling
campaigns in 2013 and 2014 indicated 7-9 mm of subsidence near the tide gauge. For the computation
of the new height datum, geoid undulations derived from a seamless combination of the latest Gravity
Observation Combination (GOCO) and Earth Gravitational Model (EGM) 2008 models were used. The
use of this combined gravity model introduced a datum shift of approximately -24 cm compared to the
previous datum.
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Mean Sea Level Observations and Processes
Oral Presentations
The GOCE geoid in support to sea level analysis. Thomas Gruber
The accuracy of the final geoid models derived from GOCE and complementary satellite data is
estimated to be about 1.5 cm with 100 km spatial resolution and worldwide consistency. This opens
new possibilities for sea level research, where geoid quality and consistency over large distances often
plays an important role. One example for this is the problem of connecting tide gauge records across
the oceans. In principle there are two ways to perform this connection. First, via the oceans by
estimating the dynamic ocean topography at the tide gauges from the GOCE geoid and satelllite
altimetry and, second, by unifying the regional or continental height systems to which the tide gauges
are connected by estimating their offsets to the global GOCE geoid. Both approaches in principle
require the true geoid at the tide gauge locations, which not always is provided by the GOCE geoid
because of its limited spatial resolution or in other words due to the omission error, i.e. the part of the
signal which cannot be observed with GOCE. The paper provides a summary of the characteristics of
the GOCE geoid solutions, some results for connecting tide gauges applying both methods and
specifically investigates the impact of the omission error on the results obtained.
On the decadal trend of global mean sea level and its implication on ocean heat content change.
Lee-Lueng Fu
The variability of the trend of global mean sea level on decadal scales is of great importance to
determining its long-term evolution. In this paper we have reexamined the approach to estimating
such a trend. Most climate time series such as the altimeter sea level record are characterized by a
red noise process. The temporal correlation of the residuals from a linear trend fit has often been
neglected in estimating the uncertainly of the fit, leading to underestimate of its errors. We suggest
to cast the problem as optimal estimation to minimize the residuals weighted by autocovariance. The
approach takes into account the various time scales present in the time series and their effects on
estimating a trend. In the case of the altimeter record, the resulting error estimate is a factor of four
larger than estimates neglecting the temporal correlation. Although the dominant error in the
altimetric sea level trend is derived from comparison to tide gauge observations, which have long-term
(tectonic scales) errors from land motions. Such errors essentially cause a bias in the estimate of a
trend over decadal scales. Such bias would be canceled for evaluating the change of decadal trends, of
which the errors are thus dominated by the uncertainty in the estimation error. The approach was
also applied to the sea level change from ocean mass estimated from the GRACE observations of the
change of Earth’s gravity. The steric sea level was then estimated from the difference between the
sea level from altimetry and its mass component from GRACE. The decadal trend of steric sea level
was favorably compared to the Argo observations. The results have shed light on the prospects of
estimating decadal change in ocean heat content from space, a variable of great importance to climate
change and sea level rise.
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Deep-ocean contribution to sea level and energy budget not detectable over the past decade.
W. Llovel, J. K.Willis, F.W. Landerer, I. Fukumori
As the dominant reservoir of heat uptake in the climate system, the world’s oceans provide a critical
measure of global climate change. Here, we infer deep-ocean warming in the context of global sealevel rise and Earth’s energy budget between January 2005 and December 2013. Direct measurements
of ocean warming above 2,000m depth explain about 32% of the observed annual rate of global mean
sea-level rise. Over the entire water column, independent estimates of ocean warming yield a
contribution of 0.77 +/- 0.28mm/yr in sea-level rise and agree with the upper-ocean estimate to within
the estimated uncertainties. Accounting for additional possible systematic uncertainties, the deep
ocean (below 2,000 m) contributes -0.13+/-0.72mm/yr to global sea-level rise and -0.08+/-0.43W/m^2
to Earth’s energy balance. The net warming of the ocean implies an energy imbalance for the Earth of
0.64 +/- 0.44W/m^2 from 2005 to 2013.
Synchronization of sea level to oceanic and atmospheric forcing. Francisco M. Calafat
Synchronization is a basic phenomenon in physics wherein the phases of two oscillators, either chaotic
or periodic, become entrained to a common behaviour through coupling or forcing. Strictly speaking,
the ocean-atmosphere system represents an example of bidirectional coupling in which the two
subsystems mutually influence each other's dynamics, although in many ocean applications one can
assume, without incurring significant error, that the atmosphere is a freely-evolving force acting upon
the ocean. Irrespective of the coupling configuration, the interaction between the two subsystems
can lead to the appearance of relations between some of their properties that are crucial too
understand the evolution of the ocean, especially in a situation of climate change. Here we are
concerned with the synchronization, in the sense of phase-locking, between some of the components
of sea level and their driving forces. In particular, we investigate changes in the dynamics of the phase
of sea level extremes and the seasonal sea level cycle in tide gauge observations in relation to the
evolution of their driving mechanisms such as wind forcing, surface heat fluxes, and hurricane
seasonality. In order to detect phase shifts or locking we explore instantaneous phases via a non-linear
and non-Gaussian state-space model which is learned through a particle Markov chain Monte Carlo
filter.
Annual sea level variability of the coastal ocean: the Baltic Sea-North Sea transition zone.
Marcello Passaro, Paolo Cipollini, Jerome Benveniste
Up to now, the use of satellite altimetry for sea level studies in the coastal regions has been has been
limited due to the lack of confidence in the accuracy of the satellite measurements close to land and
in shallow areas. This research focuses on validating the coastal capabilities of satellite altimetry to
detect the annual cycle of sea level on a regional and sub-regional scale. The study area is the
intersection of North Sea and Baltic Sea.
Coastal-dedicated satellite altimetry data (from ALES) are compared with the state-of-the-art standard
altimetry products (from the ESA Climate Change Initiative). Estimations of the annual cycle of sea level
are also derived from a network of coastal tide gauges. The analysis spans the Envisat years (2002-
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2010) and is performed both along each satellite track (or grid point for the mapped dataset) and by
dividing the area into sub-basins.
We demonstrate that dedicated processing improves the quality of the altimetry dataset in the area,
showing for example that the root mean square difference between the annual cycle sinusoid
estimated by the tide gauges and coastal altimetry within only 15 km of the coast is constantly less
than 1.5 cm. We provide interpretation of the results by using wind stress data and a local climatology,
highlighting small-scale differences, such as a smaller annual variability in the West Arkona due to
steric cycle phase opposed to mass component phase and a slope in the amplitude of the annual cycle
along the Norwegian coast due to a coastal current.
To our knowledge, this is the first time that the improvements brought by coastal satellite altimetry to
the description of the annual variability of the sea level have been evaluated and discussed. The
methodology applied in this paper is generally applicable to other coastal areas and the coastal
reprocessed ALES dataset will soon be available to the community over the whole coastal ocean.
A probabilistic reassessment of 20th century global mean sea level. Carling Hay, Eric Morrow,
Robert E. Kopp, Jerry X. Mitrovica
Tide gauge observations of sea level over the 20th century show significant spatial and temporal
variability on a continuum of length and time scales. The variability seen in these records is due to
processes that include ongoing sea-level changes due to glacial isostatic adjustment (GIA), thermal
expansion of the ocean, dynamic effects associated with ocean circulation changes and oceanatmosphere interactions, and present day melting of land ice. The geographic signatures associated
with this latter process are unique for every ice sheet and glacier, and can be used, in principle, to
estimate the contribution of each source to global sea-level change. The combination of data sparsity
and geographic variability makes it challenging to obtain robust estimates of global mean sea level
(GMSL).
We overcome the difficulties associated with the tide gauge records by modeling the underlying
physics responsible for the observed geographic variability in the observations. This allows us to infer
global information from the incomplete records. Using two probabilistic techniques, we conclude that
GMSL rose at 1.2 ± 0.2 mm/yr over the time period 1901-1990, ~30-40% lower than previous estimates.
This lower rate agrees with the sum of the estimated individual GMSL contributions recently reported
in the Fifth Assessment Report of the IPCC, allowing us to close the 20th century sea-level budget. By
contrast, our estimated rate for the period 1993-2010 (3.0 ± 0.7 mm/yr) agrees with previously
published results, suggesting that the acceleration of sea-level rise over recent decades has been
significantly greater than previously thought.
Considerations for Estimating the 20th Century Trend in Global Mean Sea Level. Philip R.
Thompson, Benjamin D. Hamlington
Recent reconstruction efforts result in a range of published estimates for the 20th century trend in
global mean sea level (GMSL). Discrepancies can be attributed to two factors: 1) differences in analysis
and/or reconstruction techniques; and 2) differences in tide gauge selection and quality control of the
data. In this paper, we isolate the effect of tide gauge selection on estimates of GMSL by applying a
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simple and consistent analysis technique to the sets of tide gauges used in three recent publications:
Ray and Douglas (2011), Church and White (2011), and Hay et al. (2015). We describe the differences
in selection philosophy employed by each study, and we show how tide gauge selection choices can
affect estimates of the long-term global trend derived from each set. In particular, we find that
discrepancies between 20th century GMSL trend estimates are related to the decision to include or
exclude gauges from a small number of coastal regions. These regions exhibit large-scale coherent
variability and/or long-term trends that are inconsistent with changes in GMSL, and we conclude that
any reconstruction including gauges from these regions must demonstrate the ability to account for
this non-global variability using non-uniform basis functions. Finally, we demonstrate how to treat tide
gauge selection as an analytical process and examine the tide gauge residuals from GIA and fitted nonuniform basis functions in a reconstruction. We show which tide gauge records contain reasonable
long-term trends and regional variability consistent with spatial basis functions derived from altimetry.
We also evaluate which altimetry basis functions are actually useful when accounting for decadal and
longer sea level variability in tide gauges. The balance between including more tide gauge data vs. the
limitations of the basis functions available to the reconstruction is key to achieving optimal estimates
of 20th century GMSL trends.
Detecting sea level seasonality in the northwestern Pacific. Xiangbo Feng, M. N. Tsimplis, M.
Marcos and F. M. Calafat
Tide gauges and AVISO altimetry data are used to investigate the seasonal sea level cycles in the whole
region of the NW Pacific, along with other atmospheric and oceanographic reanalysis. The regression
model of seasonal cycles can explain over 60% of sea level variations in vast majority of the region,
with higher values in the northern marginal seas. The annual cycle parameters based on three different
data sources, i.e. tide gauges, AVISO and Simple Ocean Data Assimilation (SODA), were intercompared. We found that in relation to tide gauge observations AVISO usually underestimates the
annual cycle amplitude at half of stations by overall 3.5cm. Compared with observations, SODA can
well capture the seasonal cycles in vast majority of area, except in the shallow water regions, but
overestimate the magnitude of inter-annual variability. The forcing of seasonal sea level signals was
explored, such as the attributions from atmosphere pressure, steric height, wind regimes and ocean
surface current.
Detection and attribution of global mean thermosteric sea level change. Aimée B. A. Slangen,
John A. Church, Xuebin Zhang, Didier Monselesan
Changes in sea level are driven by a range of natural and anthropogenic forcings. To better understand
the response of global mean thermosteric sea level change to these forcings, we compare three
observational data sets to experiments of 28 climate models with up to five different forcing scenarios
for 1957–2005. We use the preindustrial control runs to determine the internal climate variability. Our
analysis shows that anthropogenic greenhouse gas and aerosol forcing are required to explain the
magnitude of the observed changes, while natural forcing drives most of the externally forced
variability. The experiments that include anthropogenic and natural forcings capture the observed
increased trend toward the end of the twentieth century best. The observed changes can be explained
by scaling the natural-only experiment by 0.70 +/- 0.30 and the anthropogenic-only experiment
(including opposing forcing from greenhouse gases and aerosols) by 1.08 +/- 0.13 (+/-2𝜎).
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Detecting anthropogenic footprints in sea level rise. Sönke Dangendorf, Marta Marcos, Alfred
Müller, Eduardo Zorita, Jürgen Jensen
While there is scientific consensus that global mean sea level (MSL) is rising since the late 19th century,
it remains unclear how much of this rise is due to natural variability or anthropogenic forcing.
Uncovering the anthropogenic contribution requires profound knowledge about the persistence of
natural MSL variations. This is challenging, since observational time series represent the superposition
of various processes with different spectral properties. Here we statistically estimate the upper bounds
of naturally forced centennial MSL trends on the basis of two separate components: a slowly varying
volumetric (mass and density changes) and a more rapidly changing atmospheric component. Resting
on a combination of spectral analyses of tide gauge records, ocean reanalysis data and numerical
Monte-Carlo experiments, we find that in records where transient atmospheric processes dominate,
the persistence of natural volumetric changes is underestimated. If each component is assessed
separately, natural centennial trends are locally up to 0.5 mm/yr larger than in case of an integrated
assessment. This implies that external trends in regional MSL rise related to anthropogenic forcing
might be generally overestimated. By applying our approach to a spatially homogeneous centennial
ocean reanalysis (SODA) in combination with fingerprints of glacial ice melt and hydrology changes, we
estimate maximum natural trends in the order of 1 mm/yr for the global average. This value is larger
than previous estimates, but consistent with recent paleo evidence from periods in which the
anthropogenic contribution was absent. Comparing our estimate to the available reconstructions of
20th century global MSL rise of 1.3-2.0 mm/yr suggests a minimum external contribution of at least
0.3 mm/yr. We conclude that an accurate detection of anthropogenic footprints in global and regional
MSL rise requires a more careful assessment of the persistence of intrinsic natural variability.
Posters
Regional Sea Level change in the North Sea since 1900. Frauke Albrecht, Saskia Esselborn, Ralf
Weisse
The regional mean sea level of the North Sea is investigated. Variability in both time and space are
analysed for the period 1900-2012. The sea level is reconstructed using the approach presented in
Church et al. (2004)*. That is tide gauge and altimetry data are combined using the advantage of each
dataset. The length of the tide gauge data is combined with the spatial distribution of the altimetry
data using an EOF-analysis. The analysis considers yearly means of 14 GIA corrected tide gauges, which
are equally distributed over the region. For the altimetry data yearly means of Topex, Jason-1 and
Jason-2 data are used. The altimetry data covers the area 4°W-9°E, 51°N-60°N with a resolution is 0.5°x
0.5°. No inverse barometer correction has been applied.
The quality of the reconstruction is validated against the altimeter data. The patterns of the spatial
variability are well reconstructed. The spatial correlation for the period 1993-2012 is in general very
good (0.6) with exceptions in the southwest and northwest, where the values are a bit lower. The linear
trend of the time period 1993-2012 shows the general pattern of the altimetry data, but an
overestimation especially in the German Bight and along the Danish coast can be seen. The spatial
mean of the reconstruction is compared to earlier reconstructions of this area. Its linear trend for the
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period 1900-2012 is 1.2mm/yr. This value is a bit lower than reconstructions of the same area only
using tide gauge data, which might be due to the relatively few tide gauge data used or the reduced
variability of the time series, which is a byproduct of the method.
Additionally hindcast dataset CoastDat is included in the analysis. It contains wind and the inverse
barometric effect from 1948-2012. This data has been subtracted from the tide gauge and altimetry
data in order to analyse how much the linear trend is influenced by the meteorological signal.
*Church, J.A., White N.J., Coleman R., Lambeck K., and Mitrovica J.X. (2004) Estimates of the regional
distribution of sea-level rise over the 1950 to 2000 period, J. Clim., 17, 2609–2625.
Sea level trends and long-term variability in the South China Sea. A.M. Amiruddin, I.D. Haigh, M.N.
Tsimplis, F.M. Calafat and S. Dangendorf
During the last two decades, sea level rise around the South China Sea (SCS) is nearly three times of
the global mean rate. Due to the economic importance and high density population, rising sea levels
will severely threaten this region. Here, inter-annual variability and longer-term trends in mean sea
level in the SCS have been examined using satellite altimetry data and tide gauge records, along with
steric and meteorological data. Relative sea level trends from tide gauge records longer than 40 years
range between –0.5 ± 0.2 mm/yr and 5.4 ± 0.4 mm/yr. The contribution of atmospheric pressure
changes to sea level trends at the tide gauges is statistically non-significant. For the period 1993-2012,
the basin average sea level rise obtained from altimetry data is 4.8 ± 1.2 mm/yr. The trend is larger in
the Philippines Sea with maximum values reaching 9.9 ± 2.1 mm/yr. Steric trends (1993-2012)
computed down to 1500 m depth, explains a large fraction of the observed trends in most parts of the
Philippines Sea with values as large as 7.5 ± 2.2 mm/yr. Using regional indices from the tide gauge
records, the first and second Empirical Orthogonal Function (EOF) explains 80% and 12% of the
variance, respectively. The first EOF is closely related to the El Niño Southern Oscillation (ENSO) while
the second EOF is associated with the Indian Ocean Dipole (IOD). Inter-annual sea level variability,
especially in the Philippines Sea and the Malacca Strait, can be partly explained by the influence of
ENSO. A considerable part of the variability in the Malacca Strait and off the southern coast of Vietnam
is found to be linked with the IOD. The strength of the link between inter-annual sea level variability
and these climate indices as measured by correlation varies over time. Further research will assess the
decadal variability and their forcing mechanism.
Altimetric sea level variation and reconstruction in the Arctic. Ole B. Andersen, P. Limkilde
Svendsen, A. Aasbjerg and P. Knudsen
The Arctic is still extremely challenging region for the use of remote sensing for ocean studies and
particularly satellite altimetry. One is the fact that despite 20 years of altimetry only very limited sea
level observations exists in the interior of the Arctic Ocean. By carefully reprocessing and re-editing
conventional altimetry from ERS-1/ERS-2 and Envisat we have been able to derive a multi-decade time
series containing far more data in the interior of the Arctic Ocean than ever before, by furthermore
adding in 3 years of Cryosat-2 SAR data quantified as either Lead or Ocean data within the Cryosat-2
SAR mask in the Arctic Ocean we can further extend the time series to more than 20 years. Good
altimetric data is seen to crucial for sea level studies and profoundly for sea level reconstruction where
we present a 60 years sea level reconstruction based on this new data set.
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We here present a new multi-decade altimetric dataset and a 60 year reconstruction of sea level based
on this together with tide gauge information. We also highlight the importance of careful editing of
tide gauges in the Arctic where many tide gauges are more representative of river variations than
actual sea level variations.
