A seasonally ice-free Arctic Ocean during the Last Interglacial

Abstract

The extent and seasonality of Arctic sea ice during the Last Interglacial (129,000 to 115,000 years before present) is poorly known. Sediment-based reconstructions have suggested extensive ice cover in summer, while climate model outputs indicate year-round conditions in the Arctic Ocean ranging from ice free to fully ice covered. Here we use microfossil records from across the central Arctic Ocean to show that sea-ice extent was substantially reduced and summers were probably ice free. The evidence comes from high abundances of the subpolar planktic foraminifera Turborotalita quinqueloba in five newly analysed cores. The northern occurrence of this species is incompatible with perennial sea ice, which would be associated with a thick, low-salinity surface water. Instead, T. quinqueloba’s ecological preference implies largely ice-free surface waters with seasonally elevated levels of primary productivity. In the modern ocean, this species thrives in the Fram Strait–Barents Sea ‘Arctic–Atlantic gateway’ region, implying that the necessary Atlantic Ocean-sourced water masses shoaled towards the surface during the Last Interglacial. This process reflects the ongoing Atlantification of the Arctic Ocean, currently restricted to the Eurasian Basin. Our results establish the Last Interglacial as a prime analogue for studying a seasonally ice-free Arctic Ocean, expected to occur this century.

Similarities and Differences in Arctic Sea‐Ice Loss During the Solar‐Forced Last Interglacial Warming (127 Kyr BP) and CO2‐Forced Future Warming

“…One such finding is that the AW inflow to the Arctic is warmer in the CO 2 ‐forced experiment than it may have been during the LIG. Planktonic species with a present‐day AW habitat, that are not found in Holocene sediments, exist in sediments from across the Central Arctic during past interglacials (Cronin et al., 2019; Nørgaard‐Pedersen et al., 2007; O’Regan et al., 2019; Vermassen et al., 2023). While discussions on age models persist, it can be debated whether these species may have inhabited the Arctic during the LIG alone, or were also present during previous interglacials.…”

“…While discussions on age models persist, it can be debated whether these species may have inhabited the Arctic during the LIG alone, or were also present during previous interglacials. However, the existing evidence suggests a higher degree of Atlantification during past interglacials compared to the Holocene (Vermassen et al., 2023). Currently, the Atlantification process is still largely limited to the eastern Eurasian Basin (Barents‐Kara‐Laptev Seas) in the high Arctic realm (Muilwijk et al., 2023; Polyakov et al., 2020).…”

“…To make progress in our understanding of sea‐ice processes, the focus has turned to the Last Interglacial (LIG; 129–116 Kyr before present; Otto‐Bliesner et al., 2017). While some proxies have been interpreted to point to perennial sea ice in the central Arctic (Cronin et al., 2010; Kremer et al., 2018; Stein et al., 2017), other studies suggest it was seasonally ice‐free during the LIG (Sime et al., 2023; Vermassen et al., 2023). This period, also sometimes called Marine Isotope Stage 5e (MIS 5e) or the Eemian, has been extensively analyzed through proxy reconstructions and has been the focus of targeted experiments of the Paleoclimate Modeling Intercomparison Project (PMIP4; Kageyama et al., 2018), in its contribution to CMIP6.…”

“…CMIP6 models support the assumption that the region from the western Canadian Arctic Archipelago to the northern coast of Greenland is the last area of the Arctic to lose its perennial ice cover (Notz & SIMIP Community, 2020;Wei et al, 2020). For lack of evidence, proxy reconstructions of sea ice often assume that if the region north of Greenland is ice-free in the past, then so is the rest of the Arctic (Detlef et al, 2023;Vermassen et al, 2023). However, it remains unclear whether this "last bastion," now commonly referred to as the "Last Ice Area" (Moore et al, 2019), assumption is robust during previous warm periods.…”

“…A comparison with an Arctic sea-ice proxy synthesis shows that models realistically capture annual sea-ice concentration in the North Atlantic region and Norwegian Sea during the LIG, but generally simulate too much ice close to the sea-ice edge in the Greenland Sea (Kageyama et al, 2021). Unfortunately, sites where semi-quantitative sea-ice reconstructions exist in the Central Arctic Ocean are scarce and often lack either the temporal resolution or age model confidence to unequivocally identify MIS 5e (Kageyama et al, 2021;Razmjooei et al, 2023;Vermassen et al, 2023).…”