Recent atmospheric precipitation contributes almost half of the freshwater input to the Amundsen Sea

Ice sheet mass loss, sea ice melt, and atmospheric precipitation increase stratification in the Antarctic shelf seas and the Southern Ocean, creating far-reaching impacts on overturning circulation and sea level rise. While mass loss by glacial melt may be the largest freshwater source, the contribution of recent precipitation is largely unknown. This study combined two water isotopes, tritium and oxygen-18, with salinity to trace each component of the freshwater budget as it spreads across the central Amundsen Sea shelf, revealing, for the first time, the contribution of atmospheric precipitation to freshwater in the coastal Antarctic seas. Precipitation in this region ranged from 1.3 to 21 g kg−1. Glacial melt ranged from 0.9 to 20 g kg−1, with the highest station-averaged values in front of the Dotson and Getz Ice Shelf outflows. Precipitation composed an average of 46% CI[37%,65%] of freshwater inputs, was most concentrated within the Amundsen Sea Polynya, and decreased offshelf. Our study brings new detail to the Antarctic hydrosphere by revealing that water isotope samples can determine precipitation, and by highlighting precipitation as an abundant freshwater input that may influence water-column stability and ocean circulation.