1257 / 2024-09-20 20:28:42

Mechanisms of cross-slope Circumpolar Deep Water intrusion in the Amundsen Sea, West Antarctica

Antarctic,Circumpolar Deep Water,ice shelf,Ocean modelling,slope front

The ice shelves in Amundsen Sea are experiencing a rapid melting phase, largely due to the intrusion of warm Circumpolar Deep Water (CDW) from off the continental shelf. At intrusion sites on the continental slope, the CDW, along with an eastward undercurrent, breaks the Taylor–Proudman theory, causing southward cross-isopycnal intrusion. To explore the mechanisms of the intrusion, we developed a coupled ocean-sea ice-ice shelf numerical model for the Ross Sea-Amundsen Sea system, reconstructing the circulations and simulating the CDW intrusion. The vorticity budget along the continental shelf break of Amundsen Sea 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. The intensity and vertical structure of the eastward undercurrent upstream significantly affect the density structure in the downstream intrusion area, promoting the JEBAR effect. The velocity of the eastward undercurrent is linked to the local wind field. We find that stronger eastward undercurrent speeds are associated with stronger westerly winds and weaker wind stress curl. Westerly winds can drive undercurrents via modifying the meridional sea surface altitude gradient, while wind stress curl reduces the undercurrent by weakening the strength of the continental slope front, which represents the wind field's own internal constraints on the undercurrent. Stronger negative wind stress curl in the Amundsen Sea could drive a stronger geostrophic component of Sverdrup transport under the Ekman layer, which may compress local isopycnals to alter the undercurrent on a seasonal timescale.