On the causes of the differential mean sea level variations between the northern and southern
hemispheres of the Earth. Yuri Barkin, José M. Ferrándiz, Isabel Vigo, David García
In the last decades, satellite altimetry has provided sea level data more densely distributed in space
and time, with the consequent improvement of information with respect to the sea level observation
series from historical tide gauge records. It is well known that sea level does not rise (or fall) uniformly
all over the oceans, but follow complex patterns in space and time. Among the attempts of gathering
the observed behaviour in few intuitive parameters, a candidate to consider are the variations
restricted to some large chosen oceanic areas. Several studies have shown, e.g. differences in the
secular trend of sea level variations between the northern and southern hemispheres of the Earth. In
2011 Barkin pointed an averaged trend of about 2.45 ± 0.32 mm / year sea level rise in the northern
hemisphere, in contrast to a much lower average rate of 0.67 ± 0.30 mm / yr in the southern one. That
estimation showed a clear difference of 1.78 mm / year between the N/S hemispherical rates of sea
level change. It is in good agreement with more recent determinations obtained from the coastal tide
gauge observations, like those reported by Woppelman et al. in 2014, which included corrections for
the vertical geodetic displacements of the stations.
That observed behaviour has not been fully explained yet. Among the potential causes, we analyze the
effects of the changes of the gravitational attraction of the core, which is not invariant but experiences
changes of various reported origins. Among them, we consider here the shifting with respect to the
centre of mass of the whole Earth, which was suggested by Barkin et al in 2008 and treated later in
2011. In that previous work it was shown that the displacement of the core relative to the mantle
would generate a slow tide of inner origin, asymmetric with respect to the equator and thus
redistributing the oceanic and atmospheric masses between the southern and the northern
hemispheres. This dynamical effect can contribute to driving the observed distinct behaviour of mean
sea level rates between the opposite northern and southern hemispheres and even to be a leading
mechanism to an extent that must be assessed.
Along with the fundamental core of the tide, we consider other phenomena that can produce secular
changes in sea level. Factors as e.g. the role of the asymmetric arrangement of the continents in
relation to the northern and southern hemispheres, and the ocean volume and its thermal expansion,
have been also invoked in the literature as potential sources of differences in the regional behaviour
of sea level variations.
Sea level reconstruction from satellite altimetry and tide gauges using advanced signal
decomposition techniques. Sandra-Esther Brunnabend, Jürgen Kusche, Roelof Rietbroek, and
Ehsan Forootan
Satellite altimetry and tide gauge records are used in many studies for the reconstruction of global
mean sea level and regional mean sea level. Most of them used the method of empirical orthogonal
functions (EOF) to reduce noise and investigate the different signals in climate time series. However,
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EOFs have some limitations, e.g. the method falls short of isolating physical signals, limiting the ability
to separate individual modes of sea level variations. In addition, the physical interpretation of the
derived modes is limited because the EOF method assumes different modes to be orthogonal and
consequently uncorrelated, which is not necessarily true for physical signals.
Therefore, we investigate the use of more advanced signal decomposition techniques such as Rotated
EOFs (REOFs), Independent Component Analysis (ICA), and their complex extensions to reconstruct
global and regional sea level change from altimetry data. We anticipate that these methods better
characterize independent physical processes in ocean dynamics as they uses higher than second-order
moments of the probability density function derived from available sea level records. The complex
extensions provide the opportunity to deal with the non-stationary behavior of sea level change. First
results will be compared with sea level estimates derived from ocean modeling and sea level forward
modeling.
Quality control and validation of the new IOP and GOP ocean products from CryoSat-2. Francisco
M. Calafat, Paolo Cipollini, Helen Snaith, Jérôme Bouffard, Pierre Féménias, Tommaso Parrinello
CryoSat-2 is a huge asset to the oceanographic community, and the exploitation of its data over the
ocean represents a welcome additional return for ESA’s investment in a mission whose primary
objective is to monitor the cryosphere. The CryoSat Project has approved, in the frame of the CryoSat
routine phase, the generation of additional ocean products which are available since April 2014. These
are the Interim Ocean Products (IOP), normally available within 2-3 day from acquisition, and the
Geophysical Ocean Products (GOP), with consolidated orbits and available 30 days after acquisition.
To enable their full exploitation by the scientific and operational oceanographic communities, these
new ocean products need to be thoroughly quality-controlled and validated. Here we present the
results of the scientific quality control performed at the UK National Oceanography Centre (NOC)
within the framework of the CryOcean-QCV project. The assessment and quality control of the data is
conducted both daily and monthly on a global scale for the L2 IOP and GOP products and includes
coverage/completeness, data flow and latency analysis, along-track and crossover analysis, and
estimation of error levels and measurement precision. Diagnostics are computed for the sea surface
height (SSH), significant wave height (SWH), radar backscatter coefficient (sigma0), wind speed and
mispointing parameters.
In addition we present an absolute validation of the altimetric SSH for the GOP product against sea
level observations from high-quality tide gauges equipped with Global Positioning System (GPS)
receivers. Finally, the validation is extended by comparing the SSH from CryoSat-2 with that from other
altimetric missions (e.g. Jason-2).
Coastal sea level measurements and trends from improved satellite altimetry. Paolo Cipollini,
Francisco M. Calafat, David Cotton, Marcello Passaro, Helen Snaith
Satellite altimetry in the coastal zone has improved significantly in recent years, thanks to the
dedicated efforts of a large community of researchers worldwide. More and better measurements of
sea level (and significant wave height) are recovered thanks to improved waveform processing
(retracking) and corrections, as showcased at the annual workshops of the coastal altimetry
community (http://www.coastalt.eu/community). In this contribution, after a concise review of the
advances in coastal altimetry, we present results on coastal altimetry activities being carried out at
NOC.
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Within the ESA Climate Change Initiative Sea Level Project we have first quantified the user
requirements in terms of accuracy and long-term stability in the coastal domain. We will present and
discuss the findings – for instance long-term stability requirements of 0.5–1.0 mm/y at regional level
and of 0.2–0.5 mm/y for a ‘global coastal’ mean linking the global estimates of sea level rise from openocean altimetry with the Tide Gauges. We will also describe work on screening and filtering of the highrate altimetric data and the atmospheric and geophysical corrections in the coastal zone, and the
assessment of coastal retrackers showing the improvements from the sub-waveform approach
adopted in the ALES retracker (Passaro et al., Rem. Sens. Env, 2014) in comparison with a number of
well-monitored and quality-controlled tide gauges.
In a demonstration project funded by the UK Space Agency, Sea Level SpaceWatch, we have computed
the latest figures on observed sea level around the UK (rolling annual mean sea level, the amplitude of
the annual cycle and both the annual-scale trend and decadal-scale trend) from the Envisat/AltiKa
altimeter series, and compared them with selected Tide Gauges. We will show the results of this
validation and discuss the potential transition towards an operational sea level advice service aimed
at supporting long term planning and risk management.
Impact of large-scale climate patterns on sea-level variability in the Gulf of Guinea with focus on
Ghana. Evadzi, P., Hünicke, B., Zorita, E.
The analysis of sea-level variability along West Africa has been hampered by the limited length and
quality of tide-gauge records. Ghana is the only country along the West African coast with relatively
long sea-level records available.
In this study we aim on characterizing the large-scale climate forcing that drive mean sea-level
variability at and off the coast of Ghana and study its decadal variability and long-term trends in the
observational period.
For this purpose, available sea-level information (referred from tide gauges, satellite altimetry, gridded
reconstructions and ocean model simulations) will be statistically analyzed together with
meteorological data from reanalysis products and climate model simulations. The main large-scale
climate factors driving regional mean sea level at these timescales will be identified and quantified.
Variation of sea level and net water flux in the Mediterranean Sea. Luciana Fenoglio-Marc
The sea level, the mass-induced sea level variability and the net mass transport between
Mediterranean Sea and the Atlantic Ocean are derived in the interval 2002-2014 from tide gauges and
satellite-based observations. In the interval 1960-2014 they are obtained by combining multiple
observational datasets and results from a regional climate model simulation.
The decadal variation in mass is the main contributor to the sea level variability in the Mediterranean
Sea and appears to be related to changes in the Atlantic Ocean. The decadal variations in net
evaporation at the sea-surface, such as the increase since 1970, drive the changes in net inflow at
Gibraltar.
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Compared to previous analysis, at basin scale an improved agreement between sea level observed by
altimetry and derived from the steric-corrected GRACE data is found using sea level data of the ESA
Climate Change Initiative (CCI) and release 5 of the GRACE data.
At spatial scales the improved GRACE data and filters reduce the hydrological leakage giving a better
agreement between the components.
Time-varying trends in regional sea level from tide gauge data. Thomas Frederikse, Riccardo Riva,
Cornelis Slobbe, Taco Broerse, Martin Verlaan
Knowledge and understanding of contemporary changes is necessary to better predict future sea level
rise, and one of the primary observational datasets is represented by tide gauge records. We propose
a new method to estimate trends from tide gauge data by using a state space formulation, which
couples the direct observations to a predefined state space model by using a Kalman filter. The model
consists of a time-varying trend and seasonal cycle, and variability induced by several physical
processes, such as wind, atmospheric pressure changes and teleconnection patterns. This model has
two advantages over the classical least-squares method that uses regression to explain variations due
to known processes: it can account for variations in phase and amplitude of the seasonal cycle, and it
allows the trend to vary over time. This time-varying trend consists of a secular trend and lowfrequency variance that is not explained by any other term in the model. As a test case, we have used
tide gauge data from stations around the North Sea over the period 1980-2013: the time-varying trend
clearly shows a large decadal variability. To validate whether this model is correctly explaining the
observed variance, we have compared our results against time-series where the variability has been
predicted by the Dutch Continental Shelf Model (DCSM), a 2-dimensional storm surge model that
estimates the effects of wind, pressure and tides. Trends obtained from the DCSM-corrected run show
patterns at inter-annual and decadal scales that are very similar to the trends obtained with the state
space model. The mean trends over the period 1980-2013 are also very similar for both models, but
there are significant differences when these estimates are compared to results from a classical leastsquares analysis.
Scientific roadmap towards height system unification with GOCE. Th. Gruber, R. Rummel, M.
Sideris, E. Rangelova, P. Woodworth, C. Hughes, J. Ihde, G. Liebsch, A. Rülke, Ch. Gerlach, R.
Haagmans
GOCE allows the determination of geoid heights with an accuracy of 1-2cm and spatial resolution of at
least 100 km globally. An important application that will benefit from this is the global unification of
the (over 100) existing height systems and consequently the comparability of sea level records
attached to them. GOCE will provide three important components of height unification: highly
accurate potential differences (geopotential numbers), a global geoid- or quasi-geoid-based reference
surface for elevations that will be independent of inaccuracies and inconsistencies of local and regional
data, and a consistent way to refer to the same datum all the relevant gravimetric, topographic and
oceanographic data. The paper summarizes results of a project supported by the European Space
Agency and specifies a scientific roadmap on how GOCE can support world height system unification.
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The Various of Wet Tropospheric Corrections effect on the Regional Sea Level Variability in the
Indonesia Seas. Eko Yuli Handoko, Maria Joana Fernandes, Clara Lazaro
For more than 20 years, satellite altimetry has been observing sea level variability over the world. The
study of sea level variation in Indonesia region using satellite altimetry is a challenging topic due to the
coastal effects present in altimeter data, which need to be addressed. Amongst these effects, the wet
tropospheric correction (WTC) is of particular relevance due to its large spatio-temporal variation.
The aim of this research is to assess the impacts of various WTC in the determination of sea level
change in Indonesia.
Due to its high temporal and spatial variability, the wet tropospheric correction is one of the major
error sources in coastal altimetry. GNSS-derived path delay (GPD) is an algorithm to estimate the wet
tropospheric correction which combines zenith wet delays (ZWD) derived from GNSS, valid microwave
radiometer (MWR) measurements and atmospheric models. Global GPD solutions have been derived
by University of Porto for the main altimetry missions (ERS-1, ERS-2, Envisat, TOPEX/Poseidon, Jason1, Jason-2, CryoSat-2 and SARAL/AltiKa) using more than 400 GNSS stations in coastal and island
regions. In particular, a local network of near 30 GNSS stations, located mostly along of the Sumatera
Island, has been used to improve the GNSS coverage in the Indonesian region.
In view to determine the most suitable corrections, in this research we present an assessment of the
effect of using these different WTC on sea level studies in the Indonesia region using statistical analysis
of SLA variance function of distance from coast and comparisons with ZTD from GNSS stations not used
in the estimation of the GPD and DComb corrections. Finally, the sea level time series for the period
1992-2013, computed using the selected set of WTC is presented and compared with series
determined using less accurate corrections
Ocean Bottom Pressure Records at the Permanent Service for Mean Sea Level. Angela Hibbert,
Andrew Matthews, Chris W. Hughes, Mark E. Tamisiea
As part of a research effort funded by the U.K. Natural Environment Research Council, the Permanent
Service for Mean Sea Level (PSMSL) has been developing a repository of data from in-situ ocean
bottom pressure recorders (OBPRs) from all possible sources. The data are being processed to a
common format using a consistent methodology so that time series are directly comparable. Efforts
are also being made to ensure that data are accompanied by comprehensive metadata. The OBPR
data are supplied primarily for hourly and daily intervals, making them ideal for studies of tidal to
seasonal variability. In addition, because bottom pressure recorders measure changes in ocean mass,
these data are an ideal complement to GRACE satellite data and a useful accompaniment to sea level
data from tide gauges and altimetry. Consequently, it is anticipated that the PSMSL OBPR repository
will become a valuable product to the scientific community
The Semiannual Oscillation of Southern Ocean Sea Level. Angela Hibbert, Harry Leach, Phil
Woodworth
The atmospheric Semiannual Oscillation (SAO) is a half-yearly wave in mean sea level air pressure,
which exhibits equinoctial maxima between 45°S and 50°S and solstitial maxima between 55°S and
65°s, with a phase reversal occurring at around 60°S. Its existence has been attributed to a phase
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difference in the annual temperature cycle between mid- and high-latitudes which sets up meridional
temperature and pressure gradients that are largest during September and March, enhancing
atmospheric baroclinicity and inducing equinoctial maxima in the Southern Hemisphere Westerlies.
In this study, we use harmonic analysis of atmospheric and oceanic Southern Ocean datasets to show
that this atmospheric SAO induces oceanic counterparts in sea level and circumpolar transport. This
aspect of atmosphere–ocean interaction is particularly important, given the capacity of the Antarctic
Circumpolar Current (ACC) to influence regional climate through the exchange of heat, fresh water and
nutrients to each of the major ocean basins. We examine the relative contributions of local and
regional semiannual atmospheric fluctuations as well as the individual influences of atmospheric
pressure and zonal winds in explaining the observed sea level response at Southern Ocean and South
Atlantic tide gauge stations and in altimetry data.
Celebrating 30 Years of the South Atlantic Tide Gauge Network. Angela Hibbert, Pete Foden, Jeff
Pugh, Geoff Hargreaves, Steve Mack, Phil Woodworth
It is now 30 Years since NOC Liverpool’s South Atlantic Network came into being (in 1985); at what was
the Institute of Oceanographic Sciences, Bidston. In this poster, we present some of the scientific and
technological advances that have originated from the Network, such as improved understanding of
ACC variability and the development of tide gauge instrumentation to facilitate accurate datum
control. We describe the scientific products currently afforded by the South Atlantic Network and how
they form an important part of the UK contribution to the IOC’s Global Sea Level Observing System
(GLOSS). Finally, we outline proposals for further technological and scientific development of the
Network, including plans to improve the resilience of tide gauge technology in hostile and/or remote
locations.
Observed changes and variability of mean sea-level in the Baltic Sea region during the last 200
years –a review. Birgit Hünicke,l Eduardo Zorita
The understanding of the processes driving future trends in sea level presumes an understanding of
long-term variability in the observational period. This requires an accurate assessment of past and
recent change in global and regional sea-level. Recent sea-level trends and decadal variations display
large regional contrasts due to the different physical mechanisms that affect sea level. The Baltic Sea
area, with its complex shoreline, its exposure to the energetic North Atlantic weather and its proximity
to the recent glacial ice-sheets (GIA), provides a challenging research field that requires the
collaboration of multiple scientific disciplines. Baltic Sea level variability is caused by different climatic
and geological factors that render their understanding more difficult than for other areas of the Earth.
Yet this understanding is crucial to predict with reliability the sea-level rise in the Baltic Sea that will
be brought about by anthropogenic climate change.
Here, we present observed changes in mean sea-level variability and the main (climate) drivers for
these changes during the last 200 years by updating and discussing results described in the framework
of the BACC2 project (2nd BALTEX Assessment of Climate Change for the Baltic Sea Basin).
Baltic Sea level measured relative to land display a strong fingerprint of the GIA effect with sea level
falling by up to 8.2 mm year−1 in the northern parts and slightly rising in parts of the southern Baltic
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coasts. Estimates of absolute rise in mean sea-level lie within the range of recent global estimates (1.3–
1.8 mm year−1). The 30-year trends of Baltic Sea tide gauge records tend to increase, but similar or
even slightly higher rates were observed around 1900 and 1950. Baltic Sea level shows higher values
during winter and lower values during spring and this seasonal amplitude increased between 1800 and
2000.
This work is part of the Baltic Earth program (www.baltic-earth.eu) and contributes to the Baltic Earth
Grand Challenge ‘Understanding sea level dynamics in the Baltic Sea’.
Variability of decadal sea-level trends in the Baltic Sea. Sitar Karabil, Eduardo Zorita, Birgit
Huenicke
We analysed the variability of the linear decadal sea-level trends in the Baltic Sea over the past 100
years and their connections to trends in the sea-level-pressure (SLP) field. The analysis is limited to the
December-to-February season. We use means of tide gauges from the Permanent Service for Mean
sea level and monthly gridded Sea Level Pressure (SLP) covering the North Atlantic/European sector
from the University of Colorado. To select the tide gauges, we took into account the geographical
distribution and record length retaining Helsinki, Ratan, Stockholm, Kungsholmsfort, Smogen,
Travemunde, Wismar, Warnemunde and Klaipeda. The linear decadal trends were calculated over
gliding 11-year windows of the tide gauges and the SLP grid records. After computing the decadal
gliding trends, we focused on the correlation patterns between each individual tide gauge and the SLP
for every grid separately.
