Award: OPP-1644118

One of the most pressing issues in preparing for future climate change is understanding how ice sheets in Greenland and Antarctica will contribute to sea level rise through the melting of continental ice. We currently monitor large ice sheets using a variety of satellite-based methods and the scientific community has developed elaborate models of ice sheet response to ocean and atmospheric warming. All meltwater from continently ice ends up in the ocean, suggesting additional avenues for the detection of ice sheet change. With this project we developed a methodology to detect freshwater input into the Southern Ocean while also making an attribution to its source, whether it be precipitation over the ocean, melting of sea ice, or melting of glacial ice. The method is relatively straightforward and involves collecting seawater samples along with in situ temperature and salinity data. Seawater samples are analyzed for their stable oxygen isotopic composition. Since polar ice sheets are composed of frozen freshwater with a very negative stable isotopic signature, we can detect the glacial meltwater signal in the ocean, even if the signal is diluted by mixing with "normal" seawater or freshwater derived from other sources. We focused our efforts initially on Pine Island Bay in West Antarctica, the focus of a large number of ongoing research projects because of the expected large contribution of glacial melt from this area over the next several decades. By making about 2,000 new measurements of sweater oxygen isotopic composition and combining these values with previously analyzed samples, we have shown that the inventory of glacial meltwater in Pine Island Bay has indeed increased over the past 25 years but not as much as expected. Our data suggests that much of the ice sheet loss in Pine Island Bay occurs through glacial calving wherein iceberg transport delivers freshwater further offshore than the coastal sea where calving occurs. Measurements of coastal water masses derived from further offshore show recent increases in glacial meltwater concentrations, consistent with an overall increased flux of continental ice meltwater into the Southern Ocean. Integration of these new isotopic data sets into models of Southern Ocean circulation will allow for more precise estimates of meltwater fluxes from continental ice to the sea. Last Modified: 09/16/2022 Submitted by: Robert B Dunbar