1. science

Diedrich Fritzsche1([email protected]), Thomas Opel1, Hanno Meyer1,
Silke Merchel2, Georg Rugel2, Santiago Miguel Enamorado Baez2
1
Alfred Wegener Institute for Polar and Marine Research, Potsdam, Germany
2
Helmholtz-Zentrum Dresden-Rossendorf,
Helmholtz Institute Freiberg for Ressource Technology, Dresden, Germany
Late Holocene environmental ice core record
from Akademii Nauk ice cap (Severnaya Zemlya)
Paleoclimate Proxies
Introduction
Major Ions
Severnaya Zemlya
Stable-water Isotopes
Akademii Naukiceice
cap
cap
18
d O record of AN ice core
all annual data - grey
A: Surface air temperature
(SAT) variations compiled for
Atlantic/Arctic boundary region
[4], 5 years running means
(yrm) - green, AN d18O, 5 yrm
(red) and meteorological SAT
data from Vardø/ Northern
Norway, 5 yrm ( blue).
MSA (ppb)
Austfonna
Akademii Nauk
Vardø
Map of the Arctic
B: AN d18O, 15 yrm (red) and
Austfonna d 1 8 O (Svalbard)
[5],15 yrm (blue.)
Inset : Severnaya Zemlya with
Akademii Nauk ice cap and drilling
site (80º31’N 94º49'E). L o c a t i o n s
referred to this poster are labelled.
In the Arctic, a key region for the global climate system and more
affected by the ongoing warming than other regions,
meteorological records are relatively short, with only a few time
th
series starting before the 20 century. Hence, climate archives,
especially high-resolution ones like ice cores, are of particular
importance for the assessment of past and recent climate
changes.
To gain new high-resolution proxy data for the reconstruction of
climate and environmental changes, a 724 m-long ice core was
drilled near summit of Akademii Nauk (AN) ice cap, the largest
glacier on Severnaya Zemlya (Figure above) within a joint
German - Russian project in 1999-2001 [1]. In the Eurasian
Arctic Severnaya Zemlya is the easternmost archipelago
covered by considerable ice caps.
The AN ice cap is affected by melting in summertime.
Percolating water causes alterations of original isotope and
chemical signals.
Major ions have been analysed in low resolution only (bagmean values - figure left). Volcanoes used for core dating are
marked but are missing in the lower core part. Therefore, we
tried an independent validation of our age-depth relationship
10
using Be concentrations (below).
The figure above shows the d18O record of the upper 255 m
using our preliminary dating. We found the best correlation with
Arctic meteorological time series for Vardø, Northern Norway
18
(r5yrm = 0.76). Therefore, we consider our d O 5yrm data as a
robust temperature (SAT) proxy showing features typical for the
Western Eurasian Arctic. Examples are the double-peaked
Early Twentieth Century warming (1920-1940) and the absolute
SAT minimum just before 1800 also found in the Austfonna d18O
ice core record from Svalbard [6]. The SAT reconstruction for
the Atlantic-Arctic boundary region [4] shows remarkable
differences.
Record of bag-mean values of major ions
Sulphate record shows prominent peaks corresponding to volcano
eruptions of Bezymianny 1956 (1), Katmai 1912 (2), Laki 1783 (3), Samalas ?
1257 (4) and Eldgja 934 (5) used as reference horizons for core dating. The
20th century pattern of sulphate and nitrate reflects anthropogenic
emissions.
+
Sea-salt ions (e.g. Na , methanesulphonate MSA ) show a decreasing trend
between 300 and 1800 probably caused by the increase of surface elevation
at the drilling point followed by a strong increase around 1910, indicating an
abrupt shift in sea-ice atmosphere interactions (nss = none sea-salt).
Core Dating
10
Validation of Core Dating
10
Be is one of several radionuclides produced in the Earth's
atmosphere by cosmic radiation. Because its production rate is
modulated by variations of geo- and heliomagnetic fields the
concentrations of these nuclides in glacier ice or tree rings are
suitable to reconstruct solar activity. Vice versa an ice core age
10
model can be verified by matching Be concentrations with
cosmogenic radionuclide records from well-dated archives.
Local differences in 10Be ice core records as results of different
geomagnetic coordinates, transport and deposition processes
and accumulation rates are known [7] and have to be
considered. After 1600 AD AN 10Be concentration maxima fit well
with periods of relative quiet sun (known as Gleisberg (G),
Dalton (D), Maunder (M) and Spörer (S) Minima) visible in 14C
production [8] and 1.PC derived by PCA of 10Be records from
NGRIP, Dye3 (both Greenland) and South Pole ice cores [9],
too. An explanation for the yet obvious mismatching before
1600 needs further investigations.
