The water mass variability and southward shift of the Southern Hemisphere mid-depth supergyre

摘要

The Southern Hemisphere subtropical supergyre at intermediate depths connects all three ocean basins and plays a significant role in responding and conveying the climate-change-related variations in the global ocean.On the basis of the Simple Ocean Data Assimilation(SODA)ocean reanalysis,the thermohaline variability and southward shift of the mid-depth supergyre are demonstrated.The steric height of the subsurface relative to 1 500 m(400–1 500 m)from the SODA depicts exactly the flow patterns and variability of the oceanic supergyre.During 1958–2007 the water masses in the gyre interiors become cooler/fresher,with the significant exceptions of the Agulhas Current system and Agulhas leakage.The results also exhibit a pronounced strengthening of the inter-basin connection of the supergyre,and the strongest southward shift,by about 2.5 over the whole period,occurs in the central-south Pacific,which is associated with the changes in the basin-scale wind forcing.