The results show that the tide gauges can be classified into two groups according to their correlation
with the SLP trends. Helsinki, Ratan, Stockholm, Kungsholmsfort, Smogen and Klaipeda display
resembling correlation patterns that have high positive correlation at the south and negative
correlation at the north, with the zero line approximately located at 50 N, and is thus similar to the
typical pattern of the North Atlantic Oscillation. However, Travemunde, Wismar and Warnemunde,
which are located at the southern Baltic Sea coast, display a rather different pattern that shows
negative correlations over the Baltic Sea region, and negligible correlations elsewhere.
The main implication of this study is that the estimation of the possible acceleration of sea-level and
of its statistical significance has to take into account that the variability of decadal sea-level trends
seems to be controlled by very different atmospheric circulation factors, even in this small region.
Forcing of Global Mean Sea Level Interannual variability for the period 1950-2010. Gabriel Jordà,
Francisco Mir Calafat, Mikis Tsimplis
Lots of attention has been paid to the forcing of global mean sea level (GMSL) multidecadal and
centennial trends. Conversely, the forcing of GMSL at interannual scales have received less attention,
specially for the pre-altimetric period. In this work we have used a new GMSL reconstruction that
covers the whole XX century and shows high skills in the representation of interannual variability to
investigate the mechanisms forcing GMSL interannual variability. The different components of GMSL
have been estimated from different observational based datasets. Our results suggest that the main
driving mechanism is the transfer of water from land to the ocean through changes in the hydrological
cycle. The second driving mechanism is thermal expansion while the storage of water in the
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atmosphere barely contributes. The results also show that there is no particular continent dominating
the changes in land water storage at interannual scale. Finally, some discussion about the reliability of
different databases will be presented.
Nordic Sea Level – Analysis of PSMSL RLR Tide Gauge data. Per Knudsen, Ole Andersen, Carlo
Sørensen
Tide gauge data from the Nordic region covering a period of time from 1920 to 2000 are evaluated. 63
stations having RLR data for at least 40 years have been used. Each tide gauge data record was
averaged to annual averages after the monthly average seasonal anomalies were removed.
Some stations lack data, especially before around 1950. Hence, to compute representative sea level
trends for the 1920-2000 period a procedure for filling in estimated sea level values in the voids, is
needed.
To fill in voids in the tide gauge data records a reconstruction method was applied that utilizes EOF.s
in an iterative manner. Subsequently the trends were computed. The estimated trends range from
about -8 mm/year to 2 mm/year reflecting both post-glacial uplift and sea level rise.
An evaluation of the first EOFs show that the first EOF clearly describes the trends in the time series.
EOF #2 and #3 describe differences in the inter-annual sea level variability with-in the Baltic Sea and
differences between the Baltic and the North Atlantic / Norwegian seas, respectively.
Variability of the ocean bottom pressure along the Gulf of Cadiz and its effect on the sea level
spatial distribution. Irene Laiz, Marta Marcos, Jesús Gómez-Enri, Evan Mason, Begoña Tejedor,
Alazne Aboitiz, Pilar Villares
A high resolution regional ocean model (Regional Ocean Modeling System, ROMS) was used to explore
the spatial patterns of bottom pressure anomalies within the Gulf of Cadiz as a function of depth and
time together with a simple conceptual model that relates temperature changes to bottom pressure
variations. Moreover, daily maps of gridded altimeter-derived sea level anomalies were used to
analyze how the bottom pressure variations at depths below and above the steric anomalies can affect
the sea level spatial distribution at regional scales.
Satellite altimetry Calibration/Validation at the Australian Bass Strait site in the context of the
new missions Jason-3 and Sentinel-3. Legresy B., C. Watson, J. Church, N. White, J. Beardsley, J.
Andrewartha
The Bass Strait satellite altimetry validation site has been one of 3 reference sites spread around the
world for the Topex-Poseidon and Jason satellite altimeter series since the 1990s. There, the absolute
calibration attained is at the cm level contributing importantly to the altimetry systems absolute bias
estimation and to their drifts monitoring.
In 2015-2016 two new accurate satellite altimetry missions will be launched and need calibration
validation. The method developed over the years for Jason involves tide gauges, moorings where we
measure temperature, salinity, pressure and currents, atmospheric measurements and operational
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models (ACCESS) to extend measurements and corrections from coastal tide gauges to the cal/val site
25km off the coast under the satellite track. GPS buoys are regularly deployed to reference the in situ
sea level measurements to the same datum as the satellites and estimate instruments bias and drifts.
While the system is quite operational in view of the Jason-3 satellite, the newcomer Sentinel-3 will
have a different ground track, repeat time, and measurement mode. We will show the overall
calibration system and the results over the TOPEX-Jason period. We will also show the extension and
improvements we are developing in the frame of Jason-3 and Sentinel-3 new missions. In particular,
we investigate the possibility and capability of a regional ocean model to test the sensitivity and extend
the present system with a mooring under the Jason track to a Sentinel-3a crossover ~10km away.
Sensitivity of sea-level rise reconstruction from 1900 to present. Legresy B. , J. Church , N. White,
D. Monselesan and A. Slangen
We reconstruct the sea level rise from 1900 to present, revisiting the reconstruction from Church and
White (2011). We update this reconstruction, which is based on satellite altimetry learning and
projects tide gauges records on the derived modes of variability. We performed or repeated a number
of sensitivity tests on the learning period, number of modes, and inversion parameters. We also tested
the sensitivity to variations in the mathematical method, in the learning process as well as the number
of tide gauges, vertical crustal movement and contemporary mass load redistribution at the surface of
the Earth. For global mean sea level, the length of the learning period seems to be of little importance
beyond one decade. The same applies, for example, to the number of modes, it does not improve the
solution to use more than 4 modes for the longer records of global mean sea level. We show sensitivity
results for the long term global mean sea level and for regional mean sea level over the 1950-2015
period. We revisit the error budget. Finally, we compare to other reconstructions in view of this
sensitivity analysis.
Relative sea-level change along the Italian coast during the late Holocene and projections for
2100: Coastal plain impacts based on high-resolution DTMs and geodetic data. Valeria Lo Presti.,
Fabrizio Antonioli , Alessandro Amorosi , Marco Anzidei , Gianni De Falco , Alessandro Fontana ,
Giuseppe Fontolan , Giuseppe Mastronuzzi , Enrico Serpelloni , Antonio Vecchio
Sea-level data are used to provide projections of sea-level change in Italy for the year 2100 by adding
isostatic and vertical tectonic components to the IPCC 2013 and Rahmstorf projections. We focus on
the North Adriatic coast and Venice, subsiding at -0.7 mm\yr, the tectonically stable Cagliari and
Oristano coastal Plain (Sardinia) and the slightly uplifting area of Mar Piccolo (Taranto, Apulia). We
used high-resolution DTMs to depict a multitemporal flooding scenario up to 2100.
Data of sea level indicators are compared with the predicted sea-level curves providing estimates of
the vertical tectonic contribution to the relative sea-level change. The results are based on the most
recent ANU model and discussed against available GPS data for present day vertical land motion and
sea level trend from tide gauge data. On the basis of eustatic, tectonic and isostatic components to
sea-level change, projections are offered for those coastal plains currently placed at elevations very
close to present-day sea level.
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Sea Level Oscillations in The Baltic Sea: From Minutes to Centuries. Igor P. Medvedev, Alexander
B. Rabinovich, Evgueni A. Kulikov
Various types of processes determine sea level changes in the Baltic Sea: tectonic motions, multiyear
climatic variations, the pole tide, seasonal oscillations, tides, storm surges and seiches. We examined
the formation mechanisms and basic properties of each of these oscillations covering a wide range of
periods: from minutes to centuries. The Baltic Sea is connected to the North Sea and Atlantic Ocean
through narrow and shallow Danish straits, which act as a low-pass filter, strongly suppressing highfrequency processes but allowing low-frequency processes to pass freely through. As a result, relatively
short-period oscillations (with periods 3-4 months) are induced by the waves coming from the North
Sea. Tides, storm surges and seiches are of the first type and have a character of “proper oscillations”;
they are formed in the Baltic Sea as a whole, or gulfs and bays of the sea. Similar formation mechanisms
of these processes lead to strong similarity in their physical properties. Different types of oscillations
superimpose and interact with each other. In particular, seiches increase the storm surge heights at
the head of the Gulf of Finland; the fundamental eigen mode of this gulf, with a period of ~27 hrs, is
the main reason for catastrophic Saint Petersburg floods and amplification of diurnal tidal constituents.
Radiational tides appear to play an essential role is some parts of the sea, including Narva and
Daugavgriva; moreover, in Curonian Lagoon astronomical (gravitational) tides are not observed at all,
while the radiational tide caused by the sea breeze, is substantial. Climatic fluctuations, seasonal sea
level oscillations and the pole tide are all “induced oscillations”. They have very similar spatial structure
and are found to be strongly influenced by atmospheric processes over the Northeast Atlantic.
Tides in the Baltic, Black and Caspian Seas. Igor P. Medvedev, Alexander B. Rabinovich, Evgueni A.
Kulikov
Tides are the main type of sea level variability in the World Ocean. However, tidal signal from the World
Ocean almost do not penetrate into isolated inland seas, such as the Black, Caspian and Baltic seas.
Consequently, only the directly forced tides are formed in these seas. Tides are weak in these seas in
comparison with the longwave background noise; thus long observation time series are necessary to
estimate tidal constituents precisely. Such particular series were used in these studies: up to 123 years
in the Baltic Sea, and up to 38 years in the Black and Caspian seas. High-resolution spectral analysis
revealed fine structure of well-defined spectral peaks at tidal frequencies. Diurnal radiational tidal
constituent S1 (1 cpd) and high-frequency radiational tidal peaks, multiples of a solar day (3, 4, 5, 6
and 8 cpd), were identified in some areas of the seas. Sea-breeze winds are supposed to be the main
factor inducing these oscillations. Harmonic analysis of tides for individual yearly series with
consecutive vector averaging over the entire observational period was applied to estimate mean
amplitudes and phases of major tidal constituents, the maximum tidal height, the type of tides and the
spatial structure of tides. Eigen oscillations of the respective basins (sea seiche modes), with periods
close to diurnal and semidiurnal, play the key role in formation of the corresponding tides.
Comparing coastal and open ocean sea level variability and trend from altimetric data. A. Melet,
M. Nonti, B. Chide, B. Meyssignac, F. Birol
Since 1993, altimetry has provided an unprecedented opportunity to study sea level variability with a
quasi-global coverage. Satellite altimetry indicates that sea level has been rising fast in response to
global warming, but with large regional variations. However, standard altimetric data do not allow to
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study sea level variability and rise close to the coast, where the socio-economic impacts of sea level
rise are the greatest. Recently, along-track altimetric data have been reprocessed at LEGOS/CTOH
using algorithms adapted to coastal regions to recover information in coastal zones (this reprocessed
coastal product is referred to as the XTRACK dataset here).
In this study, we first intercalibrate the along-track Topex-Poséidon, Jason-1 and Jason-2 XTRACK
dataset to that distributed by AVISO to have consistent sea level data in the open ocean. Then, sea
level trends are computed with the XTRACK dataset to analyse how sea level rise varies as a function
of the distance to the coast. Spectral analyses are performed to assess the frequency bands for which
coastal sea level variability and open ocean variability differ.
Analyses are performed over two regions (West coast of Africa and southwest Pacific). They will be
extended to the global ocean to provide a map of sea level trends over the 1993-2012 period for the
coastal zones of the global ocean.
Global and Regional Sea Level Change Over the 20th Century: How Can it Inform Us About the
21st Century?. R. S. Nerem, B. D. Hamlington, F. Landerer, R. Leben, and J. Willis
Tide gauges, satellite altimetry, satellite gravity, and hydrography provide a rich set of measurements
from which to understand natural and anthropogenic sea level variations over the 20th century. These
observations can help partition the contributions from thermal expansion, the melting of ice, changes
in land water storage, and a variety of other sources, and also help understand the regional variations
from global average sea level change. However, the satellite observations only cover the last decade
or two and so understanding the long-term record of 20th century sea level change is challenging due
to the presence of decadal variability. We will review the observational record and discuss the impacts
on global and regional sea level change over the 20th century, including the impacts of climate
variability (ENSO, PDO, etc.). We will discuss the implications of the this record for projecting future
global and regional sea level change over the 21st century and what the limiting error sources and
challenges are.
Global Sea Level rise from an Empirical Mode Decomposition perspective. Marco Olivieri, Giorgio
Spada, Gaia Galassi
Empirical Mode Decomposition (EMD) is a state-of-the-art technique for the analysis of non-linear time
series, which allows for a recursive separation of a limited number of oscillating components from a
long-term “trend”. The EMD approach does not require constraints on the frequency content of the
oscillating terms nor on the shape of the trend, which in traditional statistical analyses has an a-priori
polynomial form. This appears to be powerful when, as for the case of tide gauge data, the frequency
content is complex and not stationary. We have applied the EMD method to the entire dataset of RLR
(Revised Local Reference) tide gauge time-series archived at the PSMSL (Permanent Service for Mean
Sea Level), with the aim of assessing the long term trend of sea-level rise and of separating it from
decadal and multi-decadal oscillations. We provide a new model for the global sea-level variation at
global and regional scale, in terms trend and acceleration. Our analysis also focuses on the possible
existence of a ~60 years oscillation in long-term sea level.
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The Annual Global-Mean Thermosteric Height Budget. Christopher G. Piecuch, Rui M. Ponte
Changes in global-mean thermosteric height (GMTH) reflect expansion or contraction of the oceans
due to thermally induced ocean density changes. While past works diagnose GMTH changes using in
situ data or remote measurements, understanding of physical processes contributing to the GMTH
changes is lacking. Unlike heat, density (or buoyancy) is not conserved in the ocean—a consequence
of the nonlinear nature of the seawater equation of state. While GMTH can be affected by surface heat
fluxes, it can also be influenced by net creation or destruction of buoyancy by ocean heat transports
across constant-pressure and -temperature surfaces.
To investigate the annual GMTH budget, we first perform comprehensive diagnostics of the ECCOProduction Release 1 ocean state estimate. Estimated annual GMTH changes are wholly compensated
by net surface buoyancy flux (NSBF) due to surface heat exchange. Ocean heat transports do not
contribute mainly because annual ocean heat content anomalies are mostly stored in the upper ocean
(and are not transported along strong temperature gradients). These results suggest that, for the
annual frequency, the GMTH budget can be diagnosed observationally from knowledge of the
temperature and NSBF fields. To corroborate these findings, and also to gauge the consistency of
available datasets, we compare to GMTH and NSBF annual cycles computed based on different
observational products. The amplitude and phase of annual cycle in GMTH derived from Argo gridded
data are nearly indistinguishable from those derived from NSBF based on OAFlux surface heat
exchanges, supporting findings from the state estimate. Additional analyses consider annual cycles in
GMTH estimated from altimetry and GRACE, and in NSBF determined from NOCS v2.0 marine surface
fluxes along with satellite sea-surface temperature. Results highlight the usefulness of GMTH as a
measure of the quality of surface flux data.
Deriving sea level from tide gauges. Jens Schröter, Manfred Wenzel, Klaus Grosfeld, Roelof
Rietbroek
Past sea level is frequently derived from tide gauge measurements. A common approach is to relate
relative tide gauge data to geocentric measurements derived from satellite altimetry.
We present two methods on how to relate the different reference frames and what consequences can
be expected from different assumptions about vertical land movements.
The South Atlantic sea level variability. Raisa de Siqueira Alves, Angela Hibbert and Harry Leach
Sea Level varies on different time and spatial scales and due to a large range of forcing processes, such
as tides, weather, the variability described by atmospheric climate modes and ocean processes. In the
South Atlantic ocean, little is known about how the sea level responds to these processes, although
some recent works by Sterl & Hazeleger (2003), Lubbeck et al. (2010) and Nnamchi et al. (2011)
indicate an intrinsic variability in this ocean. Thus, in this project, we aim to assess the contributions of
atmospheric climate modes, sea surface temperature and atmospheric pressure to sea level variation
in this ocean. We used the AVISO combined altimetry dataset from 10/1992 to 01/2011, published
indices of climate modes, atmospheric reanalysis datasets of surface pressure, sea surface
temperature from HadISST and tide gauge data from the PSMSL data base. The altimetry and tide
gauge data were analyzed separately, but using the same methodology. First we divided their time
series into annual cycle and residuals. Then, from the residuals, we calculated the mean sea level trend,
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performed an EOF analysis to characterize the sea level natural modes of variability, correlated them
with the atmospheric indices and corrected the atmospheric pressure and temperature effect. A sea
level dipole was present in the EOF analyses of the tide gauge data and this led us to calculate a new
atmospheric index, called the South Atlantic Index (SAI), to correlate with the sea level variation. As a
result, the SAI, together with the Pacific-South America Mode indices and the Southern Oscillation
Index, were always significantly correlated with the sea level eigenvectors, even after the inverse
barometer and thermal effect correction. The residuals contributed the most to the variance of the
sea level in the South Atlantic, especially near the Confluence Zone and Agulhas Retroflection area.
Yet, this variance was not explained by the pressure or temperature effects studied in this work.
Closing the gap between regional and global sea level in the Bay of Bengal. Bernd Uebbing, Roelof
Rietbroek, Sandra-Esther Brunnabend, Jürgen Kusche
A thorough understanding of sea level rise requires the quantification of the underlying drivers. Using
satellite gravimetry and radar altimetry, we can split up the global mean sea level budget into
components induced by mass changes (e.g. melting of glaciers, ice-sheets and water cycle variations)
and volumetric changes (thermo and halosteric variations). However, global sea level rise does not
necessarily match up with regional estimates of sea level change. This becomes apparent when
regional trend maps of altimetry data or individual tide gauges, are compared with global mean sea
level estimates.
In this study, we use satellite gravimetry from GRACE and radar altimetry from Jason-1 and Jason-2 to
break down the sea level budget in the Bay of Bengal. The data is combined in a joint inversion scheme,
where individual contributions to sea level are parametrized by a set of physically determined a priori
'fingerprints' whose time variations are then estimated from the data.
Regional estimates of total sea level rise in the Bay of Bengal revealed sea level rise of twice the global
rate and are subsequently compared with global estimates and altimetry. Furthermore, we investigate
the individual components from mass and steric sea level. We find that 20% of the total sea level rise
of about 5.8 mm/yr (2002.5-2014.5) in the Bay of Bengal are related to mass changes, while the
remaining 80% are attributed to steric changes. The dominant contribution from the latter in the Bay
of Bengal is confirmed by independent data from ARGO floats, and oceanographic modelling.
