Ice shelf/ocean interactions under the Amery Ice Shelf: seasonal variability and its effect on marine ice formation

Marine ice is an important factor in ice shelf stability. An extensive marine ice layer is present under the Amery Ice Shelf (AIS), East Antarctica. This paper documents observations on the seasonal variability of the AIS–ocean interaction beneath its marine ice layer. We focus on data collected during 2002 through a borehole at AM01, 100 km from the ice shelf calving front, and use additional data from two other boreholes to complement the study. At AM01, the top ~20 m of the water column is super–cooled almost year–round, protecting the marine ice layer and promoting frazil ice formation. The mixed layer thickness varies from ~50 m in February to at least 160 m by June, as the water column cools and freshens. High Salinity Shelf Water (HSSW) abruptly arrives at AM01 in June–August as an eddy–like flow. We suggest that the flow characteristics are a result of baroclinic instabilities. In addition, the inflow of HSSW results in a steepening of the isopycnals that enhances the upwelling of Ice Shelf Water. This study documents, for the first time, a seasonal signal in the formation of marine ice under the AIS. Our results highlight the vulnerability of the marine ice layer to ocean variability with potential consequences for the overall ice shelf mass balance.