Comparing proxies for the reconstruction of LGM sea-surface conditions in the northern North Atlantic

Within the frame of the multiproxy approach for the reconstruction of the glacial ocean (MARGO) project, sea-surface conditions of the Last Glacial Maximum (LGM, 23-19 ka) were reconstructed using different proxies, which were calibrated to a standardized modern hydrography. In the North Atlantic, the revised LGM MARGO data set provides a comprehensive coverage, including the Nordic Seas. The data set includes reconstruction based on planktonic foraminifer assemblages, dinocyst assemblages, alkenone coccolithophorid biomarkers and Mg/Ca ratios in planktonic foraminifers. Several hydrological features of the LGM North Atlantic can be identified, that are supported by all four proxies. They include an extensive perennial sea-ice cover along the eastern Canadian and Greenland margins, seasonally ice-free central North Atlantic and Norwegian Sea, and the winter sea-ice limit being located at about 55 degrees N. All proxies also suggest significantly colder than modern sea-surface conditions in the southeastern part of the North Atlantic and a more zonal temperature pattern than at present, with a steep SST gradient of the order of 10 degrees C between 40 degrees N and 45 degrees N. However, in the Nordic Seas large discrepancies remain, well above the level of uncertainty of the SST reconstructions. These discrepancies might be related to stratification of the upper water mass linked to large annual amplitude of temperature with contrasting winter and summer conditions, high interannual-interdecadal variability, or taphonomic processes affecting some of the proxies. The average LGM SST in the Nordic Seas cannot at present be assessed with confidence. However, the existing evidence suggests that highly variable sea-surface conditions and at least occasional advection of North Atlantic waters may have characterised the glacial Nordic Seas. (c) 2006 Elsevier Ltd. All rights reserved.