How long does it take to measure a trend in ocean bottom pressure?. Joanne Williams, Chris
Hughes, Mark Tamisiea
Ocean bottom pressure, measured at only a few locations, can theoretically be used to derive global
mean mass changes in the ocean. However bottom pressure sensors suffer from non-linear drift, so
cannot currently be used to measure trends. Therefore we investigate an alternative method to
measure the small bottom pressure signal as the difference between the two large signals of steric
pressure (from a hydrographic mooring) and sea-surface height (from altimetry). In many places
bottom pressure has much smaller variability than the corresponding sea-level signal, and so the time
required to detect a trend of given magnitude is much shorter. We test the method on data from the
Rapid mooring array at 26N in the Atlantic, and determine how many years would be required to detect
a trend in bottom pressure from this technique.
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Modelling Sea Level Changes
Oral Presentations
Long-Term Internal Variability Effects on Centennial Dynamic Sea Level Projections. Mohammad
H. Bordbar Thomas Martin, Mojib Latif, Wonsun Park
The Earth’s surface is warming in response to anthropogenic emissions of greenhouse gases, especially
carbon dioxide (CO2). Sea level rise is one of the most pressing aspects of global warming with farreaching consequences for coastal societies. However, sea level rise did and will strongly vary from
coast to coast. Here we investigate the long-term internal variability effects on centennial projections
of dynamic sea level (DSL), the local departure from the globally averaged sea level. A large ensemble
of global warming integrations was conducted with a climate model, where each ensemble member
was forced by identical CO2-increase but started from different atmospheric and oceanic initial
conditions taken from an unforced millennial control run. In large parts of the mid- and high latitudes,
the ensemble spread of the projected centennial DSL trends is of the same order of magnitude as the
globally averaged steric sea level rise, suggesting internal variability cannot be ignored when assessing
21st century DSL changes. This conclusion is also supported by analyzing projections with other climate
models. The ensemble spread is strongly reduced in the mid- to high latitudes if only the atmospheric
initial conditions are perturbed; suggesting uncertainty in the projected centennial DSL trends there
is largely due to the lack of ocean information. Thus climate model projections of regional sea level
would benefit from ocean initialization.
Interannual Predictability of North Atlantic Sea Level Dynamics. Robert Fraser, Laure Zanna, Chris
Wilson
A large degree of uncertainty remains in both the temporal and spatial variability of regional sea level
predictions. This study aims to constrain the uncertainty, due to both the atmospheric and ocean
states, by examining the dynamics and predictability of sea surface height (SSH) in the North Atlantic
on interannual timescales. An evaluation of the typical timescales of SSH predictability in an idealised
model set up of a flat bottomed, barotropic double gyre has been undertaken. Moreover, the
sensitivity of the SSH predictability to applied wind stress perturbations of differing magnitudes has
been examined. The timescales of predictability present were evaluated by using linear inverse
modeling techniques to represent the system by a statistical, yet dynamical, model. It was found that
potential for interannual predictability exists and is largely located both in the jet region and in the
vicinity of the western boundary. In order to investigate the mechanism behind this interannual
variability and predictability, further analysis of the ocean momentum budget was carried out with a
focus on the eddy-mean flow interaction. Results indicate that further studies, where particular
emphasis is placed on sea level anomalies near the coast, could inform measurements by examining
which time and spatial resolutions are needed to obtain relevant measures of predictability
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Seasonal coastal sea-level prediction using a dynamical model. John A. Church, Peter C. McIntosh,
Elaine R. Miles, Ken Ridgway, Claire M. Spillman
Many millions of people living in coastal regions are vulnerable to sea-level extremes resulting from
the combined effect of storm surges, seasonal and interannual sea-level anomalies, and long term sealevel rise. Accurate coastal sea-level predictions would assist in preparing for extreme events. While
sea-level rise has been a major focus of international research, and there are a number of operational
storm surge prediction programs, the influence of interannual and seasonal sea-level anomalies has
received less attention, with statistically-based operational prediction schemes available at only a few
locations in the western Pacific Ocean. Here, we demonstrate that forecasts of coastal sea-level
anomalies from the dynamical Predictive Ocean Atmosphere Model for Australia (POAMA) have
significant skill throughout the equatorial Pacific and along the eastern boundaries of the Pacific and
Indian oceans. POAMA forecasts for the western Pacific have greater skill than statistical forecasts from
both a Markov model and canonical correlation analysis. Our results demonstrate the capability of
POAMA to provide earlier and more skilful warnings of seasonal sea-level changes for vulnerable
coastal communities.
Regional Budgets of Sea Level in the ECCO-Production Release 1 Ocean State Estimate.
Christopher G. Piecuch, Rui M. Ponte, Gael Forget, Ichiro Fukumori
We consider regional sea level from the Estimating the Circulation and Climate of the Ocean (ECCO)Production Release 1 state estimate. The solution is a physically consistent estimate of the global ocean
circulation and ice state over 1992-2011; it incorporates millions of ocean observations into an ocean
general circulation model framework. The consistency of the estimate facilitates decomposition of sea
level into steric-height (density) and bottom-pressure (mass) contributions; it also allows for
unambiguous identification of the physical processes impacting the evolution of steric height and
bottom pressure. Steric anomalies can be ascribed to advection, diffusion, and forcing of heat and salt;
bottom pressure can be partitioned into barotropic and baroclinic components.
We focus on interannual and decadal anomalies. In deep basins at low and middle latitudes, sea level
is controlled by steric height, but bottom pressure contributes at high latitudes and over shelf seas.
Steric anomalies generally reflect a complex interplay between surface forcing and vertical and
horizontal advection and diffusion of heat and salt. Thermosteric variations predominate in the tropical
Pacific and Indian Oceans, whereas halosteric variations are important in polar regions characterized
by sea ice. Vertical heaving controls steric changes only over small parts of the northeastern North
Pacific and southeastern South Pacific Oceans. Influences of advection and forcing are anticorrelated
along the equator and over strong currents, hinting at coupling or damping effects. Mixing is important
near sites of deep convection and mode water formation, for example, in the Labrador, Greenland,
Irminger, and Norwegian Seas. Bottom pressure at middle and high latitudes mostly reflects barotropic
processes, but baroclinic effects can be important at low latitudes.
Results demonstrate the usefulness of incorporating observations into a consistent model framework
for quantifying mechanisms of sea-level change.
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Imprints of oceanic intrinsic variability on altimetric measurements: an OGCM study. Guillaume
Sérazin, Thierry Penduff, Laurent Terray, Bernard Barnier, Jean-Marc Molines
Recent Ocean Global Circulation Model studies have highlighted the ability of the turbulent ocean to
spontaneously generate low-frequency variability of sea-level over a wide range of spatial scales
(Serazin et al., 2015). In terms of variance in the interannual band (i.e. from 1.5 to 20 years), this
intrinsic variability is very comparable to the total hindcasted variability at small scales ( 12°). This lowfrequency intrinsic variability may be seen in the 22 year record of altimetric data and we propose a
method to isolate some intrinsic features in this dataset based on a high-pass spatial filtering.
This study also focus on timescales longer than 20 years using a 300 year long 1/4° simulation, which
shows that the ocean spontaneously generates decadal sea-level fluctuations in eddy-active regions.
It is shown that this ocean-only variability may have an imprint on observed regional sea-level trend,
especially in the ACC and in the Western Boundary Current areas. The incertitude on sea-level trends
induced by truncating this decadal intrinsic variability is comparable to the one estimated from Global
Coupled Models in which the oceanic intrinsic component is not taken into account yet.
A near-uniform fluctuation dominating sea level and ocean bottom pressure variations across the
Arctic Ocean and the Nordic Seas. Ichiro Fukumori, Ou Wang, William Llovel, Ian Fenty, Gael
Forget
Across the Arctic Ocean and the Nordic Seas, a basin-wide mode of sea level and ocean bottom
pressure fluctuation is identified using satellite and in situ observations in conjunction with a global
ocean circulation model and its adjoint. The region is central to studies of sea level change because it
is where the ocean interacts with the cryosphere including Greenland’s ice sheet. The basin-wide
variation extends across the interconnected deep ocean basins of these Arctic seas with near-uniform
amplitude and phase. The fluctuation is depth-independent and dominates the region’s large-scale
variability from sub-monthly to interannual timescales. The fluctuation results from bifurcating
coastally trapped waves generated by winds along the continental slopes of the Arctic region and its
neighboring seas, including the North Atlantic Ocean. The winds drive Ekman transport between the
shallow coastal area and the deep ocean basins, creating sea level anomalies of opposite signs in the
two regions. The anomalies rapidly propagate away as barotropic coastally trapped waves that
subsequently bifurcate at the shallow straits connecting the Arctic region with the rest of the globe.
Anomalies that enter the deep Arctic basins equilibrate uniformly across the domain, isolated from
neighboring shallow variations, due to the basins’ homogeneous depth-integrated planetary potential
vorticity distribution. The study, from a technical perspective, illustrates how a thoughtful application
of the adjoint technique provides an explanation of physics that statistical analysis of model results
and/or observations cannot. Whereas correlation does not imply causation, adjoints do.
Pacific sea level trends: internally or externally forced? Felix Landerer
A prominent sea level rise pattern in the Pacific Ocean – large increases of 12 mm/yr in the West and
near-stagnant levels in the East – has been observed with satellite altimetry since the 1990s. A
significant fraction of this dipole trend pattern correlates well with the Pacific Decadal Oscillation
(PDO), a large-scale mode of internal climate variability. However, the PDO cannot fully account for
the Western Pacific Ocean trend pattern. Whether or not the remaining non-PDO pattern can be linked
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to an anthropogenic influence has been discussed in several recent studies. Here, we use a large
ensemble of CMIP5 20th century simulations (more than 150 runs from 27 different GCM setups) to
further investigate the role and contribution of the PDO and other modes of equatorial variability to
Pacific sea level change patterns. Specifically, we focus on 20-year trend patterns since 1950, and
attempt to isolate and attribute an externally forced sea level pattern by removing sea level trend
contributions from internal variability to test if the remaining patterns become more consistent across
the models, and thus support the notion of a detectable common externally forced sea level change
since 1990.
Spatial scales and the detection of externally forced signals in regional sea surface height in
CMIP5 models. Kristin Richter, Ben Marzeion
Various detection and attribution studies have found an anthropogenically forced signal in global
thermosteric sea surface height. However, detection on regional to local scales is hindered due to the
increased magnitude of internal variability on smaller spatial scales. Recent studies attempted to
quantify local internal variability to assess the time of emergence of an externally forced signal in
climate simulations. They found that, in regions of elevated internal variability such as the western
tropical Pacific Ocean, it can take several decades for a forced signal to emerge from the background
noise.
Here, we investigate the spatial scales that are necessary to detect an externally forced signal within a
selected fixed time period. Using control simulations with no evolving forcing, we quantify the
magnitude of regional internal variability depending on the degree of spatial averaging. We test various
averaging techniques such as zonal averaging, ocean basin averages and averaging gridpoints within a
selected radius. Historical and 21st-century simulations are treated the same way. By comparing the
results from control simulations with scenario simulations, the procedure allows us to estimate to what
degree the data has to be averaged spatially in order to detect a forced signal within a certain period
of e.g. 20 years (the period with available global sea surface height observations). Having identified,
for each grid point, the averaging radius that is necessary to detect an external signal during the past
20 years, the results can be applied to observations and it can be assessed on which spatial scales
regional detection and attribution studies may yield meaningful results.
Worst-case scenarios for sea level rise from ice sheet melt. Carmen Boening, Nicole Schlegel,
Michael Schodlok, Daniel Limonadi, Eric Larour, Michael M. Watkins
Uncertainties in current global mean sea level rise (SLR) estimates for the next 100 years are fairly large
and complicate decision making processes for coastal planning. Current estimates of SLR by 2100 range
between 30 cm and 2 m implying very different ramifications for planning strategies over the next
decades. The main source of uncertainty in these estimates is the future of the major ice sheets,
Greenland and Antarctica, as they hold close to 70 m of fresh water that have a large potential impact
on SLR in case of a collapse. Here, we explore upper bounds for SLR caused by ice sheet melt/collapse
by evaluating worst-case scenario runs from state-of-the-art ice sheet and ocean models of Antarctica
and the Southern Ocean. As a reference, we performed a control run, forced with a mean climatology
of surface mass balance and ice shelf basal melt rates, to assess the relative change compared to the
worst-cases; SLR from the control is ~0.2m in the next 100 years. The first worst-case we analyzed is:
the instantaneous removal of all floating ice shelves, the resulting effects on grounding line position
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and ice sheet velocities given missing backstress, and consequential SLR over the next 100 years. A
second experiment explores potential mechanisms needed to remove the ice shelves by increasing
melt rates by a factor of 100. First results indicate that both scenarios have significant impacts on SLR
over the next 100 years (remove ice shelves: 1.1 m; melt rate x 100: 2.2 m). Thus, it is important to
explore the likelihood of these scenarios. In comparison, forcing the model with maximum melt rates
from the last 20 years, which are much smaller than melt rate x 100, lead to a SLR of 0.25 m over 100
yrs, a result that is much closer to the control run and the lower limit of SLR.
Asymmetry in regional sea level rise projections due to skewed ice sheet contributions. Renske
de Winter, Thomas Reerink and Roderik van de Wal
In the latest IPCC assessment report it is assumed that the uncertainties around sea level rise (SLR)
projections are Gaussian distributed, implying that uncertainties are equally likely for both higher and
lower probabilities. However, expert judgment suggests that, as a result of ice sheet dynamics, the
contribution of ice sheet mass loss to SLR has large uncertainties towards high values. Hence, the
probability density function (PDF) of the ice sheet mass loss is skewed to higher values. In this study
we analyse how asymmetric distributions for ice sheet dynamics influence the uncertainty in regional
SLR.
The effect of skewed contributions for ice sheet dynamics are determined by combining the PDFs of
the projected contributions to SLR for Greenland, West and East Antarctica, with the PDF for regional
SLR due to climate change effects, including gravitational and rotational effects.
Near the West Antarctic and the Greenland ice sheet the new combined PDF is skewed towards
negative values due to the gravitational effect; mass loss of an ice sheet results in a sea level drop in
the vicinity of this ice sheet. For most other areas of the world, the projected PDF of SLR becomes
wider and skewed towards higher SLR values leading to increased risks of high sea level rise.
As we are mainly interested in the changes in the upper tail of the distribution, we analyse our results
by comparing the difference in mean with difference of the upper 95, 97 and 99% interval. Averaged
over the ocean the additional increase in sea level rise are 0.19, 0.22 and 0.28 m for the different
intervals. Locally, with the east coast of the US as an example, the increase in the tail amounts up to
0.24, 0.28 and 0.36 m for respectively the 95%, 97% and 99% intervals.
Posters
Analysis of the regional pattern of sea level change due to ocean dynamics and density change
for 1993–2099 in observations and CMIP5 AOGCMs. Roberto A. F. Bilbao, Jonathan M. Gregory,
Nathaelle Bouttes
Predictions of twenty-first century sea level change show strong regional variation. Regional sea level
change observed by satellite altimetry since 1993 is also not spatially homogenous. By comparison
with historical and pre-industrial control simulations using the atmosphere–ocean general circulation
models (AOGCMs) of the CMIP5 project, we conclude that the observed pattern is generally dominated
by unforced (internal generated) variability, although some regions, especially in the Southern Ocean,
may already show an externally forced response. Simulated unforced variability cannot explain the
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observed trends in the tropical Pacific, but we suggest that this is due to inadequate simulation of
variability by CMIP5 AOGCMs, rather than evidence of anthropogenic change. We apply the method
of pattern scaling to projections of sea level change and show that it gives accurate estimates of future
local sea level change in response to anthropogenic forcing as simulated by the AOGCMs under RCP
scenarios, implying that the pattern will remain stable in future decades. We note, however, that use
of a single integration to evaluate the performance of the pattern-scaling method tends to exaggerate
its accuracy. We find that ocean volume mean temperature is generally a better predictor than global
mean surface temperature of the magnitude of sea level change, and that the pattern is very similar
under the different RCPs for a given model. We determine that the forced signal will be detectable
above the noise of unforced internal variability within the next decade globally and may already be
detectable in the tropical Atlantic.
Global reconstructed daily storm surge levels from the 20th century reanalysis (1871-2010). Alba
Cid, Paula Camus, Sonia Castanedo, Fernando Méndez, Raúl Medina
The study of global patterns of wind and pressure gradients, and more specifically, their effect on the
sea level variation (storm surge), is a key issue in the understanding of recent climate changes. The
local effect of storm surges on coastal areas (zones particularly vulnerable to climate variability and
changes in sea level), is also of great interest in, for instance, flooding risk assessment.
Studying the spatial and temporal variability of storm surges from observations is a difficult task to
accomplish since observations are not homogeneous in time and scarce in space, and moreover, their
temporal coverage is limited. The development of a global storm surge database (DAC, Dynamic
Atmospheric Correction by Aviso, Carrère and Lyard, 2003) fulfils the lack of data in terms of spatial
coverage, but not regarding time extent, since it only includes last two decades (1992-2014).
In this work, we propose the use of the 20CR ensemble (Compo et al., 2011) which spans from 1871 to
2010 to statistically reconstruct storm surge at a global scale and for a long time period. Therefore, the
temporal and spatial variability of storm surges can be fully studied and with much less effort than
performing a dynamical downscaling.
The statistical method chosen to carry out the reconstruction is based on multiple linear regression
between an atmospheric predictor and the storm surge level at daily scale (Camus et al., 2014). The
linear regression model is calibrated and validated using daily mean sea level pressure fields (and
gradients) from the ERA-interim reanalysis and daily maxima surges from DAC.
Hence, this work provides a daily database of maximum surges that can be used for the scientific
community to improve the knowledge on historical storm-surge conditions.
Nonlinear model of the long-term sea-level fluctuations in the Caspian Sea. Anatoly V. Frolov
Long-term sea-level fluctuations in the Caspian Sea (CSL) are considered as the output process of the
essentially nonlinear system with negative and positive feedback. The elaborated model is based on
the analysis of CSL fluctuations and water balance data for 1880-2013. The model also takes into
account the water outflow from the Caspian Sea into Garabogazköl Bay, which is the function of CSL.
