Influence of topography and winds on the distribution of water masses on the Antarctic Continental Shelf

Abstract

Central to improving our understanding of ocean temperature change on Antarctica’s continental shelf is a better understanding of how the ocean circulation drives the onshore flux of warm deep waters across the shelf break. This study uses a primitive equation ocean model to explore how the circulation regime and changes in surface stress influence the temperature structure on Antarctica’s shelf seas. As the shelf temperature changes are largely driven by ocean circulation changes, understanding these becomes our focus. A simple barotropic model is used to describe the linear theory of the difference between throughflow and gyres regimes, and their expected response to changes in forcing. This theory informs our understanding of the barotropic circulation response of the primitive equation model where a momentum budget confirms that over the simulated equilibrated timescales with surface forcing changes, the response is first-order linear. Consistent with previous findings, we find that climate change projection-like wind shifts (stronger westerlies that shift south) have a direct influence on Ekman processes across the shelf break and upwell warmer waters onto the shelf. We also find that the circulation regime (throughflow or gyre – determined by basin geometry), influences the mean shelf temperature and how susceptible the existing shelf temperatures are to changes in surface stress. While the throughflow regime can experience a complete transition in on-shelf temperatures when the transition between westerly and easterly winds shifts southward, we find relatively modest bottom intensified warming at the Ice Front in a gyre regime.