Intense surface melting and firn saturation on the West Antarctic Ice Sheet during the 2019-2020 austral melt season mapped from space using satellite C-band radar scatterometry

Abstract:

Here, a 21-year climate record of enhanced-resolution C-band radar backscatter image time series generated from observations collected by radar scatterometers on two Earth-observing satellite missions that span nearly three decades (1992-present) is used to map surface and near-surface meltwater (< ~5 m) over the entire Antarctic Ice Sheet and infer extensive areas of subsurface firn saturation, or 'firn aquifers'. Several firn aquifer areas were recently identified using enhanced-resolution L-band brightness temperature image time series, and confirmed by 2018 and 2020 field expeditions to the Antarctic Peninsula. The most expansive of these areas is the Wilkins Ice Shelf. Results indicate that during the 2019-2020 austral melt season, the overall extent of seasonal surface melting on the Antarctic Ice Sheet was typical relative to the long-term satellite climate record; however, the intensity of surface melting on the West Antarctic Ice Sheet was exceptional, especially over the coastal regions, the peripheral ice shelves, and the surrounding ice-capped islands. All of the large ice shelves (i.e., Larsen C, Larsen D, Wilkins, George VI, Bach, and Stange) in the Antarctic Peninsula experienced meltwater durations that were exceptionally long. Several ice shelves along the northern Amundsen-Bellingshausen Sea coast that typically experience shorter meltwater durations (i.e., Venable, Abbott, Cosgrove and Pine Island) also experienced meltwater durations that were exceptionally long. High surface air temperatures and long microwave-derived meltwater durations have in general been linked to instability resulting from the potential to trigger hydrofracturing and catastrophic ice shelf collapse. However, we show that the longest microwave-derived meltwater durations are in areas of extensive subsurface firn saturation. Exceptional meltwater durations and subsurface firn saturation during the 2019-2020 austral melt season likely increased seasonal recharge rates and the total volume of meltwater stored within the perennial firn aquifer on the Wilkins Ice Shelf.as well as in other ice shelf areas.