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.

[1] The presence of warm Circumpolar Deep Water (CDW) intrusions on the Amundsen continental shelf has been linked to recent thinning of the outlet glaciers draining the West Antarctic ice sheet into the Amundsen Sea. Inflow of the CDW onto the shelf is thought to occur within a series of troughs that intersect the continental shelf break. We use observations between 1994 and 2011 and a numerical model to investigate the variability of CDW transport in a trough intersecting the shelf break at 113 W. The location of the main CDW inflow into the trough varies between its eastern flank and center, while the western part of the trough is filled by a recirculation that commonly entrains cooler water originating further south on the shelf. Thermocline depth decreases between the early and late 2000s with an indication that the depth of the 1994 thermocline was similar to the later years. Mooring results show that the CDW layer cools and thins in summer and thickens and warms in winter. In addition to a deeper thermocline in summer, we observe a stronger presence of Lower CDW in the bottom of the trough. Heat flux onto the shelf is controlled by current velocities rather than CDW temperature and the majority of the heat is carried onto the shelf by background flow rather than episodic events.

[1] 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 driven by 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 subice-shelf circulation. CDW is sourced from within the Antarctic Circumpolar Current (ACC) 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 moves along the continental slope and across the shelf break into the Amundsen Sea. On-shelf flow of CDW is enhanced where a subsea trough bisects the shelf edge. A previously unreported undercurrent is observed flowing eastward along the shelf edge and when this current encounters the trough mouth it circulates southward into the trough and toward 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 modeling study of circulation in a similar topographic setting and also with the results of a regional ocean/ice modeling study of the Amundsen Sea specifically.