The Southern Ocean supergyre: a unifying dynamical framework identified by machine learning

Abstract

The Southern Ocean closes the global overturning circulation and is key to the regulation of carbon and heat, biological production, and sea level. However, the dynamics of the general circulation and upwelling pathways remain poorly understood. Here, a unifying framework is proposed invoking a semi-circumpolar `supergyre' south of the Antarctic circumpolar current: a massive series of ‘leaking’ sub-gyres spanning the Weddell and Ross seas that are connected and maintained via rough topography that acts as scaffolding. The supergyre framework challenges the conventional view of having separate circulation structures in the Weddell and Ross seas and suggests a limited utility for climate applications of idealized models and conventional zonal averaged frameworks. Machine learning was used to reveal areas of coherent driving forces within a vorticity-based analysis. Predictions from the supergyre framework are supported by available observations and could aid observational and modelling efforts of the climatically key region undergoing rapid change.

A Scale‐Dependent Analysis of the Barotropic Vorticity Budget in a Global Ocean Simulation

“…As a result, a domain‐averaged vorticity budget cannot pick up fields that have large magnitudes but with spatially alternating signs. Furthermore, the relative magnitudes of domain‐averaged vorticity budget terms can be sensitive to the choice of domain boundaries (Sonnewald et al., 2023; Stewart et al., 2021). The resultant domain‐averaged vorticity balance cannot represent the true nature of vorticity dynamics and can lead to incomplete or incorrect interpretations.…”

“…Global analyses from ocean state estimates and in situ observations also show that the Sverdrup balance holds only in the tropics and subtropics (Gray & Riser, 2014; Thomas et al., 2014; Wunsch, 2011). These differences in the interpretation of regional vorticity balances are partly due to the choice of regional boundaries for vorticity budget integration (Sonnewald et al., 2023). For example, bottom pressure torque vanishes when integrated over any area enclosed by an isobath, and the planetary vorticity advection appears to be controlled by wind stress and bottom friction (Kiss, 2004; Stewart et al., 2021).…”