Sea ice variability from the penultimate glacial to the last interglacial in the Eastern Fram Strait

Abstract

The ongoing reduction of Arctic sea ice underscores the need to understand the drivers behind sea ice variability and associated ocean-climate impacts. The Last Interglacial, Marine Isotope (sub)Stage (MIS) 5e, and its transitions offer insights into sea ice variability during a period warmer than pre-industrial, and intervals of large climatic changes. This study examines a marine sediment core from the eastern Fram Strait, covering late MIS 6 to early MIS 5b (140–90 ka). We analysed organic biomarkers, including the PIP25 sea ice index and dinoflagellate cyst assemblages, complemented by stable oxygen isotopes, total organic carbon, and sediment physical properties (ice rafted debris, X-ray fluorescence, magnetic susceptibility). Our findings demonstrate a progression from extensive sea ice cover during late MIS 6 to a marginal ice zone during Termination II (T II) and open ocean conditions during MIS 5e, influenced by the Svalbard–Barents Sea Ice Sheet (SBIS) and warm Atlantic surface waters, superimposed on the gradual changes in Northern Hemisphere summer insolation. During late MIS 6, intermittent local polynyas formed by katabatic winds and Atlantic water intrusions temporarily disrupted the sea ice cover. During T II, the marginal ice zone environment, combined with organic matter-rich meltwater influx from the retreating SBIS may have enhanced the biological pump. MIS 5e exhibited a “two-step” warming with the strongest influence of Atlantic waters around ∼120 ka. Low to absent concentrations of biomarkers and dinoflagellate cysts immediately following MIS 5e complicate interpretations of sea ice and oceanic conditions during MIS 5d to MIS 5c, a crucial climatic interval characterised by periods with Northern Hemisphere summer insolation values comparable to today. These findings highlight the complexities of understanding Arctic sea ice responses to ocean-climate drivers and the need for further investigation into the unresolved MIS 5 proxy signals, important for improving our understanding of future sea ice decline and the associated ocean-climate impacts.