Meeting Documents

Controls on Circulation, Stratification, and Ventilation in Subpolar Gyres

Abstract

Subpolar gyres, found in the high latitudes of both the Northern and Southern Hemisphere, are important features of the global ocean – often serving as key regions for deep water formation and the uptake of climatologically relevant tracers like heat and carbon. However, unlike the predominantly wind-driven gyres of the subtropics, a first-order unifying framework for subpolar gyre circulation is not straightforward. This is because subpolar gyres, despite sharing the fundamental characteristic of cyclonic circulation, exhibit considerable complexity with markedly distinct configurations and surface forcings. Differences between subpolar gyres are found in their seasonal sea ice cover, continental boundaries and spatial extents, bathymetric influences, and styles and magnitudes of surface buoyancy fluxes. This complexity limits our fundamental intuition about these gyres and hampers efforts to predict future change in these critical regions.

Here we investigate the controlling factors on subpolar gyre circulation, stratification, and ventilation using the ECCOv4 ocean state estimate and an idealized ocean–sea ice model configuration. With ECCOv4, we constrain and analyze the characteristics of the world’s subpolar gyres through observations, making informative comparisons and gaining insight to processes supporting each gyre’s dynamics. We pair this with idealized simulations to explore the sensitivity of a generic high-latitude cyclonic gyre to wind stress, bathymetric configuration, sea ice conditions, and equatorward boundary type (e.g., a subtropical gyre or a circumpolar channel such as the Antarctic Circumpolar Current). By isolating key drivers behind gyre circulation, stratification, and ventilation, this work sheds light on the differences between the world’s subpolar gyres and allows us to speculate on their stability under future conditions.