Mid-Holocene Antarctic sea-ice increase driven by marine ice sheet retreat

Over recent decades Antarctic sea-ice extent has increased, alongside widespread ice shelf thinning and freshening of waters along the Antarctic margin. In contrast, Earth system models generally simulate a decrease in sea ice. Circulation of water masses beneath large-cavity ice shelves is not included in current Earth System models and may be a driver of this phenomena. We examine a Holocene sediment core off East Antarctica that records the Neoglacial transition, the last major baseline shift of Antarctic sea ice, and part of a late-Holocene global cooling trend. We provide a multiproxy record of Holocene glacial meltwater input, sediment transport, and sea-ice variability. Our record, supported by high-resolution ocean modelling, shows that a rapid Antarctic sea-ice increase during the mid-Holocene (similar to 4.5 ka) occurred against a backdrop of increasing glacial meltwater input and gradual climate warming. We suggest that mid-Holocene ice shelf cavity expansion led to cooling of surface waters and sea-ice growth that slowed basal ice shelf melting. Incorporating this feedback mechanism into global climate models will be important for future projections of Antarctic changes.

Automated summary

In recent decades, Antarctic sea-ice extent has increased, contrary to the decrease simulated by Earth system models. The circulation of water masses beneath large-cavity ice shelves may be a key driver of this phenomenon. Analysis of a Holocene sediment core off East Antarctica reveals that mid-Holocene ice shelf cavity expansion led to cooling of surface waters and sea-ice growth, slowing down basal ice shelf melting. Incorporating this feedback mechanism into global climate models is crucial for future projections of Antarctic changes.