Ocean circulation shifts and sea-ice decline in the North Atlantic-Arctic sector during the Last Interglacial

The Last Interglacial (127,000–116,000 years before present) is characterized by higher Arctic surface temperatures relative to the pre-industrial era. During this period, the Arctic experienced significant summer sea-ice reduction, with some studies suggesting the possibility of an ice-free Arctic Ocean at the end of summers. These changes in sea-ice cover were primarily driven by increased summer solar insolation caused by orbital configuration at that time, but they may also have been influenced by shifts in oceanic conditions. Paleoceanographic studies generally assume modern-like circulation patterns when interpreting proxy data. However, the stability of oceanic circulation under Last Interglacial forcing and its potential impact on sea-ice loss remain poorly understood.

Using simulations from the last Coupled Model Intercomparison Project (CMIP6/PMIP4), we analysed differences in surface ocean circulation between the Last Interglacial and pre-industrial periods, and their effect on annual sea-ice variations. Our results indicate an anomalous cyclonic circulation over Greenland and the surrounding seas, which leads to intensified Baffin and Labrador Currents west of Greenland and a weakened East Greenland Current. These changes affect sea-ice drift and water transports outside the Arctic Basin. Furthermore, models generally simulate a strengthening of the North Atlantic subpolar gyre during the Last Interglacial, associated with increased Atlantic inflows south of Greenland and towards the Nordic Seas. Despite these changes, we found no consistent evidence of "Atlantification" of the Arctic during the Last Interglacial. This contrasts with future CO2 emission scenarios, where similar reductions in annual sea-ice volume are accompanied by Atlantification.