According to the model, the probability density function (PDF) of the CSL is derived as the solution of
the Fokker-Planck-Kolmogorov equation. We used this model to examine the influence of the
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mathematical expectation of inflow on the CSL PDF. It is shown that the bilinear properties of the CSL
PDF can exist only for a certain range of mean inflows. Some applied aspects of the CSL modeling are
also discussed.
Sea Level Complexity in Observations And Models. M. Karpytchev, M. Becker, M. Marcos, S.
Jevrejeva, S. Lennartz-Sassinek
Most tide gauge records can be represented as outcomes of stochastic power-law process with a Hurst
exponent 0.5 indicating the presence of long-term time correlations. The long-term correlated records
manifest a specific long-term persistence behavior: large events well above the average are more likely
to be followed by large events, and small events by small events. The spatial variations in the
magnitude of the Hurst exponent in the observed sea level records seem to follow regular patterns
that is
potentially important for understanding sea level changes and for developing an adequate noise
model required by an accurate sea level trend estimation. We compare the spatial distribution of the
Hurst exponents derived from the observations with those predicted by the global climate models and
discuss the possible links between the scaling and the main features of the global ocean-atmosphere
circulation.
Explaining the spread of CMIP5 climate models in global-mean thermosteric sea level rise over
the 20th and 21st centuries. B. Meyssignac, A. Melet
The ocean stores more than 90% of the energy excess associated with anthropogenic climate warming.
The resulting warming and thermal expansion of the ocean is a leading contributor to sea level rise.
Confidence in projections of global mean sea level rise therefore depends on the ability of climate
models to reproduce ocean warming and induced global mean thermosteric sea level (GMTSL) over
the 20th century. This study aims at explaining and trying to reduce the spread of GMTSL across climate
models of the Coupled Models Intercomparison Project Phase 5 (CMIP5) over the 20th and 21st
centuries.
We first show that the GMTSL rise computed from climate models is approximately proportional to
the radiative forcing. The constant of proportionality mostly depends on the climate feedback
parameter and the ocean heat uptake efficiency. From that linear relationship, we show that the
spread in the net top-of-atmosphere radiative flux (N) explains most of the spread in projections of the
GMTSL. The inter-model spread of N is itself mostly explained by the spread in the radiative forcing
changes while the spread in climate feedback parameter and ocean heat uptake efficiency play a
smaller role.
We then compare GMTSL from climate models to observational estimates over the 1961-2005 period.
Although the model-ensemble mean is within the uncertainty of observations, a significant number of
models consistently overestimate or underestimate the observed GMTSL rise. The contribution of the
deep ocean (below 700 m depth) to GMTSL is largely spread among climate models (33+/-28% over
1900-2005). Selecting the sub-ensemble of models that conserve the energy in the climate system and
are within the observational estimates of GMTSL reduces that spread and leads to a contribution of
35+/-10%.
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The uncertainty in projected GMTSL in 2100 can also be reduced with a selection of climate models
based on the comparison of the climate feedback parameters, ocean heat uptake efficiencies and 20th
century radiative forcings of the sub-ensemble of climate models that best reproduce the observed
GMTSL over 1961-2005.
Multi-annual predictability of regional sea level in a global climate model. C. D. Roberts, N.
Dunstone. L. Hermanson, M. Palmer, D. Smith
Recent work has demonstrated that some aspects of regional sea level are predictable on seasonal
time scales using a global climate model initialized with an appropriate ocean state (Miles et al. 2014).
However, the predictability of regional sea level on multi-annual time-scales has yet to be evaluated.
Here, we present an initial assessment of the predictability in time-mean dynamic sea level using fiveyear hindcasts from the latest configuration of the UK Met Office Decadal Prediction System
(DePreSys3), a coupled ocean-atmosphere-sea ice model with an eddy-permitting ocean resolution.
Hindcasts are initialized from a model assimilation of a full-depth ocean analysis and skill is evaluated
against satellite altimetry and tide-gauge reconstructions of sea surface height.
Miles et al. "Seasonal prediction of global sea level anomalies using an ocean–atmosphere dynamical
model." Climate Dynamics 43.7-8 (2014): 2131-2145.
Statistical modeling of Sea Level for regional semi-enclosed basins. Luca Scarascia and Piero
Lionello
This study analyzes the deviations of semi-enclosed regional basins from the global mean sea level (SL).
It considers three cases: the Baltic, Adriatic and Black Sea. The aim is to develop a statistical model for
estimating to which extent the SL of these basins will depart from the mean global level in the future.
The past SL of these three basins can be estimated from tide gauge records that are available in the
PSMSL database (13, 7, 4 tide gauges in the Baltic Sea, Adriatic Sea and Black Sea, respectively). SL data
are considered after the subtraction of the Inverse Barometer (IB) effect. By a statistical method, based
on PCA and Least Squares Method (LSM), a continuous time series Baltic and Adriatic Sea level from
1901 to 2009 has been obtained. Lack of data (in the first part of 20th century and in the last decade
before 2009) and substantial disagreement in several parts of the records prevent obtaining the
analogously continuous results for the Black Sea. A multivariate linear regression model is used to
investigate the link between SL anomaly, computed as the difference between the regional SL and
global SL, and three large scale climate variables (sea level pressure, air temperature and
precipitation). Mean sea level pressure is found to be the main factor reproducing the past SL
variability. The linear model at a monthly scale provides a quite good reconstruction of the past
variability for Baltic and Adriatic Sea, but with substantial differences in the reconstruction skill
between cold and warm seasons. The skill of the model is substantially worse for Black Sea than for
the two other basins. The same linear model forced by CMIP5 model simulations is used for SL
projections until 2100.
This study is part of the activities of RISES-AM project (FP7-EU-603396).
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Projections of 21st Century Sea Level Changes for Norway. Matthew J. R. Simpson, J. Even Ø.
Nilsen, Oda Ravndal, Kristian Breili, Halfdan P. Kierulf, Holger Steffen, Eystein Jansen, Hilde Sande,
Mark Carson
For effective coastal management it is important to understand how sea levels will change locally in
the future. Changes to mean sea level and sea level extremes (e.g., storm surges) will lead to changes
in coastal impacts. Preparedness is normally based on return levels from statistics of the water levels
in the observed record. With changing mean sea levels due to climatic change and land uplift return
levels will change accordingly. The goal of this work is to provide projections of future return levels for
each coastal municipality in Norway.
We first perform an extensive and comparative analysis of observed sea level from tide gauges and
altimetry, in order to assess the current rates and natural variability. State of the art land uplift rates
for the coastal municipalities are determined assessing new GPS observations as well as GIA modelling.
Our regional sea level projections are based on findings from the Fifth Assessment Report (AR5) of the
Intergovernmental Panel for Climate Change (IPCC), and the Coupled Model Intercomparison Project
phase 5 (CMIP5) output, but using our own land uplift rates and corresponding gravitational effects on
sea level, as well as estimates of self attraction and loading. The average projected 21st century relative
sea level change in Norway is -0.10–0.35 m (90% uncertainty bounds) for RCP2.6, 0.00–0.45 m for
RCP4.5, and 0.10–0.65 m for RCP8.5. However, the relative sea level projections can differ as much as
0.50 m from place to place, mostly governed by the land uplift pattern.
Further, the extreme value analysis and return levels for Norway have been reassessed, and together
with the sea level projections applied to a modified version of Hunter’s method. We thus provide
estimates for how much assets need to be raised so that the probability of flooding remains preserved.
Sea surface height variability in the North East Atlantic from satellite altimetry. Paul Sterlini, Hylke
de Vries and Caroline Katsman
Sea surface height variability (SSV) operates in varying temporal and spatial scales and acts as a source
of noise when trying to perform long term trend analysis on the sea surface height (SSH). This study
seeks to identify (and ultimately remove) the major contributing components of the SSV in the NorthEast Atlantic to expose the underlying changes in the SSH signal. This allows a trend analysis on the
"cleaned" SSH for an accurate determination of sea level rise.
Observations of sea level anomalies are taken from 21 years of satellite altimeter data and are used to
estimate the SSV in the North-East Atlantic. Seasonal signals are removed and monthly means
calculated. The SSV is decomposed into global, regional and local components and a simple multiple
linear regression model is constructed on the basis of these components to model the explained SSV.
Initial results show that a region of high SSV exists off the west coast of Denmark and can be well
represented with a regression model which uses local wind and global temperature as primary
regressors. This work will help in understanding regional sea level change over the past 21 years and
to provide a foundation for estimates of local sea level change in the near future.
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What is the most robust time series analysis tool to isolate mean sea level from tide gauge
records?. Phil Watson
One of the most critical environmental issues confronting mankind into the foreseeable future remains
the ominous spectre of climate change, in particular the pace at which impacts will occur and our
capacity to adapt. Sea level rise is one of the key artefacts of climate change that will have profound
impacts on global coastal populations. Although extensive research has been undertaken into this
issue, there remains considerable conjecture and scientific debate about the temporal changes in
mean sea level and the climatic and associated physical forcings responsible for them. In particular,
over recent years, significant debate has centred around the issue of a measurable acceleration in
mean sea level, a feature central to projections based on the current knowledge of climate science.
The complexity of the dynamic influences and noise embedded within ocean water level data sets has
led sea level research toward successively more sophisticated time series techniques to estimate the
trend. In the absence of an absolute knowledge of the mean sea level signal (or trend) for a particular
record, the accuracy of the trend has increasingly been inferred from the assumed sophistication of
the applied analytic. An innovative and transparent process by which to identify the most efficient
technique for isolating the mean sea level signal is to test such approaches against “synthetic” (or
custom built) data sets with a known mean sea level signal. This paper details the development of a
comprehensive monthly average data set comprising 20,000 time series to meet the above-mentioned
objective. The paper also presents the results of the detailed testing using an extensive array of time
series techniques to reveal the most statistically robust analytic for isolating mean sea level from
conventional ocean water level records with improved temporal resolution.
Regional evaluation of surface mass balance forcing of an ice flow model for the Greenland Ice
Sheet using GRACE mascon solutions. D. N. Wiese, N.-J. Schlegel, M. M. Watkins, E. Y. Larour, J.
E. Box, X. Fettweis, M. R. van den Broeke
Quantifying Greenland's future contribution to sea level rise is a challenging task and requires accurate
estimates of ice flow sensitivity to changing climates. Transient ice flow models are promising tools
for estimating future ice sheet behavior; however, confidence in these types of projections is low due
to a scarcity of data for validation of model historical runs. For more than a decade, the Gravity
Recovery and Climate Experiment (GRACE) has continuously acquired time-variable measurements of
the Earth's gravity field and has provided unprecedented surveillance of mass balance of the ice sheets,
offering an opportunity for ice sheet model evaluation. Here, we take advantage of a new highresolution (~300 km) monthly mascon solution for the purpose of mass balance comparison with an
independent, historical ice flow model simulation using the Ice Sheet System Model (ISSM). The
comparison highlights which regions of the ice sheet model differ most from GRACE observations.
Investigation of regional differences in trends and seasonal amplitudes between simulations forced
with different Regional Climate Model (RCM)-based estimates of surface mass balance (SMB) allows
us to make conclusions about the relative contributions of errors in both models of SMB and ice
dynamics. We highlight the importance of utilizing an ice flow model for future projections rather than
relying solely on projecting future changes in SMB. This study constitutes the first regional comparison
of GRACE data and an ice sheet model. Conclusions will aid in the improvement of RCM SMB estimates
as well as ice sheet simulation estimates of present and future rates of sea level rise.
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Sea Level Extremes
Oral Presentations
Nineteenth Century Sea-level and Extremes on the US East and West Coast. Stefan Talke, David
Jay, Patrick Lau, Conrad Hilley, Lumas Helaire, Drew Mahedy, Ramin Familkhalili
Continuous tidal measurements began in 1844 and 1853 on the East and West coast of the United
States, but only a small portion of these data have been analyzed for sea-level rise and extreme events.
In this presentation we describe the progress of efforts to recover and digitize more than 200 stationyears of 19th and early 20th century data from Boston (MA), Sandy Hook (NJ), Charleston (SC), Norfolk
(VA), Wilmington (SC), San Diego (CA), Astoria (OR), Port Townsend (WA), Sitka (AK) and Kodiak (AK).
Over 50,000 pictures have been taken at the US National Archives and local archives, and more than 1
million data points digitized by students. Approximately 15 years of tide-charts (marigrams) from
Astoria, OR (1853-1876) have been digitized at 1 minute resolution using a software-based line
recognition program we developed. Traditional harmonic analysis, spectral analysis, and waveletbased tidal analysis are used to quality assure data and identify periods of anomalous (bad) data. The
role of hydrodynamic gradients on sea-level collected at different station locations will be assessed,
and the challenges of connecting historical sea-level to a modern datum in tectonically active regions
will be discussed. Preliminary results suggest that the 19th century data is valuable for assessing longterm trends in sea-level, sea-level acceleration, and extremes. Results suggest that the once-in-10
year storm tide in New York City has increased by nearly 0.3m since the 1850s. Preliminary results also
suggest that tidal range in Wilmington (NC) has doubled since 1887, leading to a more than 1m increase
in the worst-case scenario storm surge (a category 5 hurricane). Hence, 19th century data provide
insights into trends in the total water spectrum and can help local efforts to adapt to climate change.
Storm surge clustering and spatial footprints: How extreme was the 2013-2014 UK storm surge
season? Ivan D. Haigh, Matthew P. Wadey, Shari L. Gallop, Robert J. Nicholls
Coastal flooding can be devastating, with long-lasting and diverse consequences. The UK has a long
history of severe coastal flooding. The continued threat of serious flooding was apparent during winter
2013–2014 when the UK experienced a series of storm surge events. What is noteworthy about the
2013-14 winter period is the: (1) large number of exceptional high waters and coastal floods over a
relatively short time period; and (2) the large number of coastal regions affected. Extreme events are
rarely assessed in terms of temporal ‘clustering’, despite the fact that ‘repeated shocks’ to defences
and communities can reduce time for recovery and lead to amplified flood damages. The spatial
dependence or ‘footprint’ of flood hazards is also receiving more attention, motivated by concern from
re-insurance, infrastructure reliability and emergency response.
Here we assess how unusual the 2013-14 storm surge season was in the last 100 years, in terms of
both temporal ‘clustering’, and the spatial ‘footprint’ of events. To do this we analyse sea level records
at the UK’s national tide gauge sites, and use a threshold of the 1 in 5 year return period to select high
waters that are potentially relevant to flooding. Using meteorological re-analysis data, we determine
storms tracks and characteristics that generated these extreme sea level events. In total, we identify
96 events that generated water levels greater than the (1 in 5 year return period) threshold. For each
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event, the time to the next nearest event is calculated and the spatial footprint estimated. This is
compared for all years on record. Finally, we consider how to improve estimates of extreme sea levels
using advanced statistical methods that can represent event clustering and footprints; in order to
provide stakeholders with tools to improve how coastal flood risk is identified, assessed and planned
for.
Regional climate variability in extreme sea levels from satellite altimetry observations over two
decades. Melisa Menendez, Philip L. Woodworth
The patterns of variability and change in extreme sea levels are of particular interest for both scientific
and practical reasons. Observations from tide gauge records are the main source of sea level
information at the coast, however, for deep ocean and some coastal areas no or only very short and
incomplete measurements exit.
Sea surface height from satellite altimetry provide sea level variability info over the last two decades.
This study analyzed a inter-calibrated satellite altimetry data set of Topex/Poseidon, Jason and
OSTM/Jason2 missions from 1993 to 2012.
A global analysis if extreme sea level is made by aggregating individual measurements into grid boxes
with approximately two values per day. The parameters of the Generalised Extreme Value Distribution
describes the behavior of the most unusual extreme events. Location and scale parameters presents
the types of variability associated primarily with fluctuations in the ocean circulation. Positive shape
parameter values include the eastern tropical Pacific, northern extratropical coastal areas in the
western Pacific and Atlantic Oceans, a band across the Aleutian Islands and at high latitudes.
The seasonal fluctuations, interannual variability and trends are also investigated by using a timedependent extreme model. The influence of the Arctic Oscillation (AO), North Atlantic Oscillation
(NAO), El Niño south oscillation (Niño 3 index), and Southern Annular Mode (SAM) on extreme sea
levels is assessed by introducing the climate indices as covariates into the model. Finally, regional
positive linear trends in extreme sea levels are determined largely by the corresponding spatial
variations in mean sea level changes worldwide.
Time varying trends in sea level extremes. Marta Marcos, Francisco M. Calafat, Angel Berihuete,
Sönke Dangendorf
While there is scientific consensus on mean sea level rise during the last century at both global and
regional scales, changes in extreme sea levels are more uncertain. Accurate assessments of the
likelihood of extreme events are essential to i) describe the temporal variability in extreme frequency
and intensity and quantify its probability of occurrence, ii) understand the processes that drive
extreme sea level events and iii) plan and adopt strategies for coastal management. Here we use state
space models to evaluate non-stationary changes in extreme sea levels and derive time-varying return
periods. We have used a set of long (>50 years) coastal tide gauges with hourly sampling worldwide
distributed and we seek for regional and temporal consistency in the observed changes in sea level
extremes
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Cyclone Xaver seen by Geodetic Observations. Leonor Mendoza, Luciana Fenoglio-Marc, Remko
Scharroo, Alessandro Annunziato, Matthias Becker, John Lillibridge
Cyclone Xaver pounded the North Sea on 5-6 December 2013 and reached its maximum in the German
Bight the second day. The radar altimeter on-board the SARAL/AltiKa satellite measured the largest
storm surge signal captured by satellite altimetry to date, nearly 3 m, at the maximum. A local dense
network of in-situ stations (tide gauges and GPS) monitored the event over several days. The combined
geodetic measurements detect alongshore and cross-shelf surge variations and land subsidence.
The GPS network detects a maximum land subsidence at the GPS locations of 4-6 cm, in excellent
agreement with the loading of the predicted surge by two forecast models in both measure and
occurrence. The differences between the surge model predictions at the peak event are mainly caused
by different wind forcing and reduce from 1 to 0.3 meters when the same wind forcing is used in both
models.
Observations largely agree with model predictions on wind speed (Root-Mean-Square (RMS) of the
differences is 4 m/s) and surge height (RMS 30 cm) and mostly differ on wave height (RMS 2 m).
