Oceanographic observations at the shelf break of the Amundsen Sea, Antarctica

The glaciers draining into the Amundsen Sea Embayment are rapidly losing mass, making a significant contribution to current sea level rise. Studies of Pine Island Glacier (PIG) in this region indicate that the mass loss is associated with rapid melting of its floating ice shelf into relatively warm Circumpolar Deep Water (CDW) that is able to penetrate all the way to its grounding line, and that recent intensification of the mass loss is associated with higher melt rates and stronger sub-ice-shelf circulation. CDW is sourced from within the Antarctic Circumpolar Current situated well north of the glacial ice fronts. To be able to access the Amundsen Sea glaciers, CDW must first cross the continental shelf break where the deep ocean meets the shallower waters of the continental shelf. Here we present data that shows how CDW can cross from one regime to the other. On-shelf flow of CDW is enhanced where a subsea trough bisects the shelf edge. A previously unreported undercurrent is observed flowing eastwards along the shelf edge and when this current encounters the trough mouth it circulates southwards into the trough and towards the glaciers. Upwelling associated with this trough circulation appears to allow Lower CDW onto the shelf that would otherwise be blocked by the topography. These observations concur with the results of a theoretical modelling study of circulation in a similar topographic setting and also with the results of a regional ocean/ice modelling study of the Amundsen Sea specifically

Oceanic heat transport onto the Amundsen Sea shelf through a submarine glacial trough

Glaciers which drain the West Antarctic Ice Sheet (WAIS) into the Amundsen Sea are accelerating and thinning rapidly. These observations have been attributed to the regional oceanography whereby heat contained within Circumpolar Deep Water (CDW) drives the basal melting of floating glaciers. On the basis of new data we calculate that 2.8 terra-Watts (1012) of oceanic heat flow onto the continental shelf and toward the glaciers via a submarine glacial trough. This is enough to account for most of the basal melting in the entire region suggesting the ocean is supplying an excess of heat toward the Antarctic continent