Age (years before 1999)
5000
4500
4000
3500
3000
2500
2000
1500
1000
500
0
0
4.5E+4
3
AN10Be
AN 10Be 5rm
4.0E+4
100
Nye model
Model
Nye
Sample age
1105)
Sample
age(Dating
(Dat.2013)
Nye model
(modified)
Nye
(modified)
volcano references
Volcano
references
137
Cs references
137Cs
references
300
400
3,0E+4
AN 10Be [atoms/g]
200
Depth
w.e.)
Depth (m w.e)
3.5E+4
500
Basal ice
S
M
D
10
BeNGRIPDye3SP1PC
14
C production
.
2.5
G
2
2.5E+4
2.0E+4
1.5
1.5E+4
1.0E+4
1
5.0E+3
600
0.0E+0
0.5
Age-depth relationship of the core
6E+4
10
AN Be
4.5E+4
10
AN Be 5rm
10
Dye3 Be
5E+4
4.0E+4
10
Dye3 Be121rm
4E+4
3.0E+4
2.5E+4
3E+4
2.0E+4
2E+4
Dye3 10Be [atoms/g]
3.5E+4
AN 10Be [atoms/g]
An exact core chronology is essential to interpret paleoenvironmental signals. For the upper 479 m dating has been
done by counting annual cycles of stable water isotopes
(magenta in Figure above). For cross-checking we used peaks
137
of Cs (Chernobyl 1986), nuclear weapon tests (1963) [2] as
well as 5 volcanic reference horizons (cf. Figure Major Ions).
Our dating shows that the glacier has not been in dynamical
steady state in the past as postulated by usual standard flow
models such as Nye‘s [3] - blue line - but it has been growing
until recent times. A modified Nye model considering the
increasing surface altitude has been developed - red line - and
was used for dating of deeper core sections. Our model predicts
an age of about 3100 years at a depth of 690 m (630 m water
equivalent - w.e.). The deepest core part (Figure below) has
completely different properties hence, we suppose an
unconformity at this depth.
Be
1.5E+4
1.0E+4
1E+4
5.0E+3
0E+0
0E+0
10
Comparison of Be concentration in AN with 1. PC (PCA) [9] from
10
high-resolution Be records from NGRIP, Dye3 and South Pole
10
ice cores (above) and Be from Dye3 core (below).
AMS measurement
10
6
Be decays (beta decay) with a half-life of 1.387 *10 years,
which usually requires long measuring times at low sensitivity
for beta-spectroscopy. Thus only Accelerator Mass Spectrometry (AMS) is sensitive enough for the effective measure of
10
Be concentrations in ice cores. The Ion Beam Center of HZDR
offers determination of cosmogenic radionuclides using a highenergy accelerator (voltage 6 MV, figure below). The team of
10
DREsden AMS (DREAMS) [10] was able to measure Be
concentrations in discrete AN ice core samples of about 300 g
each.
bouncer magnet
• sequentially isotope injection
• switching frequency: ~100 Hz
1 µm thick Si3N4
absorber foil
energy analyser 54° E.S.A.
35° E.S.A.
vertical 30° magnet radius: 2.6 m
pole gap: 36 mm
4-anode gas
ionisation detector
Deepest core section with debris
two movable
offset FCs
90° magnet
radius: 1.5 m
pole gap: 40 mm
185 MeV amu
6 MV HVEE Tandetron
• Cockcroft-Walton type
• terminal voltage: 0.3 – 6 MV
• argon stripper gas
• no corona stabilization needed
DREAMS (DREsden AMS): Machine layout (E.S.A. = electrostatic analyser)
References:
[1] Fritzsche et al. 2002, Ann. Glaciology 35, doi: http://dx.doi.org/10.3189/172756402781816645; [2] Pinglot et al. 2003, J. Glaciology 49, doi: http://dx.doi.org/10.3189/172756503781830944; [3] Nye 1963, J. Glaciology 4, 785-788;
[4] Wood et al. 2010, GRL 37, doi:10.1029/2010GL044176; [5] Isaksson et al. 2005, Geogr. Annaler 87A, doi: 10.1111/j.0435-3676.2005.00253.x; [6] Opel et al. 2013, Climate of the Past 9, doi:10.5194/cp-9-2379-2013;
[7] Berggren et al. 2009, GRL 36, doi:10.1029/2009GL038004; [8] Muscheler et al. 2005, Quaternary Science Reviews 24, doi:10.1016/j.quascirev.2005.01.012; [9] Steinhilber et al. 2012, PNAS 109, doi: 10.1073/pnas.1118965109;
[10] Akhmadaliev et al. 2013, NIMB 294, doi: 10.1016/j.nimb.2012.01.053
two AMS ion sources