The temporal and spatial characteristics of the surge and vertical displacement derived from the
observations along the coast agree with the simulations. The water height indicates both a direct large
scale forcing and a shelf wave dynamics with anticlockwise propagation of the surge. Instead, the
temporal and spatial evolution of the vertical displacement appears to be mainly affected by this last
component. After post-processing, the 1-minute sampling GPS time series monitor very well the
propagation direction of the storm; the maximum subsidence is reached in the stations following the
anticlockwise path of the surge. The along-track off-shore observations provided by satellite altimetry
are valuable information to validate the simulations off-shore.
The results underline the importance of geodetic measurements in improving existing forecast
approaches.
Future storm surge levels - the example of Denmark. Kristine S. Madsen, Torben Schmith, Tian
Tian
Sea level rise will be one of the dominating effects of global warming, and one of the main impacts will
be on storm surges. Here we assess the changing wind contribution on future storm surges in the North
Sea – Baltic Sea region and combine it with mean sea level rise projections from the latest IPCC report
and from regional studies, in preparation for dedicated hydrodynamic simulations including both. We
will discuss the impact of land rise and changing tides. The changes in extreme sea level due to wind
has been assessed by dynamically downscaling GCM results using a regional atmospheric climate
model and the same hydrodynamic ocean model as is used for operational storm surge modelling in
Denmark. The assessment shows possibilities for increased storm surge contributions of up to 0.3 m
on exposed coasts of the North Sea and the Baltic Sea, whereas no significant changes are seen along
more sheltered coastlines. This increase must be combined with changes of the mean sea level. The
observed sea level rise in Denmark, when corrected for land rise, lies very close to the global mean
value of the last century. For the future, the IPCC AR5 projections of mean sea level rise of the North
Sea - Baltic Sea area from 1986-2005 to 2081-2100 range from 0.3 m to 0.6 m for the four RCPs, with
and standard deviation of approximately 0.3 m. The IPCC report does not give an upper range for risk
assessments, but DMI has, in corporation with University of Copenhagen, estimated and upper limit
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for a medium-high climate scenario for Denmark to be 1.4 m by year 2100. Today, a storm surge of 1.5
m is a 100-year event in Copenhagen. With a sea level rise of 0.5 cm, this level will be reached every
second year.
Meteorological Tsunamis In The World Oceans: An Overview. Alexander Rabinovich
“Meteorological tsunamis” (or “meteotsunamis”) are destructive tsunami-like waves that have
approximately the same temporal and spatial scales as ordinary tsunami waves and can affect coastal
areas of the ocean in a similar devastating way. In particular regions and in certain situations,
meteotsunamis can have catastrophic effects and even lead to death. Meteotsunamis are generated
by various types of atmospheric disturbances, including trains of atmospheric gravity waves, passing
fronts, squall lines, and jumps in atmospheric pressure.It is common for strong meteotsunamis to be
associated not with some extreme events, like typhoons and and hurricanes, but with calm weather
associated with high-pressure systems. There are some specific regions where meteotsunamis are
regularly observed: the Balearic Islands, Spain; west coasts of Sicily, Italy and the Adriatic Sea, Croatia;
Kyushu Island, Japan; Longkou Harbour, China, and the Great Lakes, USA-Canada. Meteotsunamis have
a resonant mechanism of generation and cited particular regions have favourable conditions for their
formation. However, considerable interest in the tsunami problem, in general, initiated by the
catastrophic 2004 Sumatra and 2011 Tohoku tsunamis, and by significant improvement in
instrumentation (high-precision tide gauges and microbarographs) recording these events, has
recently led to new information on meteorological tsunamis and demonstrated that this is a much
more common and widespread phenomenon than had been considered previously. Major
meteotsunamis in 2013-2014 occurred on the East Coast of the USA, in Brazil, in the Gulf of Mexico, in
Australia and the Mediterranean. All of these events were well documented and are under thorough
investigation. The key scientific and applied question is the elaboration of effective and reliable
methods of meteotsunami forecasting.
The impact of sea level rise on storm surge water levels and wind waves. Arne Arns, Jürgen Jensen
The impact of sea level rise on extreme water levels and wind waves is investigated using a numerical
model that covers the entire North Sea, but has its highest spatial resolution in the northern part of
the German Bight. A 40-year hindcast covering the period 1970 to 2009 is conducted using observed
mean sea level changes, tides and atmospheric forcing as boundary conditions. The model reproduces
the observed water levels and wind waves well for this control period. A second 40-year run is then
conducted considering the same atmospheric forcing but adding +0.54 m to the MSL to explore the
effects of sea level rise on storm surges and wind waves in the investigation area.
At most locations, the second model run leads to changes in the storm surge water levels that are
significantly different from the changes in MSL alone. The largest increases of the order of 15 cm (in
addition to the MSL changes) occur in the shallow water areas of the Wadden Sea. These increases are
caused by nonlinear changes in the tidal constituents which, however, are spatially not coherent. Also
the wave heights show significant increases which are mainly caused by the larger water depth
reducing the association between storm surge water levels and depth limited wave heights.
Finally, we estimate the impact of SLR on return water levels using extreme value analyses. Our
analyses highlight that this impact is nonlinear and spatially incoherent. In some locations, the increase
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in return water levels is nearly constant for all exceedance probabilities with values exceeding the
considered SLR by 7-10 cm. Together with the simulated changes in wind waves, required increases in
design levels (considering water levels and wind waves or wave run-up) are expected to be
considerably above the rate of SLR alone. For instance, to keep the current safety levels, coastal
defenses need to be improved by up to twice the considered SLR locally.
Atmospheric Circulation Changes and their Impact on Extreme Sea Levels and Coastal Currents
in Australia. Kathleen L. McInnes, Frank Colberg, Julian O’Grady
Extreme sea levels are a significant hazard for many low-lying coastal communities, causing a range of
coastal impacts such as flooding and erosion. Changes in atmospheric circulation patterns and severe
weather systems may therefore lead to changes in the frequency and intensity of extreme sea levels
and the strength of coastal currents. In this study a hydrodynamic model at 5 km resolution has been
implemented over Australia to investigate future changes to sea levels and currents. The role of tidesurge interaction is first assessed and found to have negligible effects on storm surge heights over
most of the coastline. Tidal forcing is therefore omitted in the climate change simulations. Twentyyear simulations are carried out over the time periods 1981-1999 and 2081-2099 using atmospheric
forcing from four CMIP5 climate models. Results suggest that extreme sea levels will undergo small
changes along much of the Australian coastline. However there are some regions along the north and
south coasts of mainland Australia that appear to be sensitive to projected changes in circulation
patterns, particularly in the Austral summer months. These changes and their possible coastal impacts
will be presented and discussed.
Global Secular Changes in different Tidal High Water, Low Water and Range levels. Robert J.
Mawdsley, Ivan D. Haigh,N.C. Wells
Tides exert a major control on the coastal zone by influencing high sea levels and coastal flooding,
navigation, sediment dynamics and ecology. Therefore, any changes to tides have wide ranging and
important implications. In this paper, we uniquely assess secular changes in 15 regularly used tidal
levels (five high water, five low water and five tidal ranges), which have direct practical applications.
Using sea level data from 220 tide gauge sites, we found changes have occurred in all analysed tidal
levels in many parts of the world. For the tidal levels assessed, between 36% and 63% of sites had
trends significantly different (at 95% confidence level) from zero. At certain locations, the magnitude
of the trends in tidal levels were similar to trends in mean sea level over the last century, with observed
changes in tidal range and high water levels of over 5mm/yr and 2mm/yr respectively. More positive
than negative trends were observed in tidal ranges and high water levels, and vice versa for low water
levels. However we found no significant correlation between trends in mean sea level and any tidal
levels. Spatially coherent trends were observed in some regions, including the north-east Pacific,
German Bight and Australasia, and we also found that differences in trends occur between different
tidal levels. This implies that analysing different tidal levels is important. Because changes in the tide
are widespread and of similar magnitude to mean sea level rise at a number sites, changes in tides
should be considered in coastal risk assessments.
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Posters
How to interpret expert judgment assessments of 21st century sea-level rise? Hylke de Vries,
Roderik S.W. van de Wal
Over the last years it has been realized that the ice dynamical contribution of ice sheet to sea level can
possibly not be estimated in a deterministic way. As a result a few expert assessments have attempted
to estimate sea-level rise. It turned out that experts have a strongly diverging opinion on the ice sheet
contribution. We argue that such lack of consensus should form an essential and integral part of the
subsequent analysis of the data. By employing a method that keeps the level of consensus included,
and that is also more robust to outliers and less dependent on the choice of the underlying
distributions, we obtain on the basis of the same data lower high-end estimates. We show that results
are sensitive to assumptions on the shape and minimum of the underlying distributions. Our analysis
therefore demonstrates that one should be careful in considering high-end sea-level rise estimates as
being well-determined and fixed numbers.
Long-term changes in sea level extremes and tides on the Chinese coasts. Xiangbo Feng, M. N.
Tsimplis and P.L. Woodworth
Sea level records from 1954 to 2012 at twenty tide gauges at and adjacent to the Chinese coasts are
used to analyse changes in sea level extremes and tides. Significant increase in sea level extremes is
primarily driven by changes in median sea level, but also linked with increases in tidal amplitudes at
some stations. Tropical cyclones, median sea level and the 18.6-year nodal cycle are found to have
different impact on inter-annual variations of the extremes in different regions. The climate indices
are attempted to link with sea level extremes. An interesting finding is that global mean atmospheric
temperature appears to be a good descriptor of the interannual variability of tidal residual extremes
induced by tropical cyclones but the trend in global temperature is inconsistent with the lack of trend
in the residuals.
The tidal changes are also highlighted. The semidiurnal tidal parameters show significant secular trends
in the Bohai and Yellow Seas, on the north coast, and in the Taiwan Strait. The largest increase is found
for M2 for which the amplitude increases by 4-7 mm/yr in the Yellow Sea. Apart from linear trends,
the 18.61-year nodal and 8.85-year perigean cycles are also resolved in the main constituents.
Observed nodal modulations of O1 and K1 are in agreement with the equilibrium tidal theory, except
in the South China Sea. However, the observed modulations of the M2 and N2 amplitudes are smaller
than theoretically predicted at the northern stations and larger at the southern stations.
Expected Vertical Load in coastal GPS due to a Tsunami like the 1775 Lisbon Tsunami: GPS
Tsunami Early-Warning capabilities. Leonor Mendoza
An approach for tsunami early warning is studied, based on GPS observations of the vertical crustal
loading caused by a tsunami-induced redistribution of water.
The test area is the Atlantic coast of the Iberian Peninsula. Due to the lack of real tsunami recordings
in the region, this approach could not be tested using data recorded in-situ. Instead, the GPS sensitivity
and detection capability has been evaluated for coastal stations in the Iberian Peninsula during two
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periods of extremely high tides in 2011. GPS measurements have been compared to vertical
displacement caused by the predicted and observed water levels. GPS data corrected for the predicted
ocean tidal loading does not show any signal above noise level in those periods.
Moreover, two tsunami models (best- and worst-case scenarios) have been used to estimate the
crustal vertical deformation due to a tsunami with similar characteristics of the 1755 Lisbon tsunami.
Arrival times of the maximum subsidence and water height have been compared in order to establish
the possible warning time available for each scenario. This accommodation time is fundamental for
the early warning of an incoming tsunami, because the subsidence experienced and the amount of
water traveling toward the coast are intrinsically linked.
Analysis of recent high-frequency sea level events in the European Atlantic coast: impact on the
design of automatic algorithms for tsunami detection. Begoña Pérez Gómez, Marta Gómez Lahoz,
Enrique Álvarez Fanjul, Carlos González, François Schindele
The upgrade of the sea level networks worldwide, to allow their integration in the sea level related
hazards warning systems, have increased significantly our possibilities of measuring and analysing high
frequency sea level oscillations. Many tide gauges around the European waters provide today 1’ (or
less) sea level data which reveal the common occurrence of such events, with periods of several
minutes. Their origin and spatial distribution is diverse and must be better understood, for a correct
design and interpretation of the automatic detection algorithms to be used by the tsunami warning
centers in the region. We will present here the analysis of two events recorded in the European Atlantic
coast: the wave induced “seiches” occurred along the North of Spain during the storms of January and
February of 2014, and the potential detection of a small tsunami after an earthquake in the midle of
the Atlantic the 13th of February of 2015. The former caused significant floods in towns and villages
and an stunning increase of the waves induced coastal damage that was present in the media during
weeks. The second, however, was just a small signal present in several tide gauges in the Atlantic coast
that, although fortunately unnoticed by the local population, could yield significant information for
tsunami wave modellers and the development of tsunami detection software. In both cases the
REDMAR tide gauges from Puertos del Estado did send automatic messages to the network operators,
that revealed the importance and relatively well performance of the automatic detection algorithms
developed for this network. This study will provide, therefore, not only the physical description of the
two mentioned events but, at the same time, a better understanding of the limitations of this type of
automatic algorithms and the possible improvements on the information provided to the tsunami
warning centers in order to distinguish clearly both types of signals.
Estimation extreme sea levels from the combination of tides and storm surges for the coasts of
the Sea of Okhotsk. Georgy Shevchenko
Extreme sea levels arising from the combination of tides, seasonal and meteorologically-induced
oscillations (including the extreme events, storm surges) were estimated by the joint probability
method for the coast of the Sea of Okhotsk and the Pacific coast of the Kuril Islands. The sea level
observations at 10 coastal tide gauges (6 stations on the Kuril Islands, 3 on the eastern coast of Sakhalin
Island and 1 on the northern coast of the Sea of Okhotsk) were examined. High quality 1-year time
series of hourly sea level data were used for harmonic tidal analysis. The tidal heights at most stations
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are about 1.5 - 2 m, and only at Magadan they are much larger (about 5 m). Storm surges have the
largest heights for the central Kuril Islands (Matua and Iturup islands), while at the North and South
Kuril Islands the surge heights are the smallest. The winter maximum in sea level is a specific feature
of seasonal variations in this region which is associated with the winter amplification of cyclonic
circulation over the Sea of Okhotsk and with the prevailing winds. The monthly mean sea level series
were used to compute the amplitudes and phases of annual (Sa) and semiannual (Ssa) seasonal
constituents. The mean values of seasonal harmonics were used to calculate the probability density
functions (PDF) in combination with tides. Predicted time series for the 19-years interval (we used
2000-2018 to take into account the 18.6 years tidal nodal cycle) were used to calculate the PDF
(histogram) with class interval 5 cm. The residual series (after subtracting tides and seasonal variations)
were used to analyze meteorologically-induced sea levels and storm surges, and to calculate their PDF
(histogram of total residual series). Storm surges have the largest heights for the central Kuril Islands
(Matua and Iturup) islands.
Spatial variation in extreme water levels in the Baltic Sea – North Sea transition from tide gauge
records. Carlo Sørensen, Ole B. Andersen, Per Knudsen
Extreme water levels in the Baltic Sea – North Sea transition are governed by a variety of factors (met
forcing, nearshore bathymetry and profile slopes, coastline orientation, water compartment
configuration, fiord sills etc) that provide a complex picture between locations. Currently about 70 tide
gauges (TG), with data series ranging from less than 20 to 125 years (21 TG 60y), are deployed along
the 7,300 long and diverse Danish coastline (in addition to these are Swedish, Norwegian and German
TGs). Unfortunately, many of the long data series have not been digitized (pre-1970s) and where only
the extremes have been extracted in the past. Some full series are available e.g. for digitization,
whereas others are deemed to have been lost. Furthermore, data quality is varying. Still, in toto, TGs
provide a unique background data set for EVA on water levels. In an on-going study, we research the
spatial variation and regionalization in order to provide more objective and robust statistics. This
includes among other detrending, choice of distribution functions (building on the work of Arns et al,
2013), and possible ways of including historical events of an assumed very low probability. The paper
outlines the methodological approach, presents results from selected water compartments and the
work ahead, as well as some core issues of validation of TG series and statistics (not often addressed;
e.g. temporal coherence and TG’s ability to actually measure the “true” extremes) are highlighted to
discuss these matters with the scientific community at the workshop.
The Impact of an Eroding Barrier Island on Extreme Water Levels in the Tampa Bay Area. Marius
Ulm, Arne Arns, Jürgen Jensen
Barrier islands characterize an eighth of the global coastlines. Since barrier islands are part of a dynamic
coastal regime, a change in their shape or even a complete erosion may lead to an increased impact
of storm surge events on the mainland. A barrier island which is under the particular threat of erosion
is Egmont Key, located in the mouth of the Tampa Bay estuary in Florida.
For the investigation of the influence of barrier islands on storm surge water levels at the mainland’s
coast, two 2D depth averaged hydrodynamic-numerical models of the Gulf of Mexico and of the
adjacent Tampa Bay were set up using Delft3D. The models were forced with tidal and meteorological
information using inputs from a global tide model and reanalysis data. In a first step, a 63 year water
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level hindcast (A-scenario) for the period 1948-2010 in combination with a parametric bias correction
derived from a fit against existing tide gauge observations was developed. In a second step, this run
was repeated using the same boundary conditions as in the A-scenario but with Egmont Key removed
from the bathymetry (B-scenario). In a third step, the bias-corrected water levels from the A-scenario,
as well as the water level increases from the B-scenario added up on the corrected A-scenario water
levels were used to estimate return water levels. The return level assessment was conducted using the
peaks over threshold method based on the 99.8th percentile threshold exceedances.
The A-B comparison of the return water levels along the coastline of the Tampa Bay shows that Egmont
Key has a significant influence on the mainland, especially in the northern parts of the estuary. An
increase in the order of 5 cm to 17 cm for a return period of 100 years indicates that the barrier island
Egmont Key provides natural coastal protection for the mainland. Furthermore, a small increase in the
tidal range and a 20 minute time shift in the peak time series imply that the flushing of the estuary
would also be affected by a potential disappearance of Egmont Key.
Coastal Impacts of Sea Level Changes
Oral Presentations
Evaluating uncertainties in future coastal flooding occurrence as sea-level rises. Gonéri Le
Cozannet, Jeremy Rohmer, Anny Cazenave, Déborah Idiera, Roderik Van de Wal, Renske de
Winter, Rodrigo Pedreros, Yann Balouin, Charlotte Vinchon, Carlos Oliveros
As sea-level rises, the frequency of coastal marine flooding events is changing. For accurate
assessments, several other factors must be considered as well, such as the variability of sea-level rise
and storm surge patterns. Here, a global sensitivity analysis is used to provide quantitative insight into
the relative importance of contributing uncertainties over the coming decades. The method is applied
on an urban low-lying coastal site located in the northwestern Mediterranean, where the yearly
probability of damaging flooding could grow drastically after 2050. Storm surge propagation processes,
then sea-level variability, and, later, global sea-level rise scenarios become successively important
source of uncertainties over the 21st century. This defines research priorities that depend on the target
period of interest. On the long term, scenarios RCP 6.0 and 8.0 challenge local capacities of adaptation
for the considered site.
