Asynchronous Antarctic and Greenland ice-volume contributions to the last interglacial sea-level highstand

Abstract

The last interglacial (LIG;~130 to~118 thousand years ago, ka) was the last time global sea level rose well above the present level. Greenland Ice Sheet (GrIS) contributions were insufficient to explain the highstand, so that substantial Antarctic Ice Sheet (AIS) reduction is implied. However, the nature and drivers of GrIS and AIS reductions remain enigmatic, even though they may be critical for understanding future sea-level rise. Here we complement existing records with new data, and reveal that the LIG contained an AIS-derived highstand from~129.5 to~125 ka, a lowstand centred on 125-124 ka, and joint AIS + GrIS contributions from~123.5 to~118 ka. Moreover, a dual substructure within the first highstand suggests temporal variability in the AIS contributions. Implied rates of sea-level rise are high (up to several meters per century; m c −1 ), and lend credibility to high rates inferred by ice modelling under certain ice-shelf instability parameterisations.

Early Last Interglacial ocean warming drove substantial ice mass loss from Antarctica

“…The Patriot Hills record is consistent with basin-scale mass loss early in the LIG (15,32) as a consequence of regional ice dynamic changes and isostatically driven isolation of Horseshoe Valley from sustained ocean forcing. While some modeling studies have argued the loss of the Filchner-Ronne Ice Shelf does not display a strong marine ice sheet instability feedback (59) and that isostatically driven rebound may halt ice retreat (18), our results suggest otherwise.…”

“…This period experienced warmer polar temperatures and higher GMSL (+6 to 9 m, possibly up to 11 m) (4, 10-13) relative to present day, and was the most geographically widespread expression of high sea level during a previous warm period (4,10). LIG sea level cannot be fully explained by Greenland Ice Sheet melt (∼2 m) (8), ocean thermal expansion, and melting mountain glaciers (∼1 m) (4), implying substantial Antarctic mass loss (3,4,14,15). Half a century ago, John Mercer was the first to propose that the marine-based West Antarctic Ice Sheet (WAIS) is vulnerable to a warming atmosphere through loss of buttressing ice shelves and may have made a significant contribution to global sea level during the LIG (5)(6)(7).…”

The Sensitivity of the Antarctic Ice Sheet to a Changing Climate: Past, Present, and Future

“…DeConto and Pollard (2016) used the tuned MICI parameterisation in simulations of future AIS sea-level contributions under the IPCC RCP8.5 scenario, finding a global-mean sea-level contribution of 15.65 +/-2.00 m by 2500. The rates of sea-level rise corresponding to the DeConto and Pollard (2016) assessment are at the higher end of estimates based on natural climate forcing of sea level rise from paleoclimate data, which reveal an average of 1-2 m per century across past deglaciations, and 4-5 m per century during rapid pulses of sea level rise (Deschamps et al, 2012b;Grant et al, 2014;Rohling et al, 2013Rohling et al, , 2019. Observational evidence to support MICI is scarce, and is currently limited to one study of the maximum water depths and shapes of iceberg-keel ploughmarks eroded during the post-Last Glacial Maximum deglaciation on the West Antarctic continental shelf (Wise et al, 2017), and another based on glaciological evidence of rapid ice cliff calving in Greenland (Parizek et al, 2019).…”

Twenty first century changes in Antarctic and Southern Ocean surface climate in CMIP6

“…Changes in the Antarctic and Southern Ocean (SO) climate system are of global importance. The response of the Antarctic ice sheet in a warming world is a major component of projected 21st century changes in global sea level (DeConto and Pollard, ; Rohling et al ., ). The rate of anthropogenic heat and carbon uptake in the SO is a key influence on the rate of global warming not just in the future, but in the present day (Frölicher et al ., ; Hwang et al ., ; Bushinsky et al ., ; Gruber et al ., ).…”