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.Plain Language Summary The Southern Hemisphere super gyre (SHSG) is an interconnected circulation system of the southern subtropical gyres. It sweeps out of the Tasman Sea, transports water westward, and feeds the upper limb of the Atlantic thermohaline circulation through the Tasman and Agulhas leakages. The SHSG absorbs substantial quantities of atmospheric gases, such as oxygen and CO 2 , thus directly contributing to climate change. In this study, we analyze remotely sensed altimeter measurements, in situ observations, and outputs of an ocean general circulation model. The results reveal a two-decade-long spin-up of the SHSG. The inter-ocean exchange through the Tasman and Agulhas leakages shows an increasing trend during the period 1993-2016. This long-term trend may be attributed to changes in westerly winds associated with an increasing southern annular mode.

Variability of the Sub‐Antarctic Mode Water Subduction Rate During the Argo Period

“…Nearly 70% of the observed increase in the total SAMW volume between 2005 and 2015 can be accounted for by the increasing SAMW subduction rates. Enhanced westerly winds associated with an increasing SAM directly contribute to the deepening of the MLDs, the strengthening of the subtropical gyres (Qu et al, 2019;Ridgway & Dunn, 2007;Roemmich, 2007), the increasing of the SAMW subduction rates, and eventually the warming of the subsurface layers in the extratropical Southern Hemisphere ocean. downloaded at http://apdrc.soest.hawaii.edu/ website, and the NCEP Reanalysis wind product was downloaded at https://www.esrl.noaa.gov/psd/data/gridded/data.ncep.reanalysis.surfaceflux.html/ website.…”

Ocean Heat Storage in Response to Changing Ocean Circulation Processes

“…Similar studies that investigated changes in the subtropical gyres under climate change also emphasized changes in WBCs. All WBCs (except the Gulf Stream) are expected to intensify and to shift poleward (Yang et al 2016(Yang et al , 2020Qu et al 2019), with a larger warming trend over the WBCs than globally (Wu et al 2012). G. suggested that an increase in the stratification (Luo et al 2018) strengthens the barrier between the upper and lower circulation due to the baroclinic nature of the gyres, and thereby results in acceleration at near surface and slowdown in the lower thermocline.…”

Three-ocean interactions and climate variability: a review and perspective

“…Measurements and monitoring of the TL are difficult because the TL involves oceanic eddies and filaments. A recent study showed that the TL may carry as much as 10 Sv of Pacific water to the Indian Ocean (Qu et al 2019). TL variations on various timescales and their relationships with climate variability need to be studied.…”