Sea-ice variability in the subarctic North Pacific and adjacent Bering Sea during the past 25 ka: new insights from IP 2
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ORIGINAL ARTICLE
Sea-ice variability in the subarctic North Pacific and adjacent Bering Sea during the past 25 ka: new insights from IP25 and Uk′37 proxy records Marie Méheust1 · Ruediger Stein1,2 · Kirsten Fahl1 · Rainer Gersonde1 Received: 14 November 2017 / Accepted: 18 April 2018 © Springer-Verlag GmbH Germany, part of Springer Nature 2018
Abstract This study focusses on the last glacial–deglacial–Holocene spatial and temporal variability in sea-ice cover based on organic geochemical analyses of marine sediment cores from the subarctic Pacific and the Bering Sea. By means of the sea-ice proxy “IP25” and phytoplankton-derived biomarkers (specific sterols and alkenones), we reconstruct the spring sea-ice conditions, (summer) sea-surface temperature (SST) and primary productivity, respectively. The large variability of sea ice was explained by a combination of local and global factors, such as solar insolation, global climate anomalies and sea-level changes controlling the oceanographic circulation and water mass exchange between the subarctic Pacific and the Bering Sea. During the Last Glacial Maximum, extensive sea-ice cover prevailed over large part of the subarctic Pacific and the Bering Sea. The following deglaciation is characterized by a rapid sea-ice advance and retreat. During cold periods (Heinrich Stadial 1 and Younger Dryas) seasonal sea-ice cover generally coincided with low alkenone SSTs and low primary productivity. Conversely, during warmer intervals (Bølling/Allerød, Early Holocene) reduced sea-ice or ice-free conditions prevailed in the study area. At the northern Bering Sea continental shelf a late-Early/Mid Holocene shift to marginal sea-ice conditions is in line with the simultaneous wide-spread sea-ice recovery observed in the other Arctic marginal seas and is likely initiated by the lower Northern Hemisphere insolation and surface-water cooling. Keywords Last glacial to Holocene · Sea-ice cover · Biomarkers · North Pacific · Bering Sea
Introduction One of the key characteristics of the Arctic Ocean and its marginal seas—including the northern North Pacific and the Bering Sea—is the sea-ice cover with its strong seasonal variability. The Arctic sea ice is a critical and very sensitive component in the global climate system, that contributes to changes in the Earth’s albedo, the ecosystem and the Electronic supplementary material The online version of this article (https://doi.org/10.1007/s41063-018-0043-1) contains supplementary material, which is available to authorized users. * Ruediger Stein [email protected] 1
Department of Marine Geology, Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Am Alten Hafen 26, 27568 Bremerhaven, Germany
MARUM and Faculty of Geosciences, University of Bremen, P.O. Box 330440, 28334 Bremen, Germany
2
deep-water formation (e.g., [33, 51]). Over the last decades, this sea ice decreased dramatically in its extent and thickness [29, 86, 108, 114, 115], and the causes of these recent changes, i.e., natural versus anth
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