A Model Analysis of Circumpolar Deep Water Intrusions on the Continental Shelf Break in Amundsen Sea, Antarctica

Abstract

The ice shelves of the Amundsen Sea are in a phase of rapid melting with intruded Circumpolar Deep Water (CDW) from outside the continental shelf contributing most of the heat. Using a coupled sea ice—ice shelf—ocean general circulation model, the cross-shelf break heat flux and the mechanism of eastward undercurrent deflection are studied. Model results show higher cross-shelf break heat transfer during winter months regulated by both the barotropic and baroclinic geostrophic flow. The vorticity budget along the continental shelf break is examined using the depth-averaged vorticity budget equation based on the model's outputs. Results show that the advection of planetary vorticity (APV) and the joint effect of baroclinicity and relief (JEBAR) dominate the vorticity balance at the CDW intrusion sites on the shelf break, and the JEBAR effect is considered an effective indicator of CDW intrusion. The CDW intrusion is mainly regulated by the southward deflection of the undercurrent on the Amundsen Sea slope. Pre-deflection, the undercurrent's core lies on the southern edge of the shelf break, enabling it to modulate downstream density transport through its vertical distribution variations. Concurrent increases in undercurrent velocities and vertical extent are captured upstream of intrusion sites, supporting more CDW intrusions per unit time and altering the horizontal density gradient, thereby amplifying the JEBAR effect. Additionally, spectral analysis reveals a semiannual cycle in the JEBAR amplitude and heat flux across the Amundsen Sea slope.