Meeting Documents

Icebergs, Right Ahead?: Implications for Future Ice Shelf-Ocean Interactions in the Changing Icescape Environment at West Ice Shelf, East Antarctica

Abstract

West Ice Shelf (WIS) last calved a tabular iceberg, D-15, in 1992. It immediately reattached itself to the WIS via fast ice, essentially serving as a proxy ice tongue. It was stable for ~25 years as one of East Antarctica's largest areas of floating ice. Suddenly in late 2015, satellite imagery showed that D-15 had split in two; it has continued to undergo a slow-motion collapse since then.

We find that glacier flow across the WIS grounding line experienced an ocean warming-induced increase prior to 2012 that significantly slowed in 2014-2015, after which it resumed its increasing trend 2017-present. We deduce that faster flow velocity of the WIS prior to 2014 impinged the ice shelf onto an uncharted seamount, at least 9 km wide and likely less than 200 m from the ocean surface. We monitor the ongoing breakup using several datasets. First, the magnitude of the collision and iceberg splitting is investigated using acoustic stations around the Pacific Ocean as far north as the equator. Second, we have derived ice thickness changes using both ICESat and ICESat-2 laser altimetry, complemented by visible and infrared satellite imagery, enabling monitoring of changes in that shape over time, and velocity records. We compare this time series to records of sea ice concentration and local hydrography from the MEOP and Argo programs and ECCO2 reconstructions to deduce the influence of ocean heat variability on changes in upstream flow and stress balance.

We find the main driver behind the pre-2014 speedup was likely driven by wind-induced warm water upwelling in the region. Since then, variability in local winds and coastal currents have driven lower than average sea ice conditions and heightened polynya activity, driving water column mixing and cooling in recent years. When D-15 eventually leaves the coast, the icescape will change significantly, and likely affect access to the WIS cavity by warm offshore waters. Overall, we present the effects of the changing WIS icescape on future ice shelf melt, and contrast this scenario against areas undergoing similar changes following the removal of long-grounded icebergs and associated landfast ice, at Filchner Ice Shelf and Wilkins Ice Shelf in West Antarctica, to characterize the impacts of grounded icebergs on ice shelf-ocean interactions more generally.