The distribution of glacial meltwater in the Amundsen Sea, Antarctica, revealed by dissolved helium and neon

Abstract

The light noble gases, helium (He) and neon (Ne), dissolved in seawater, can be useful tracers f freshwater input from glacial melting because the dissolution of air bubbles trapped in glacial ice results in an approximately tenfold supersaturation. Using He nd Ne measurements, we determined, for the first time, the distribution of glacial meltwater (GMW) within the water columns of the Dotson Trough (DT) and in front of the Dotson and Getz Ice Shelves (DIS and GIS, respectively) in the western Amundsen Sea, ntarctica, in the austral summers of 2011 and 2012. The measured saturation anomalies of He and Ne (DHe and DNe) were in the range of 3-35% and 2-12%, respectively, indicating a significant presence of GMW. Throughout the DT, the highest values of DHe (21%) were observed at depths of 400-500 m, corresponding to the layer between the incoming warm Circumpolar Deep Water and the overlying Winter Water. The high DHe (and DNe) area extended outside of the shelf break, suggesting that GMW is transported more than 300 km offshore. The DHe was substantially higher in front of the DIS than the GIS, and the highest DHe (31%) was observed in the western part of the DIS, where concentrated outflow from the shelf to the offshore was observed. In 2012, the calculated GMW fraction in seawater based on excess He and Ne decreased by 30？40% compared with that in 2011 in both ice shelves, indicating strong temporal variability in glacial melting.