How to „calibrate“ speleothem proxy data: a critical review Christoph Spötl University of Innsbruck, Austria OUTLINE: The cave archive Quantifying palaeo rainfall Quantifying palaeo temperature To-do list Soda straws Stalactites Drapery Column Stalagmites Flowstone Foto: D. Bunnell Uncertainty Age <1-2% 0.3kyr 5kyr 10kyr 20kyr 50kyr Fleitmann pers. comm. 5,2m Uamh an Tartair Ernesto Crag Villars Spannagel Korallgrottan Soreq Corchia Peqiin Hoti Qunf Argentarola Hulu Gibraltar Sanbao Dongge Makapansgat Carlsbad Sagittarius Moomi Bukit Assam Snail Shell Santana Moondyne Botuverá Fairchild et al. (2007; modified) Uncertainty smoothing & delay (h-y) Fairchild et al. 2006 (mod.) Uncertainty δ18O <0.1‰ δ13C <0.1‰ H2Ometeoric ppt CO2(atm) Atmosphere Biosphere CO2(soil gas) Soil Limestone CaCO3 DICseepage water Cave CaCO3 CO2(cave air) H2O Mid latitudes Low latitudes Warm climate - moderately high growth rate - high δ18O - low δ13C Wet climate - very high growth rate - low δ18O - low δ13C Cool climate - very slow growth rate - low δ18O - high δ13C Dry climate - slow growth rate - high δ18O - high δ13C Glacial climate - no speleothem formation - cave flooding or ice fm. Wang et al., Nature 2008 Hu et al. EPSL 2008 Hu et al. EPSL 2008 Hu et al. EPSL 2008 Uncertainty modern ppt-δ18O relationship Hu et al. EPSL 2008 Uncertainty Age model Hu et al. EPSL 2008 Uncertainty lamina counting: <20 yr Proctor et al. Clim. Dyn. 2000 Annual band width = -4.637 + 1508 (T/P), r = 0.80 Proctor et al. Clim. Dyn. 2000 Mattey et al. EPSL 2008 Mattey et al. EPSL 2008 Mattey et al. EPSL 2008 Uncertainty modern ppt-δ18O relationship Mattey et al. EPSL 2008 Uncertainty Age model Lauritzen & Lundberg, Holocene 1999 Uncertainty sampling resolution: 20 yr Lauritzen & Lundberg, Holocene 1999 Lauritzen & Lundberg, Holocene 1999 Uncertainty long-term tempδ18O relationship Lauritzen & Lundberg, Holocene 1999 Lauritzen & Lundberg, Holocene 1999 Moberg et al., Nature 2005 Frisia et al., EPSL 2003 Lamina thickness Lamina thickness, normalised of variance corr. coeff. with temp. at Milano corr. coeff. with ppt. at Milano Frisia et al., EPSL 2003 corr. coeff. with temp. at Milano corr. coeff. with ppt. at Milano Frisia et al., EPSL 2003 Smith et al., Int. J. Clim. 2006 Smith et al., Int. J. Clim. 2006 Where we stand • Speleothems provide excellent chronologies on climate change in certain regions • Speleothems capture low- to high-frequency climate variability depending on the cave setting • Speleothem records primarily reflect the local microclimate (modulated by the hydrogeology) • Most speleothem records rely on O isotope data as the main climate proxy and are qualitative only Where we stand • Calibration of O isotope data is limited to the past max. 40 yr • Direct in-cave on-site calibration is essential, but may not capture the full range of the proxies for long-term climate reconstructions • Calibration uncertainties are likely significant but no protocol currently exists Uncertainties: action points • Assess local variability: replication of speleothem records from the same cave • Assess regional variability: replication of speleothem records from different caves • Validate climate-δ18O calibration: comparison with O isotope data from other archives Uncertainties: action points • Assess the coherence of speleothem (and other) proxy records and climate on a mesoscale: regional climate models including isotopes • Comparison with new emerging speleothem proxies • Collaboration with statisticians --> SUPRAnet