Sea ice in the northern North Atlantic through the Holocene: Evidence from ice cores and marine sediment records

Sea ice plays a pivotal role in Earth's climate and its past reconstruction is crucial to investigate the connections and feedbacks with the other components of the climate system. Among the available archives that store information of past sea ice are marine and ice cores. Recent studies on the IP 25 biomarker extracted from marine sediments has shown great skill to infer past changes of Arctic sea ice. In ice matrixes, sodium, bromine and iodine have shown potential to store the fingerprint of sea ice presence. The development of an unambiguous sea ice proxy from ice cores, however, has proven to be a challenging task especially in the Arctic realm. In this work we analyze the sodium, bromine and iodine records in the RECAP ice core, coastal eastern Greenland, to investigate the sea ice variability in the northern North Atlantic Ocean through the last 11,000 years of the current interglacial, i.e. the Holocene. We compare the RECAP records with marine sea ice proxy records available from the northern North Atlantic. We suggest that RECAP sodium concentrations can be associated with variability of sea ice extent, while the bromine-to-sodium ratios and iodine are associated respectively with seasonal sea ice and bioproductivity from open ocean and fresh sea ice surfaces. According to our interpretation, we find that sea ice was at its lowest extent and seasonal in nature during the early Holocene in all regions of the North Atlantic. Increasing sea ice signals are seen from ca. 8-9 ka b2k, in line with long-term Holocene cooling. The increasing sea ice trend appears uninterrupted in the Fram Strait and North Iceland while reaching a maximum ca. 5 ka b2k in the East Greenland region. Sea ice modifications during the last 5000 years display great variability in East Greenland with intermediate conditions between the early and mid Holocene, possibly associated with local fjord dynamics. The last sea ice maximum was reached across all regions 1000 years b2k. (C) 2021 Elsevier Ltd. All rights reserved.

Automated summary

Sea ice is a key component of Earth's climate, and past reconstructions are essential for understanding its connections with other parts of the climate system. Recent research has shown that biomarkers from marine sediments and elements in ice cores can be used to infer past changes in Arctic sea ice. Analysis of sodium, bromine, and iodine in ice cores from coastal eastern Greenland can provide insights into sea ice variability in the northern North Atlantic over the past 11,000 years. The data suggests that sea ice extent was lowest and seasonal in nature during the early Holocene, followed by increasing sea ice signals from around 8-9 thousand years ago in line with long-term cooling trends.