Upper Ocean Distribution of Glacial Meltwater in the Amundsen Sea, Antarctica

Pine Island Ice Shelf, in the Amundsen Sea, is losing mass due to increased heat transport by warm ocean water penetrating beneath the ice shelf and causing basal melt. Tracing this warm deep water and the resulting glacial meltwater can identify changes in melt rate and the regions most affected by the increased input of this freshwater. Here, optimum multiparameter analysis is used to deduce glacial meltwater fractions from independent water mass characteristics (standard hydrographic observations, (NG), and oxygen isotopes), collected during a ship‐based campaign in the eastern Amundsen Sea in February–March 2014. (NG) (neon, argon, krypton, and xenon) and oxygen isotopes are used to trace the glacial melt and meteoric water found in seawater, and we demonstrate how their signatures can be used to rectify the hydrographic trace of glacial meltwater, which provides a much higher‐resolution picture. The presence of glacial meltwater is shown to mask the Winter Water properties, resulting in differences between the water mass analyses of up to 4‐g/kg glacial meltwater content. This discrepancy can be accounted for by redefining the “pure” Winter Water endpoint in the hydrographic glacial meltwater calculation. The corrected glacial meltwater content values show a persistent signature between 150 and 400 m of the water column across all of the sample locations (up to 535 km from Pine Island Ice Shelf), with increased concentration toward the west along the coastline. It also shows, for the first time, the signature of glacial meltwater flowing off‐shelf in the eastern channel. Plain Language Summary Pine Island Ice Shelf in the Amundsen Sea, Antarctica, is melting due to warm ocean waters. The glacial meltwater that is produced is less salty and carries essential food for biological organisms, so where the glacial meltwater goes once it leaves the front of the ice shelf is important to understand: Less salt in the ocean at the surface makes it easier to form sea ice, and increased productivity from biological organisms can help draw carbon down into the ocean from the atmosphere. We use (NG) to identify where this glacial meltwater is, as the signature that the meltwater leaves in the gases is unique like a fingerprint. We use the noble gas meltwater signature to improve our identification of glacial meltwater using temperature, salinity, and dissolved oxygen (hydrographic observations), which are easier and cheaper to collect so cover a larger area. Using