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

Abstract

Abstract. 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 multi-proxy 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 (∼ 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.

Ocean‐Driven and Topography‐Controlled Nonlinear Glacier Retreat During the Holocene: Southwestern Ross Sea, Antarctica

“…A more southerly position of the Southern Hemisphere westerly wind belt drove an increased incursion of mCDW between 10.4 and 7.5 Kyr ago in the Amundsen Sea region (Hillenbrand et al, 2017). A similar inflow of mCDW could also have been possible in the Ross Sea at this time, as a large Ross Ice Shelf cavity had possibly not yet developed (Lowry et al, 2019), meaning that the production of sea ice and resulting HSSW was not yet occurring (Ashley et al, 2021) and thus not able to block mCDW (Jacobs et al, 1992). A freshening of the Southern Ocean during deglaciation could also have led to reduced Antarctic Bottom Water formation and then incursions of mCDW onto the Ross Sea continental shelf during the Early Holocene (Golledge et al, 2014).…”

Sensitivity of Holocene East Antarctic productivity to subdecadal variability set by sea ice

“…The mechanism for increased sea-ice duration at 4.5 ka is not a focus of this paper. It is noted around much of the Antarctic margin, being previously interpreted as a consequence of reduced local insolation forcing and enhanced ocean-ice shelf interactions 21 . Decreases in sand percent and MAR indicate an associated drop in current speed (Fig.…”

“…Age model. The age model was developed from 87 14 C dates from acid-insoluble bulk sedimentary organic carbon to constrain the ages of the sediment between ~11.4 ka BP and modern day 21 (Extended Data Fig. 1).…”

“…Bloom frequency was highest at ~8. 2 Green is biogenic silica MAR; brown is terrigenous 21 . d, Laminae frequency per 10 years smoothed in a five-point moving mean; the bold curve is an rlowess smoothing, using a 5% span of the data.…”

“…2). Comparison of the covarying siliciclastic (detrital) and biogenic MAR 21 (Fig. 3c) suggests that detrital and biogenic sediments are advected to the site together, under the influence of wind-driven currents and focused into the Adélie Basin by shelf bathymetry (Fig.…”