Effects of scale and input data on assessing the future impacts of coastal flooding. An application
of DIVA for the Emilia-Romagna coast. Claudia Wolff, Athanasios T. Vafeidis, Daniel Lincke,
Christian Marasmi, Jochen Hinkel
Coastal flood impacts under 21st century sea-level rise are assessed for Emilia-Romagna (Italy) using
the Dynamic Interactive Vulnerability Assessment (DIVA) modeling framework. The sensitivity of the
modeling tool to three parameters, namely (1) elevation, (2) population and (3) vertical land
movement as well as (4) to the scale of assessment are investigated. A one-driver-at-a-time sensitivity
approach was used in order to explore and quantify possible errors and uncertainties in input data and
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assessment scale on model outputs. Our results show that coastal flood impacts by the end of the
century are more sensitive to variations in elevation and vertical land movement input data than to
variations in population. The inclusion of human induced subsidence rates increases the relative sealevel by 55cm in 2100. This leads to up to two times higher coastal flood impacts compared to those
generated with the global DIVA values, which only account for natural processes. Furthermore, the
choice of one elevation model over another can result to differences of around 60% in the extent of
the coastal floodplain area and up to 70% in flood damages in 2100. These model results indicate that
variations in vertical land movement and elevation data can be very significant to the calculation of
coastal flood impacts.
The change in assessment scale was implemented via the use of a more detailed coastline and input
data (e.g. higher resolution) for the coastline segmentation process. This lead to an increase in the
number of coastal segments and a 28-fold decrease of average length per segment. Model results
show a moderate sensitivity to this change Nevertheless, we observed that the more detailed
assessment scale resulted in a more realistic spatial representation of coastal flood impacts for the
Emilia-Romagna coast. The results emphasize that different input datasets and assessment scales have
different uncertainties and implications on the results of coastal flood impact assessments. Therefore,
it is important to investigate and communicate those uncertainties in order to effectively support
decision-makers as there is a growing need to continue planning for the future, even if future
projections are not robust.
An assessment of extreme sea levels, waves and coastal flooding in the Maldives. Matthew
Wadey, Ivan Haigh, Sally Brown, Robert Nicholls
As part of a project that aims to assess impacts and vulnerability of coastal systems (at local, regional
and global scales) to sea level rise (SLR) we provide a case study of the low-lying Island nation of the
Maldives. The Maldives are regarded to imminently face the detrimental effects of SLR. We focus upon
the man-made island of Hulhumalè (adjacent to the capital, Malé) which is undergoing rapid
population growth. Our aim is to assess coastal inundation scenarios to inform practical options for
adaptation. The first objective is to assemble data on extreme sea levels, waves, past events and
defences, which includes analysis of tide gauge records and floodplain elevation maps. The second
objective is to model defence failures and inundation across a range of 21st century mean SLR
projections and extreme storm events. This includes coupling the output of a numerical wave
overtopping model to flood spreading simulations. By showing land and property affected, we analyse
these inundation scenarios in context with present-day and future coastal flooding events, and discuss
adaptation pathways.
Global and Regional Sea Level Variability and Change
Palma de Mallorca, June 10-12, 2015
Land subsidence and sea level rise at Lipari island (Italy): implications for flooding scenario.
Anzidei Marco, Bosman Alessandro, Carluccio Roberto, Carmisciano Cosmo, Casalbore Daniele,
Chiappini Massimo, Chiocci Francesco Latino, D’Ajello Caracciolo Francesca, Esposito Alessandra,
Fabris Massimo, Muccini Filippo, Nicolosi Iacopo, Pietrantonio Grazia, Sepe Vincenzo, Vecchio
Antonio
The volcanic Island of Lipari is located in the active volcanic arc of the Aeolian islands, between the
Southern Tyrrhenian Sea back arc basin (Marsili basin) and the Calabrian Arc, an orogenic belt affected
by a Late Quaternary extensional tectonics and uplift.
In this geodynamic framework, continuous and episodic GPS data collected at Lipari and nearby islands
in the time span 1996-2012, evidenced an active crustal deformations. Particularly, the vertical
component of land motion is causing the rapid subsidence of Lipari at velocities even exceeding 10
mm/yr. Instrumental data are in agreement with independent local observations based on
archaeological data, that show a continuous subsidence with rates at about 8 mm/yr since the last
2000 years B.P.
On these basis, an integrated study of this area was planned. Multibeam bathymetry with aerial digital
photogrammetry, the latter also performed locally by drone surveys, were combined to generate a
ultra-high resolution digital terrain model of land and submarine areas. The latter was extracted with
a resolution up to 0.1 m, thus supporting the creation of a detailed flooding scenario for 2100, based
on the sea level rise projections estimated from the analysis of tide gauge data collected in the central
Mediterranean in the time span 1872-2014 and IPCC reports.
Finally, relative sea level rise at Lipari is expected to cause large impacts on the environment and the
coastal installations, representing a significant hazard factor for the local population living near the
shore
Posters
Simulating overtopping and coastal flooding in urban areas: Perspectives to quantify sea
level rise effects. Sylvestre Le Roy, Rodrigo Pedreros, Camille André, François Paris, Sophie
Lecacheux, Fabien Marche, Charlotte Vinchon
Recent progresses in numerical modelling and data acquisition have allowed significant improvements
in coastal flooding simulations, with a maturity of numerical tools that now allows very precise results
in urban areas. Essentially used for hazard studies, their reliability now offers the perspective to
estimate the impact of sea level rise on coastal flooding hazards.
The presented method is based on simultaneous simulation of wave overtopping and resulting flood
in urban areas. This type of two-dimensional simulations can afford reproducing both the chronology
and the effect of urban areas on flood dynamics. The method consists in elaborating, from larger
simulations, a time-series of instantaneous water levels, including waves. This time-series is imposed
upon a time-dependent phase-resolving model to simulate dynamically wave overtopping and the
resulting flood, using a Digital Elevation Model that includes buildings.
Global and Regional Sea Level Variability and Change
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This method has been applied to the Johanna storm (2008) in Gâvres (France). SURF-WB, a NLSW
model, allowed simulating both overtopping dynamics and flooding, taking into account buildings
thanks to a 1m-resolution. Obtained results proved to be very consistent with available reports
(overtopping sectors, flooded area, water heights and chronology). This method allows reproducing
very realistically overtopping and flooding dynamics in an urban area (water heights and velocities),
with an increased accuracy and very realistic results compared to more classical approaches.
This type of simulations can be used to estimate the potential evolutions of coastal flooding processes
in a context of sea level rise due to climate change, supposing nevertheless a non-modified
morphology. Preliminary simulations realized on the site of Gâvres showed how sea level rise could
increase overtopping for a storm like Johanna. For example, a rise of 20 cm of the sea water level may
lead to a slightly larger flooded area, but with water heights increasing of about 28 cm, due to the
modifications in overtopping flows and chronology.
Tidal influence on high frequency harbor oscillations in a narrow entrance bay. S. Monserrat,
I. Fine, A. Amores, M. Marcos
High frequency sea level oscillations at Wells Harbor (Maine, Northeastern US), with periods in the
range of several tens of minutes, display a tidally modulated response. During low tides these sea level
oscillations reach amplitudes of 10-20 cm, while during high tides they are significantly smaller. Wells
Harbor is located in a low lying area with a tidal range of about 2 m and is connected to the open ocean
through a narrow channel. Thus the extent and depth of the bay significantly vary over a tidal cycle.
This changing geometry determines both the resonant periods and the amplification factor of the bay.
Numerical results confirm the link between observed variability and these specific topographic
features. Results imply that when exceptionally energetic long waves reach the Wells Harbor entrance
(as in the case of a tsunami or meteotsunami) the expected response will be significantly stronger
during low tide than during high tide. Although mean sea level would be lower in the former case, the
currents inside the bay would be stronger and potentially more dangerous. This tidally modulated
response could be extrapolated to other sites with similar topographic characteristics
A probability-based method to estimate sea level rise and future flooding risks on the
Finnish coast. Hilkka Pellikka, Milla M. Johansson, Ulpu Leijala, Katri Leinonen, Kimmo K.
Kahma
Current sea level rise scenarios are subject to large uncertainties, and decision-makers have to consider
how to incorporate the uncertainties in long-term coastal management, e.g. in determining the
building elevations of new coastal infrastructure. Preparing for the worst case is usually not costeffective. Rather, the risk level chosen should depend on the potential damage in case of flooding. To
be highly valuable for decision-making, flood risk analysis should provide estimates of flood levels with
different probabilities in the future. We present the method used to make such estimates on the coast
of Finland in the Baltic Sea.
The foundation of our calculations are the long (ca. 100 years) tide gauge records from the Finnish
coast. Historically, sea level has been declining relative to land in Finland because of postglacial land
uplift. We determine the rate of land uplift as a residual trend once the effects of global mean sea level
Global and Regional Sea Level Variability and Change
Palma de Mallorca, June 10-12, 2015
rise and changes in the wind climate have been removed from the tide gauge time series. The land
uplift is expected to continue with a constant rate for the next few centuries.
We construct a probability distribution of sea level rise in 2000-2100 using an ensemble of recently
published predictions, which have been scaled to take into account regional deviations from the global
mean. In the resulting distribution, the 5-95% range of global mean sea level rise is 33-156 cm. Regional
effects reduce the upper limit by an estimated 20-25% on the Finnish coast. By combining this
distribution with an exceedance frequency distribution of short-term sea level variations, derived from
the last 30 years of measurements, we can estimate the probabilities of different flood levels in the
future.
Combining sea state and land subsidence rates in an assessment of flooding hazards at the
Danish North Sea coast. Carlo Sørensen, Niels Broge, Per Knudsen, Ole B. Andersen
The paper presents hitherto unpublished tide gauge (TG) series from the Danish North Sea coast and
investigates their data quality and variability in mean and extreme water levels. Especially TG
benchmarks are subject to a close scrutiny as several stations are placed on sandy barriers liable to
exhibit short and longer term vertical movement, and where only recently TGs have been linked and
related to the Danish vertical datum, DVR90, making the assessment of e.g. SLR difficult. Knowledge
about sea state is important in relation to climate change (CC) effects on erosion and flooding. Here,
flooding hazards are evaluated in a case study in the town of Thyborøn that combines SLR, extreme
value analysis, and local subsidence (2-7 mm/y) and we provide (preliminary) results on the challenges
faced by the local community and their efforts opting for the best adaptation measures based on
current knowledge and projections of regional CC impacts. Sea level research and the absorption of
this knowledge into adaptation schemes in a vulnerable coastal region are discussed.
Special session on Mediterranean sea level
Oral Presentations
To what extent can Mediterranean sea level evolve differently from global sea level rise?.
Gabriel Jordà, Damià Gomis, Marta Marcos
During the last decades, Mediterranean sea level has been rising at a lower rate than the global ocean.
In addition to the recognised role of the atmospheric pressure between the 1960s and the 1990s, a
salinity increase has also been claimed as a possible mechanism to explain the lower sea level rise.
More important, it has been hypothesized that the continuous salinity increase projected by most
models could partially compensate future global sea level rise, so that by the end of the 21st century
Mediterranean sea level could be significantly lower than global sea level. These claims have generated
confusion on the fate of Mediterranean sea level under climate change.
In this presentation we will first argue why changes in the salinity of the Mediterranean Sea do not
have a significant impact on the basin averaged sea level. Furthermore we will propose a novel
approach to combine the information from global and regional models to generate a large ensemble
Global and Regional Sea Level Variability and Change
Palma de Mallorca, June 10-12, 2015
of Mediterranean sea level projections for the XXI century. The results from such projection ensemble
suggest that, independently of the emission scenario, Mediterranean sea level will evolve similarly to
the NE Atlantic. Namely, the projections show a slight increase in the baroclinic slope along Gibraltar
Strait and a small increase in the atmospheric pressure over the basin relative to the Atlantic, which
altogether would result in a decrease of about 5 cm in the Mediterranean sea level relative to the NE
Atlantic. In turn, the ensemble mean sea level shows that the NE Atlantic will be about 15 cm higher
than global mean sea level by the end of the 21st century. This altogether would result in a
Mediterranean sea level about 10 cm higher than global mean sea level.
On the connection between the sea level variability in the Mediterranean and in the Black
Seas. Denis Volkov, Felix Landerer
The Black Sea is part of a large-scale climatic system that includes the Mediterranean and the North
Atlantic. The seasonal sea level budget shows similar contributions of fresh water fluxes (precipitation,
evaporation, and river discharge) and the Black Sea outflow, while the impact of the net surface heat
flux is smaller although not negligible. We find that the nonseasonal sea level time series in the Black
and Aegean (Mediterranean) Seas are significantly correlated, the latter leading by ~1 month. This lag
is attributed to the adjustment of sea level in the Black Sea to externally forced changes of sea level in
the Aegean Sea and to the impact of river discharge. The nonseasonal sea level budget in the Black Sea
is dominated by precipitation and evaporation over the sea itself, but external processes such as river
discharge and changes in the outflow can also cause some large synoptic-scale sea level anomalies.
Sea level is strongly coupled to terrestrial water storage over the Black Sea drainage basin, which is
modulated by the North Atlantic Oscillation (NAO). We show that during the low/high NAO
southwesterly/northeasterly winds near the Strait of Gibraltar and southerly/ northerly winds over the
Aegean Sea are able to dynamically increase/decrease sea level in the Mediterranean and Black seas,
respectively.
Meteotsunamis in the Mediterranean Sea: rare but destructive extreme sea level events
occurring under specific synoptic conditions. Ivica Vilibic, Jadranka Sepic
This presentation will encompass state-of-the-art on meteotsunamis, rare but potentially destructive
extreme sea level phenomenon which occurs in the tsunami frequency band. The tsunami-like waves
are generated by atmospheric pressure disturbances propagating over a shelf, resonantly pumping
energy into the ocean during those situations in which speed of air pressure disturbance equals speed
of long ocean waves. These propagating atmospheric disturbances are normally associated with
specific atmospheric conditions which enable generation and non dissipative propagation of lowtropospheric waves over long distances.
Meteotsunamis have been documented to appear in coastal waters of all continents and world seas,
with a substantial coastal impact in low-tidal basins such as the Mediterranean. Destructive
meteotsunamis normally affect a limited area not wider than a few hundreds of kilometres; however,
the extreme events like the one occurring in the Mediterranean between 22 and 27 June 2014 may be
composed of a chain of destructive events, affecting coastal regions over a few thousands of
kilometres.
In the Mediterranean, destructive meteotsunamis are documented to occur in the Balearic Islands, the
Adriatic Sea, western Sicily coast, the Maltese Islands and the western Black Sea coast, with several
meters high waves occurring once in a decade. Meteorological tsunamis normally occur during warm
Global and Regional Sea Level Variability and Change
Palma de Mallorca, June 10-12, 2015
seasons when inflow of warm and dry air from Africa is persistent in the lower troposphere, and when
a strong and unstable mid-tropospheric south-westerly jet stream can become a dominant
atmospheric feature, serving as a generating and reflecting layer for surface atmospheric disturbances
over long distances. Damages to coastal infrastructure during destructive meteotsunami events can
be up to several millions of Euros and higher, due to both destructive sea level waves and severe
currents in harbour or bay constrictions. Meteotsunamis have also been suspected to be responsible
for a loss of human lives in an event that hit Algerian coastline in August 2007. Less prominent highfrequency events, which cause no damage, but are registered on tide gauges, occur several times a
year throughout the Mediterranean. These events may impact statistics of extreme sea levels in an
area, but can also provide an opportunity to study meteotsunamis in more detail.
Τsunami impact in the European-Mediterranean region from the antiquity up to the present.
Gerassimos A. Papadopoulos, Georgia Diakogianni, Anna Fokaefs, Antonia Papageorgiou,
Ioanna Triantafyllou
We have compiled a new tsunami catalogue covering the European and Mediterranean region from
pre-historical times up to the present containing more than 370 events with reliability assignment to
each event. An inventory of tsunami impact was created with the main attributes being the numbers
of people killed and injured, the damage to buildings, vessels, cultivated land and to other property.
The inventory includes also a record of the tsunami environmental impact, e.g. soil erosion,
geomorphological changes etc. Data on the tsunami impact were used to assign tsunami intensity in
the 12-point Papadopoulos-Imamura (2001) scale for the majority of the events listed. The tsunami
impact was studied as for its space and time distribution. In space, the tsunami impact was mapped in
terms of tsunami intensity and impact zones were determined. The time distribution of the tsunami
impact was examined for each one of the impact zones. It has been found that the main impact comes
from extreme, earthquake tsunamigenic events, such the ones of AD 365 in Crete, 551 in Lebanon,
1303 in Crete, 1755 in Lisbon. However, high impact may also occur from events of lower magnitude,
such as the ones of 1908 in Messina straits and 1956 in the South Aegean, which underlines the strong
dependence of the impact on the community exposure. Another important finding is that the
cumulative impact of relatively moderate or even small, local tsunamis, regardless of their generation
mechanisms is quite important and that such distributed tsunami impact should not be neglected in
actions undertaken for the tsunami risk mitigation. This research is a contribution to the EU-FP7
tsunami research project ASTARTE (Assessment, Strategy And Risk Reduction for Tsunamis in Europe),
grant agreement no: 603839, 2013-10-30.
Evolution of sea level and other variables on the XXI century: a picture derived from
Vanimedat II and ESCENARIOS projects. Enrique Álvarez Fanjul, Damià Gomis, E. RodríguezCamino, Marta Marcos, Gabriel Jordà, R. Aznar, J. C. Sánchez-Perrino, A. Martínez Asensio,
J. Llasses, Elena Padorno, Begoña Pérez, M. N. Tsimplis, F.M. Calafat, Samuel Somot, F.
Sevault, F. Adloff, J. M. Rodríguez
An overview of the results of climate change studies on the Mediterranean Sea, made over the last
decade in the framework of Vanimedat II and SCENARIOS projects, is presented. The evolution of the
main marine physical variables (waves, sea level, currents, water temperature and salinity) is analyzed,
as well as changes in atmospheric variables with important impact on marine dynamics (heat and fresh
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Palma de Mallorca, June 10-12, 2015
water fluxes, wind and atmospheric pressure). In order to fulfill this objective, long term numerical
simulations have been carried out: WAM has been employed for reproducing wave dynamics, Nivmar
for sea level residual, RCA for atmosphere and NEMO for sea level, circulation and hydrography.
