Ocean-driven glacial melt estimation time series using salinity and oxygen isotopes in Pine Island Bay, West Antarctica

Andrew Nicholas Hennig, David Mucciarone and Robert B Dunbar, Stanford University, Stanford, CA, United States
Approximately 200,000km2 of West Antarctica are drained by the Pine Island Glacier via a floating terminus into Pine Island Bay. The mass balance in Western Antarctica is dominated by dynamic losses in the Amundsen Sea embayment, which have been accelerating in recent years. Mass losses in the Amundsen Sea sector are driven by oceanic melting, where warm subsurface waters come into contact with ice shelves. Satellite imagery approximates meltwater introduction into coastal seas based on elevation timeseries. Since glacial ice is freshwater, and extremely depleted in ẟ18O, these measurements can be used to calculate the fraction of glacial meltwater present in coastal seas adjacent to ice sheets. Here, we present a timeseries of direct meltwater measurements from Pine Island Bay in 2009 and 2019 using salinity and oxygen isotope data to directly infer meltwater fractions. On the continental shelf in the Amundsen Sea Embayment, there are three predominant water masses – Antarctic Surface Water, Modified Circumpolar Deep Water, and Winter Water – all of which show a freshening, and depletion of ẟ18O throughout the water column. Previous studies have identified 2009 as a peak in glacial melt in Pine Island Bay. These direct measurements indicate 60% greater meltwater presence than the previously identified peak in 2009. This substantial increase in meltwater content in 2019 compared to 2009 is indicative of a long-term trend of accelerating ocean-driven melt in addition to decadal variability.