Losch, M.

Mulitza, S.

Paul, A.

English

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The MARGO (Multi-proxy Approach for the Reconstruction of the Glacial Ocean Surface) sea-surface temperature (SST) reconstruction for the Last Glacial Maximum (LGM,~23,000-19,000 a before present) has been criticized to yield a low estimate of the fast-feedback climate sensi- tivity of less than 3 °C for a doubling of the atmospheric CO2 concentration.  MotivationConclusions1.The estimated global surface change in δ18Ow of 0.9 ‰ ± 0.1 ‰ agrees with the global average change estimated by Labeyrie et al. (1987), Adkins et al. (2002) and Duplessy et al. (2002).2.Thus the global mean cooling implied by the MARGO annual-mean SST anomaly, albeit uncertain, appears to be consistent with the MARGO oxygen isotope ratios measured on planktic foraminifera δ18Oc.3.This gives support to the MARGO SST reconstruction, without necessarily implying a low climate sensitivity.● Combined oxygen isotope ratios measured on planktic foraminifera δ18Oc (Fig. 1, 2) with published MARGO SST anomaly for LGM  (Fig. 3).● Used variational method “Data-Interpolating Variational Analysis” (DIVA – Troupin et al.) to estimate MARGO SST anomaly including error field.MethodsEstimates of global ocean cooling at the Last Glacial Maximum based on sea-surface temperature and oxygen-isotope reconstructionsAndré Paul1, Stefan Mulitza1, Martin Losch2 and MARGO Isotope Group(1) MARUM - Center for Marine Environmental Sciences and Department of Geosciences, University of Bremen, Bremen, Germany (apaul@marum.de)(2) Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, GermanyFig. 3 MARGOsummer (JAS) SST anomaly between LGMand late Holocene.EGU2012-9198www.glacialoceanatlas.orgwww.marum.de/en/OC5.htmFig. 1 MARGO  isotope data.Core topsLast GlacialMaximumFig. 2 Species-specific difference  Δδ18Oc between LGM and late Holocene.Results● Global change in analyzed SST 1 °C with large uncertainty and in surface δ18Ow  at core locations 0.9 ‰ ± 0.1 ‰.● Regional patterns in Δδ18Oc (Fig. 2) similar to SST anomaly (Fig. 3), e.g. in the Mediterranean.Individual error (1σ): ±0.1 ‰● Preliminary variational analysis using DIVA yields small global SST cooling with large uncertainty due to large regions void of data.● However, climate models consistent with the MARGO SST data (Hargreaves et al., 2011) still show a global cooling larger than 3 °C; those that simulated best the MARGO LGM SST reconstruction have a medium climate sensitivity between 2.8 °C and 3.3 °C for a doubling of the atmospheric CO2 concentration (Otto-Bliesner et al., 2009).● In contrast, the “adjoint method” applied to a simplified climate model gives a low climate sensitivity of 2.2 °C to 2.5 °C (Fig. 4 – cf. Paul and Losch, 2012).DiscussionFig. 4 Classical EBM fitted to data from GLAMAP 2000 project (Sarnthein et al., 2003). Control variables: radiative forcing parameter ΔQ2xCO2 and diffusion coefficients.5°x5° blockaveragesDIVA analyzed field on 1°x1° gridDIVA error field on 1°x1° grid

Estimates of global ocean cooling at the Last Glacial Maximum based on sea-surface temperature and oxygen-isotope reconstructions

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