Integration domains cover all the Mediterranean Sea. The model runs have been nested, when it has
been necessary, into the results of global models generated by other institutions. New methodologies
have been developed to cope with the treatment of sea level data provided by nested 3D baroclinic
models. More specifically, the problem of dealing with changes into the mass flows has been
addressed. In order to obtain a more complete view of the evolution of certain variables, previously
existing simulations from other institutions have been included into the analysis. As a result of the
works, a consistent high resolution description of the evolution of climate change on the Spanish coast
has been obtained. The simulations describe a significant increase in mean sea level and SST, as well
as minor changes in the wave regime. The evolution of salinity is conditioned by changes in the
boundary conditions from global model, which vary significantly from one simulation to another. These
results are consistent with those from the IPCC, but provide a detailed high resolution view over the
Mediterranean Sea. The scenarios obtained show the need to develop adaptation policies on our
shores.
Future evolution of sea level extremes along the Mediterranean coastline as produced by
the superposition of storminess and sea level rise. Piero Lionello, Dario Conte, Luigi Marzo,
Luca Scarascia
The maximum water level that water reaches at the coast during a storm depends on several factors:
change of mean level (in turn depending on regional steric effects and on remote melting of ice caps),
wave heights, storm surge level. This study attempts to estimate the overall maximum water level by
a simple linear superposition of these factors along the coasts of the Mediterranean Sea. This is a
particularly interesting case as these factors act in opposite directions: sea level is expected to increase
(though the actual future level is uncertain) while reduction of storminess is expected to decrease
future surges and wave height maxima. It is shown that if water mass addition across the Gibraltar
Strait will produce a 10cm sea level rise in the Mediterranean Sea, this contribution will compensate
for the reduction of storminess on water level maxima until mid 21st century. However, if mass
addition will contribute a 20cm sea level rise, then water level maxima during storms will significantly
increase along more than 75% of the Mediterranean coastline.
Posters
Sea level at 2ka BP in the Balearic Islands from Roman age coastal quarries. Fabrizio
Antonioli, Marcus Heinrich Hermanns, Marco Anzidei
Along the coasts of Ibiza and Mallorca (Balearic Islands, Spain) have been identified submerged coastal
quarries of roman age which are of great interest for the study of the relative sea level changes during
the last millennia. These were carved on sedimentary carbonate coasts, as in other sites of the
Mediterranean basin, at elevation above sea level. Here we show the results of observations and
measurements collected at the four sites: Sain Jordan in Mallorca, Port d'es Torrent, Ses Portes and
Cap Jueu at Ibiza. Once field observations have been corrected for tide amplitudes at the time of the
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Palma de Mallorca, June 10-12, 2015
surveys by tide gauge data from the nearest stations, lowest cuttings were placed at elevations
between -0.7 and -0.3 meters. Since the Balearic islands are located in a tectonically stable region, the
elevation of the quarries, after they have been interpreted for their functional elevations, are in
agreement with a sea level at 2ka BP lowers than today of about 1.3 m, in good agreement with the
estimates of Lambeck and Purcell (2005). These observations, that are in contrast with Dorhale et al.
(2010), suggest that since the last 2 ka the Balearic Islands underwent to glacio-hydro-isostatic
movements similar to Sardinia, in absence of significant tectonic events.
Sensitivity of the Mediterranean sea level to atmospheric pressure and free surface
elevation numerical formulation in NEMO. Antonio Bonaduce, Paolo Oddo, Nadia Pinardi,
Antonio Guarnieri
The sensitivity of the dynamics of the Mediterranean Sea to atmospheric pressure and free surface
elevation for- mulation using NEMO (Nucleus for European Modelling of the Ocean) was evaluated.
Four different experiments were carried out in the Mediterranean Sea using filtered or explicit free
surface numerical schemes and account- ing for the effect of atmospheric pressure in addition to wind
and buoyancy fluxes. Model results were evaluated by coherency and power spectrum analysis with
tide gauge data. We found that atmospheric pressure plays an important role for periods shorter than
100 days. The free surface formulation is important to obtain the correct ocean response for periods
shorter than 30 days. At frequencies higher than 15 days−1 the Mediterranean basin’s response to
atmospheric pressure was not coherent and the performance of the model strongly depended on the
specific area considered. A large-amplitude seasonal oscillation observed in the experiments using a
filtered free surface was not evident in the corresponding explicit free surface formulation case, which
was due to a phase shift between mass fluxes in the Gibraltar Strait and at the surface. The
configuration with time splitting and atmospheric pressure always performed best; the differences
were enhanced at very high frequencies.
Rescuing historic Maltese tide gauge data. Elizabeth Bradshaw
The British Oceanographic Data Centre (BODC), through funding from the UK Department for Business,
Innovation and Skills (BIS) 'Breakthrough Fund' have scanned tidal charts from Valletta, Malta (18761926), which were in the archive of the United Kingdom Hydrographic Office (UKHO). The analogue
records were difficult to access and in need of conservation. They have now been conserved and
photographed to produce digital images and these images will be publically available from
www.bodc.ac.uk/data/online_delivery/historical_uk_tide_gauge_data/, preserving one of the longest
and earliest temporal series of sea level data in the Mediterranean.
A vital component of climate change research, long-term sea level records are used to identify global
and regional sea level changes and the changing frequency of storm surges and coastal floods. The
data are used by the Intergovernmental Panel on Climate Change (IPCC) in their reports, which inform
policy on our changing weather. Historical data are unrepeatable measurements and we want to
encourage their rescue and re-use, especially from data-sparse regions. There are no long-term sea
level records in the middle of the Mediterranean, and only one with 50 years of data in the Southern
Mediterranean in the Permanent Service for Mean Sea Level data bank.
Global and Regional Sea Level Variability and Change
Palma de Mallorca, June 10-12, 2015
We are investigating digitising the images via a citizen science activity, such as the International
Environmental Data Rescue Organization (IEDRO) project, Weather Wizards, where citizen scientists
are helping to digitise pluviograms (rainfall charts). If possible, this system could be adapted for tide
gauge charts.
Once the record is digitised, it can be studied to help refine models of climate change, surges and
tsunami propagation in the Mediterranean.
BODC have been working with the Global Sea Level Observing System Group of Experts (GLOSS GE) on
sea level data archaeology (unearthing, preserving, digitising, quality controlling and distributing
historical data) - www.gloss-sealevel.org/data/glossdataarchaeology.html
Long-wave analysis of coastal sea-level records and implications for hazard monitoring and
assessment: an application to the Siracusa, Italy, tide-gauge station. Lidia Bressan, Stefano
Tinti
The Siracusa tide-gauge station is part of the TSUNET network, a sea-level monitoring network to
measure and detect tsunamis in Eastern Sicily, one of the most hazardous coastal areas for tsunamis
in the Mediterranean sea. Detection of tsunamis and other anomalous wave conditions is carried out
by using a specific package called TEDA developed by the Tsunami Research Team of the University of
Bologna, Italy. TEDA is a real-time detection algorithm for long period waves structured in two
algorithms that work in parallel: i) the tsunami detection method that detects impulsive long period
waves, like tsunamis, and that it is based on a modified STA/LTA algorithm working on the detided sealevel instantaneous slope IS and on the background slope BS; and ii) the secure detection method that
computes the detided secure detection marigram (MSD) and identifies waves exceeding a certain
amplitude threshold.
In this work, also exploiting the specific TEDA functions, we analyze the tide-gauge records of Siracusa.
It is found that the sea-level presents a typical spectral content due to the regional and local coastal
morphology and bathymetry, which is reflected also in the functions IS and MSD. The station exhibits
spectral stability on an annual basis, and seasonal variability, with more energetic spectra in winter
months and quieter spectra in summer.
A further analysis focused on the empirical frequency distribution (EFD) of the TEDA characteristic
functions, confirms the annual stability and seasonal variability. Interestingly, it is found that the EFDs
computed on a monthly or longer-interval basis fit well-known probability density functions, which
helps to study the seasonal variations of the sea-level and calls for a theoretical interpretation. The
results of the analysis are presented and discussed.
Mesoscale eddies in the Western Mediterranean Sea. Romain Escudier, Ananda Pascual,
Pierre Brasseur, Lionel Renault
Mesoscale eddies are relatively small structures that dominate the ocean variability and have large
impact on large scale circulation, heat fluxes and biological processes. In the western Mediterranean
Sea, a high number of eddies has been observed and studied in the past with in-situ observations. Yet,
a systematic characterization of these eddies is still lacking due to the small scales involved in these
Global and Regional Sea Level Variability and Change
Palma de Mallorca, June 10-12, 2015
processes in this region where the Rossby deformation radius that characterizes the horizontal scales
of the eddies is small (10-15 km).
The objective of this study is to perform a characterization of mesoscale eddies in the western
Mediterranean. In this objective, we develop a high resolution simulation of the area. Then we apply
three different eddy detection and tracking methods to extract eddy characteristics from the outputs
of the high-resolution simulation, a coarser simulation and altimetry maps. The results allow the
determination of some characteristics of the detected eddies. The size of eddies can greatly vary but
is around 25-30 km. About 30 eddies are detected per day in the region with a very heterogeneous
spatial distribution. Unlike other areas of the open ocean, they are mainly advected by currents of the
region. Eddies can be separated according to their lifespan. Long-lived eddies are larger in amplitude
and scale and have a seasonal cycle with a peak in late summer, while short-lived eddies are smaller
and more present in winter. The penetration depth of detected eddies has also a large variance but
the mean depth is around 300 meters. Anticyclones extend deeper in the water column and have a
more conic shape than cyclones.
Improved satellite altimeter mapped sea level anomalies in the Mediterranean Sea. Marta
Marcos, Ananda Pascual, Isabelle Pujol
The new gridded Mediterranean sea level anomaly product recently released by AVISO (DT14) is
evaluated and compared with the earlier version (DT10) at which it is aimed to substitute. Differences
between the two products are found along coastal regions, where the new version captures more
variability (up to 10% more) and trends locally differ by up to 1 mm/yr for the altimetric period. Coastal
tide gauge observations have therefore been used as the basis for quantifying changes in DT14.
Correlation and variance reduction in available monthly tide gauge time series are improved in more
than 80% of the selected sites, resulting in an overall higher skill to recover coastal low frequency sea
level signals. Results for higher/lower order percentiles were also explored and showed different
performances depending on the site, although with a slight overall improvement. A comparison with
tide gauges on a daily basis using wavelet analysis reveals that altimetry gridded products are still far
from recovering higher frequency coastal sea level signals despite some advances have been achieved
thanks to the daily temporal sampling of DT14.
Determination of Mean Dynamic Topography over the Mediterranean Sea from Jason-2
Altimetry Measurements and EGM2008 Data. Ali Rami, Sofiane Khelifa
The ocean surface must be surveyed in order to determine the dynamic topography, tides, timevariations etc…
The ocean dynamic topography, which is the distance between the geoid and the instantaneous sea
surface height and which reflects the ocean dynamics, is a primary oceanography unknown.
The processing of 5 years of Jason-2 satellite altimetry measurements is done after the estimation of
the environmental geophysical and orbital parameters corrections, permit us to determinate the sea
surface height with 1 cm of precision, while using the Earth Gravitational Model EGM2008 (geoid)
based on a combined data (GRACE, terrestrial and altimetry measurements,….) we can calculate the
Global and Regional Sea Level Variability and Change
Palma de Mallorca, June 10-12, 2015
mean dynamic topography of the Western Mediterranean sea. The variation of the obtained mean
dynamic topography is between -1.12 and 1.12m.
The obtained surface is compared with the Mean dynamic topography provided by AVISO Altimetry
(RioMed).
Interannual variability of the Surface Geostrophic Circulation of the Mediterranean Sea. M.
Sempere, S. Esselborn, I.Vigo
The most recent advances in the geoid determination, provided by the Gravity Field and Steady-State
Ocean Circulation Explorer (GOCE) mission, together with the continuous monitoring of the sea surface
height by the altimeters on board of satellites have made possible to retrieve ocean surface currents
directly through remote sensing. A reliable estimation of the ocean Dynamic Topography (DT) that, in
turn, requires reliable measurements of the Absolute Sea Level (ASL) height and an independent geoid
are the key to the determination of the Surface Geostrophic Currents (SGC). Nowadays it is possible
to combine more than 20 years of altimetry data with a geoid model based on GOCE data to obtain
the DT with an unprecedented precision and accuracy. In addition, the improved accuracy in satellite
altimetry data has allowed to determine ASL maps at weekly resolution.
New insights into the structure and variability of the Mediterranean Sea's surface circulation are
obtained through the analysis of the long series, for the period spanning 1992–2014, of weekly SGC
maps gridded at one eighth degree longitude and latitude resolution resolving spatial scales as short
as 70 km. For presentation, this data set is averaged monthly and the results are interpreted and
validated with simulations from ECCO/Mercator models and/or drifter observations where possible.
Seasonal Cycle of Surface Geostrophic Circulation of the Mediterranean Sea. M.Sempere, I.
Vigo, M. Trottini, S. Esselborn
The most recent advances in the geoid determination, provided by the Gravity Field and Steady-State
Ocean Circulation Explorer (GOCE) mission, together with the continuous monitoring of the sea surface
height by the altimeters on board of satellites have made possible to retrieve ocean surface currents
directly through remote sensing. A reliable estimation of the ocean Dynamic Topography (DT) that, in
turn, requires reliable measurements of the Absolute Sea Level (ASL) height and an independent geoid
are the key to the determination of the Surface Geostrophic Currents (SGC). Nowadays it is possible
to combine more than 20 years of altimetry data with a geoid model based on GOCE data to obtain a
the DT with an unprecedented precision and accuracy. In addition, the improved accuracy in satellite
altimetry data has allowed to determine ASL maps at weekly resolution.
In this work, weekly SGC maps of the entire Mediterranean Sea for the period spanning 1992–2014
gridded at one eighth degree longitude and latitude resolution resolving spatial scales as short as 70
km are used to extend previous research on the Mediterranean surface circulation seasonality. To
investigate the annual and semiannual cycles in SGC, we least squares fitted the corresponding
harmonics independently for each velocity component. For presentation, the data sets are averaged
monthly and the results are interpreted and validated with simulations from ECCO/Mercator models
and/or drifter observations where possible.
Global and Regional Sea Level Variability and Change
Palma de Mallorca, June 10-12, 2015
High-frequency sea-level oscillations in the Mediterranean Sea: analysis and synoptic
preconditioning. Jadranka Sepic, Ivica Vilibic, Amaury Lafon, Loic Macheboeuf, Zvonko
Ivanovic
During the last decade many national tide gauge networks have been upgraded to measure sea level
with a higher sampling rate (1-min). Concurrently, through a number of tsunami warning systems and
data sharing services, these data became freely available to scientific community, allowing for regional
and ocean studies of high-frequency component of sea level oscillations.
Presented study focuses on an analysis of 1-min sea level time series collected at 32 Mediterranean
tide gauge stations with 4 or more years of data available between 2008 and 2014. The data is available
at the IOC website (http://www.ioc-sealevelmonitoring.org). Sea level time series were de-spiked, detided, linearly interpolated, high-pass filtered and analysed. Several important points were revealed:
(i) high-frequency sea level oscillations are often widespread and can affect areas from the eastern
Spanish to the western Greek coast; (ii) during the Mediterranean-wide events, oscillations typically
first occur in the Western Mediterranean, and then their occurrence propagates within the next few
days to the Eastern Mediterranean (Greece); (iii) oscillations occur throughout the year but are,
depending on area, strongest from April to August; and (iv) high-frequency sea level oscillations are
often associated with higher-than-average mean sea level conditions, adding to a possible danger of
flooding; also, they are occasionally related to dangerous meteotsunami events.
Synoptic conditions observed during the 48 strongest events were analysed in more detail. These
events typically occur during: (i) presence of low mean sea level pressure with a centre northwest from
the affected area; (ii) inflow of warm African air in the lower troposphere; (iii) strong south-western
winds and the jet at mid-tropospheric levels embedded in (iv) instable atmospheric levels. Analysis of
sea level data combined with statistics of appearance of favourable synoptic pattern has a potential to
further contribute to the flooding hazard assessment.
Mean sea level secular trends from PSMSL RLR data: A case study for the Mediterranean
basin. Hebib Taibi , Mahdi Haddad
In this paper, Dynamic Harmonic Regression (DHR) model is applied to the investigation of the longterm evolution of sea level time series monitored in Mediterranean coastal areas and recovered from
the Permanent Service for Mean Sea Level (PSMSL) database.
The analysis of 9 long monthly mean sea level series indicate that the Mediterranean mean sea level
has significantly been raised during the last century. The various results obtained in this paper are
promising and show that the sea level behavior in different stations is far from uniform. As extremity,
while in Split - Gradska Luka station, the sea level has indeed risen during the period 1955-2008 by up
to 0.43 ± 0.06 mm/year, the sea level Venezia (Punta Della Salute) has raised with a rate of 3.01 ±
0.03mm/year during the period 1909-2000.
Relative sea level trend and long term variability in the Northern Mediterranean from tide
gauge data: implications for future projections. Antonio Vecchio, Marco Anzidei
We analyzed the longest tidal records available for the Mediterranean region at eight tide gauge
stations distributed along the coasts of Italy, France, Slovenia and Croatia. Data were retrieved from
Global and Regional Sea Level Variability and Change
Palma de Mallorca, June 10-12, 2015
the Permanent Service for Mean Sea Level and were collected in the 1872-2014 time span for the tidal
stations of Genova and Marseille. From these long records we identified the contributions of the
nonlinear global warming signal and the long term natural variability in the sea level trend. Through
the development of a simple low order theoretical model we investigated the combined effect of the
global sea level increase and the decadal natural variability on the future sea levels at the analyzed
stations. Finally, we tentatively estimated the future sea level rise up to 2100, by including the IPCC
predictions in our analysis. Here we show and discuss the expected sea levels at the individual stations
that will have implications for coastal flooding of lowland areas located in the investigated region.