Reconstructed sub-polar sea ice shows a synchronous response to the abrupt climate warmings that occurred during the last glacial period.

This international effort has reconstructed, at high temporal resolution, the evolution of sea ice cover in the sub-polar region between Baffin Bay and the Labrador Sea, examining a series of abrupt climate oscillations that occurred between 36 and 44 thousand years ago. The work combines two sea ice records, on based on the analysis of marine salts (bromine and sodium) from an ice core drilled in northwest Greenland and the other based on the association of biomarkers in a marine sediment core extracted in the Labrador Sea. The results show that, in the sub-polar regions between the Baffin Bay and the Labrador Sea, the sea ice response to the repeated abrupt atmospheric warmings imprinted in the Greenland ice, was nearly synchronous, or occurred conservatively within a decade, shifting from a thick persistent multi-year ice cover to open ocean and seasonal ice conditions. This provides further evidence for the close relationship between climate warming and Arctic sea ice reduction. Climate cycles known as Dansgaard-Oeschger (D-O) events are characterized by an increase of up to +15 °C in atmospheric temperatures in Greenland in few decades, followed by a progressive cooling that can last up to 1-2 thousand years. Although some hypotheses link such abrupt oscillations to changing sea ice cover in the Arctic, dynamics and temporal linkage of the two processes were not entirely clear. From an applied environmental chemistry point of view, this study is a good example of the application of a fundamental chemical process (i.e. the auto-catalytic release of bromine species from sea ice saline substrates into the atmosphere, which eventually results in bromine-enriched snow deposited at the ice core site) to the reconstruction of past sea ice extent and the multi-year vs first-year sea ice fractions. Federico Scoto, Henrik Sadatzki, Niccolò Maffezzoli, Carlo Barbante, Alessandro Gagliardi, Cristiano Varin, Paul Vallelonga, Vasileos Gkinis, Alfonso Saiz-Lopez, Ruediger Stein, and Andrea Spolaor. Sea ice fluctuations in the Baffin Bay and the Labrador Sea during glacial abrupt climate changes. PNAS. DOI: https://doi.org/10.1073/pnas.2203468119