CONICET | Buscador de Institutos y Recursos Humanos

The subtropical gyres are well-known features of the global oceans, forced by the large-scale wind stress curl patterns that form between the easterly Trade Winds and the subtropical westerlies. Sea surface height (SSH) and upper ocean heat storage in the South Atlantic subtropical gyre have recently been observed to increase associatedwith the spin-up of the gyre in response to a southward shift and intensification of the subtropical westerlies. Satellite and in situ observations are used to examine interannual to decadal variations of SSH, upper ocean heat content, and water mass properties within the gyre (between 35°S to 15°S) and within the sector just south of the gyre (between 55°S and 35°S). These variations are related to changes in the overlying winds, the gyre circulation,and the Atlantic Meridional Overturning Circulation (AMOC). Our results indicate that SSH and heat content in the South Atlantic have indeed been increasing over the past decades, but at disparate rates within the subtropical gyre (larger heat content trends) and within the region south of the gyre (larger SSH trends). Salinity driven (halosteric)SSH changes compensate for temperature driven (thermosteric) SSH changes in the gyre in the upper 700 m of the water column ? the surface waters in the gyre have become warmer and saltier on average since 2005. This compensation is less prevalent in the region south of the gyre because upper ocean warming has been paired with freshening. In both regions, water mass changes between 700 and 2000 m also influence SSH variations, whereweak warming/freshening are paired together in intermediate layers. Once the record-length trend is removed, the dominant mode of SSH variability is associated with interannual-to-decadal gyre spin-up/down. We will describe the dependence of this mode on the overlying winds and its influence upon the gyre circulation and AMOC variability.