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

• Main Authors: Walker, D. P., Jenkins, A., Brandon, M., Assmann, K., Shoosmith, D.
• Format: Conference Object
• Language: unknown
• Published: 2012
• Subjects: Amundsen Sea; Antarctic; West Antarctic Ice Sheet; Antarc*; Antarctica; Ice Sheet
• Online Access: https://oro.open.ac.uk/36287/; https://oro.open.ac.uk/36287/1/EGU2012-11070.pdf; http://meetingorganizer.copernicus.org/EGU2012/EGU2012-11070.pdf

The part of the West Antarctic Ice Sheet that drains into the Amundsen Sea is currently thinning at such a rate that it contributes nearly 10% of the observed rise in global mean sea level. Acceleration of the outlet glaciers appears to be caused by thinning at their downstream ends, where the ice goes afloat, indicating that the changes are probably being forced from the ocean. Observations made since the mid-1990s on the Amundsen Sea continental shelf have revealed that the deep troughs, carved by previous glacial advances, are flooded by almost unmodified Circumpolar Deep Water (CDW) with temperatures around 3-4°C above the freezing point, and that this water mass drives rapid melting of the floating ice. Here we report observations of water properties and currents made in the region where one of those troughs reaches the continental shelf edge. We estimate the absolute circulation within the trough from a combination of detided Acoustic Doppler Current Profiler data and geostrophic shear derived from Conductivity-Temperature-Depth sections. The shelf edge region is characterised by a landward deepening of the pycnocline separating CDW from the overlying colder and fresher surface waters. This feature, the so-called Antarctic Slope Front (ASF), is almost circumpolar in extent, and is typically a full-depth feature, the pycnocline intersecting the seabed over the upper continental slope. However, the ASF is weaker in the Amundsen Sea, where it is rarely a full-depth feature. Geostrophic shear associated with the ASF leads to a weakening of the associated westward current with depth, and an eastward undercurrent of varying strength has been reported at other locations. At the time of our Amundsen Sea observations the westward surface flow was weak, giving rise to a strong eastward undercurrent flowing along the continental shelf edge and upper slope. At the upstream (western) side of the trough the undercurrent turns south, driving a net on-shelf flow of CDW in the western part of the trough, and leaving a ...