The breakup of iceberg D-15: Ice shelf-ocean interactions in a changing icescape environment at West Ice Shelf, East Antarctica
Authors: Walker Catherine C. , Neumann Thomas , Averbuch Gil , Zhang Weifeng 
Published: March 2024

West Ice Shelf (WIS) last calved a tabular iceberg, D-15, in 1992; at the time it was the largest East Antarctic calving event in decades. D-15 immediately reattached itself to the West Ice Shelf via fast ice, essentially serving as a ~19,000 square meter ice tongue. It was stable for ~25 years as one of East Antarctica&#8217;s largest areas of floating ice. Suddenly, in late 2015, satellite imagery showed that the large floating section had split in two; it has continued to undergo a slow-motion collapse since then.
Recently, changes in glacier terminus position (Miles et al., 2013; 2016) and glacier acceleration at Totten Glacier and Vincennes Bay (Greenbaum et al., 2015; Rintoul et al., 2016; Walker et al., 2018) have suggested that East Antarctica, long considered mostly stable, is starting to wake. With an ever-increasing satellite observational record, new investigations of dynamics in both time and space are now possible over sufficient scales.
We find that glacier flow across the WIS grounding line experienced an ocean warming-driven acceleration starting in 2012 that eventually slowed in 2015-2016 by 30%, after which it resumed its increasing trend 2017-present. We deduce that increasing flow velocity of the WIS in preceding years pushed the ice shelf into an uncharted seamount, at least 9 km wide and likely less than 200 m from the ocean surface. We monitor the ongoing breakup, now going on for >8 years, using several datasets. First, we have derived ice thickness changes, and importantly, basal topography of the floating ice sections using both ICESat and ICESat-2 laser altimetry complemented by visible and infrared satellite imagery, enabling monitoring of changes in that shape over time. We can compare this time series to records of ocean temperatures in the area to deduce the influence of ocean heat on past changes in flow and stress balance. In addition, we use recordings from the global hydroacoustic monitoring network maintained by the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) to characterize the breakup over time.
We find that the main driver behind the initial thinning of the iceberg itself was likely wind-induced warm water upwelling in the region. Variability in the winds and coastal currents have driven lower than average sea ice conditions, driving mixing and thus cooling in the years since. We demonstrate the relationship between atmospheric forcing, ocean change and glacier change using data collected by the Marine Mammals Exploring the Ocean Pole-to-Pole (MEOP) and Argo float programs, as well as ocean state estimates from ECCO2. Finally, we place this collapse event in context by comparing to similar ocean warming-induced icescape changes, including the removal of long-grounded icebergs, at Filchner Ice Shelf and Wilkins Ice Shelf in West Antarctica. We use these results to then characterize the implications for future ice-shelf ocean interactions at WIS once D-15 exits the area, likely within the decade. &#160;