Is the oceanic heat flux on the central Amundsen sea shelf caused by barotropic or baroclinic currents?

Abstract

The glaciers that drain the West Antarctic Ice Sheet into the Amundsen Sea are accelerating and experiencing increased basal melt of the floating ice shelves. Warm and salty deep water has been observed to flow southward in deep troughs leading from the shelf break to the inner shelf area where the glaciers terminate. It has been suggested that the melting induced by this warm water is responsible for the acceleration of the glaciers. Here we investigate the structure of the currents and the associated heat flow on the shelf using in-situ observations from 2008 to 2014 in Dotson Trough, the main channel in the western part of the Amundsen Sea shelf, together with output from a numerical model. The model is generally able to reproduce the observed velocities and temperatures in the trough, albeit with a thicker warm bottom layer. In the absence of measurements of sea surface height we define the barotropic component of the flow as the vertical average of the velocity. It is shown that the flow is dominated by warm barotropic inflows on the eastern side and colder and fresher barotropic outflows on the western side. The transport of heat appears to be primarily induced by this clockwise barotropic circulation in the trough, contrary to earlier studies emphasizing a bottom-intensified baroclinic inflow as the main contributor.