Instantaneous Antarctic ice sheet mass loss driven by thinning ice shelves

Abstract

Recent observations show that the rate at which the Antarctic ice sheet (AIS) is contributing to sea level rise is increasing. Increases in ice-ocean heat exchange have the potential to induce substantial mass loss through the melting of its ice shelves. Lack of data and limitations in modeling, however, has made it challenging to quantify the importance of ocean-induced changes in ice shelf thickness as a driver for ongoing mass loss. Here, we use a numerical ice sheet model in combination with satellite observations of ice shelf thinning from 1994 to 2017 to quantify instantaneous changes in ice flow across all AIS grounding lines, resulting from changes in ice shelf buttressing alone. Our process-based predictions are in good agreement with observed spatial patterns of ice loss, providing support for the notion that a significant portion of the current ice loss of the AIS is ocean driven and caused by a reduction in ice shelf buttressing.Plain Language Summary The Antarctic ice sheet is currently losing mass, but the causes for the mass loss remain unclear. It has been suggested that the reduction in the thickness of the floating ice shelves that surround the ice sheet, for example, due to ocean warming or changes in ocean circulation, may be responsible for some of the observed ice loss. However, this hypothesis has remained untested. Here, we use a state-of-the art numerical ice flow model to calculate the direct mass loss due to observed changes in ice shelves between 1994 and 2017. We find that the magnitude and spatial variability of modelled changes of inland ice are in good agreement with observations, suggesting that a substantial portion of the recent ice loss from the grounded Antarctic ice sheet has been driven by changes in its thinning ice shelves. The process we consider (ice shelf buttressing) relates to changes in forces within the ice alone and is therefore effectively instantaneous (i.e., only limited by the speed of stress transition within the ice). Besides providing a possible explanation for a large part of the ongoing mass loss, this finding also shows that we are not protected against the impact of the Antarctic ice sheet on global sea levels by a long response time.

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

“…6 A-G illustrates the sequence of events that take place as the ice sheet evolves. First, loss of the Filchner-Ronne Ice Shelf in the Weddell Sea triggers a nonlinear response, removing the buttressing force that stabilizes grounded ice across large parts of the WSE and the EAIS (most notably the Recovery Basin) (55). The loss of back-stress allows for an acceleration of grounded ice and a rapid but short-lived thinning episode (32).…”

Results of the third Marine Ice Sheet Model Intercomparison Project (MISMIP+)

“…It did not, however, feature strong buttressing of the kind that is important in Antarctic ice shelf and ice stream systems. Recent real world cases include applications to Pine Island Glacier (Joughin et al, 2019) and Thwaites Glacier (Yu et al, 2018) in Western Antarctica, and in Antarctica as a whole (Gudmundsson et al, 2019;Martin et al, 2019).…”

32-year record-high surface melt in 2019/2020 on north George VI Ice Shelf, Antarctic Peninsula

“…atmosphere and bed conditions (Scambos et al, 2000;Bell et al, 2018;Tuckett et al 2019;Smith et al, 2020). An important part of this system are ice shelves, which have a total area of ~120,000 km 2 around the AP (Siegert et al, 2019), and act to buttress the inland ice from flowing into the ocean (Scambos et al 2004;De Rydt et al, 2015;Fürst et al, 2016;Gudmundsson et al, 2019).…”