Spin-Up of the Southern Hemisphere Super Gyre

Abstract

This study investigates the variability of the Southern Hemisphere super gyre (SHSG), using remotely sensed altimeter measurements, in situ Argo observations, and results from an ocean state estimate of the Consortium for Estimating the Circulation and Climate of the Ocean. Analyses of altimeter data show large trends of sea surface height, and their positive-negative contrast suggests a strengthening of subtropical gyres in all the three Southern Hemisphere oceans since 1993. Analyses of Argo data and the Estimating the Circulation and Climate of the Ocean estimate indicate that these dynamic signals of southern subtropical gyres extend to at least 2,000 m. The three southern subtropical gyres are interconnected through the Tasman and Agulhas leakages and vary consistently during the period 1993–2016. The Tasman and Agulhas leakages also show an increasing trend of inter-ocean water exchange with a typical increase of ~2 Sv (1 Sv = 10 6  m 3 /s) per decade, indicative of a two-decade-long spin-up of the SHSG. The strengthening and poleward shift of westerly winds are associated with an increasing southern annular mode, which affect the midlatitude and high-latitude Southern Hemisphere oceans and contribute to the spin-up of the SHSG.