Seasonal variability of ocean circulation near the Dotson Ice Shelf

Abstract

The rapid thinning of ice shelves in West Antarctica has recently been established from remote satellite observations, especially in the Southeast Pacific where relatively warm deep water intrudes onto the continental shelf1,2. The heat that seawater supplies to ice shelves causes basal melting and transports the meltwater seaward. Lying south of the productive Amundsen Sea Polynya, the ~5800 km2 Dotson Ice Shelf has a high melt rate due to southward ocean heat transport along the Dotson-Getz Trough. To investigate the existence and effects of seasonal variability on the Dotson mass loss we deployed three bottom-moored instrument arrays near the ice shelf, obtaining vertical profiles of temperature, salinity, current speed and direction during 2014 and 2015. Deep water inflow velocities are highest near bottom along the eastern slope of the trough, and spread northward higher above its western slope after being freshened by ice shelf meltwater. The rate of warm water intrusion into the sub-Dotson cavity reached a maximum during summer, 60 % larger than a minimum during autumn and winter, and depended mainly on variability of the ocean wind stress curl. Meltwater outflows were strongest during autumn and weakest in spring, with velocities influenced by a zonal density gradient caused by the seasonal variability of its meltwater fraction, and melt export lagging heat import by 145 days. The thickness of warm deep water above the eastern slope changed from one year to the next resulting from variable Ekman upwelling along the trough. Southeasterlies wind on the eastern boundary of the polynya also differed between summers because of a shift in the meridional location of the Amundsen Sea Low.