Circumpolar Deep Waters undergoing modification within subpolar gyres

Circumpolar Deep Water (CDW) is a warm subsurface watermass that enhances basal melt rates of ice shelves in regions where it is able to access the coastline of Antarctica without losing much of its heat content. Subpolar gyres in the Weddell and Ross Seas and parts of East Antarctica are regions where CDW shoals close to the base of the pycnocline. In these regions, CDW is shallow enough to experience heightened rates of vertical mixing with the overlying waters leading to a loss of heat within the CDW layer.

Building on my previous research, where I investigated diapycnal mixing rates (watermass transformation rates) of CDW in a time-averaged context, I now aim to explore the variability of CDW transformation rates on seasonal and interannual timescales. My focus is on understanding the processes that control this variability, including the influences of gyres, winds, and buoyancy fluxes over the open Southern Ocean even before CDW reaches the continental shelf.

To achieve this, I intend to analyze the interannually forced run of ACCESS-OM2. I will begin by examining the covariability patterns between CDW transformation rates and those of gyres, winds, and buoyancy fluxes (specifically sea ice formation rates) in offshore Southern Ocean regions (south of ~60°S and off the continental shelf). Over interannual timescales, the response of gyres to winds may be influenced by the dominant modes of climate variability in the Southern Ocean, particularly the zonal waves responding to the IPO (Interdecadal Pacific Oscillation).

The study aims to address the following questions:

1. What impact do standing waves in Mean Sea Level Pressure (MSLP), such as the Weddell Sea Low and the Amundsen Sea Low, have on the expansion and contraction of subpolar gyres?
2. How does the variability in gyre intensity and spatial structure affect the extent of CDW transformation and the volume of CDW transformed?
3. How does sea ice respond to subpolar gyre variability, and how does this response affect surface buoyancy fluxes and CDW transformation rates?
4. How do the winds respond to the IPO and SAM?
   1. Do we observe enhanced mixing rates of CDW during periods of strengthened wind?
   2. Does the enhanced surface stratification during periods of positive SAM inhibit CDW mixing and transformation?