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Constraints on surface seawater oxygen isotope change between the Last Glacial Maximum and the Late Holocene


Estimates of the change in surface seawater δ18O (δ18Osw) between the Last Glacial Maximum (LGM) and Late Holocene (LH) are derived from homogenous data sets with rigorous age control, namely MARGO sea surface temperature (SST) estimates and oxygen isotopic ratios (δ18O) of planktonic foraminifers. Propagation of uncertainties associated with each proxy allows the identification of robust patterns of change in δ18Osw. Examination of these patterns on a regional scale highlights which changes in surface currents and hydrological cycle are consistent with both planktonic isotopic data and reconstructed SST. Positive local annual mean LGM-LH δ18Osw anomalies characterize the glacial tropical Indian Ocean, portions of the western and eastern margins of the North Pacific, the Iberian margin and the tropical North Atlantic, as well as the South African margin. Although reduced precipitation during the LGM with respect to the LH may have contributed to some extent to these local enrichments in surface seawater 18O, the largest positive anomalies appear to be related to changes in ocean circulation. Large local negative annual mean LGM-LH δ18Osw anomalies are found in the South Pacific and North Atlantic, reflecting the equatorward migration of surface temperature fronts during the LGM with respect to the LH. In the northern North Atlantic, a region characterized by large discrepancies between SST estimates based on different proxies, only SST estimates based on planktonic foraminifer counts yield annual mean LGM-LH δ18Osw anomalies consistent with a southward shift of the polar front at the LGM relative to the LH.

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