South Atlantic Subtropical Gyre Late Twentieth Century Changes

This study builds upon existing research suggesting recent changes in the circulation of global subtropical gyres with respect to the South Atlantic Ocean using simulation results from the ocean component of the Community Earth System Model version 1the Parallel Ocean Program version 2. The results point to an intensification of the total anticyclonic circulation of the subtropical gyre and a southward displacement of the system, as revealed by the wind stress curl, sea surface height, and barotropic stream function fields. Increased values of these variables were found within the dynamical limits of the South Atlantic Subtropical Gyre (SASG), while their basin-scale structure seemed to be concurrently drifting poleward. The southern branch of the South Equatorial Current (sSEC) marks the northern boundary of the SASG. When reaching the South American coast, it bifurcates into the North Brazil Undercurrent to the north and the Brazil Current to the south. The sSEC bifurcation latitude (SBL) dictates the partition between the waters flowing poleward to recirculate within the SASG and those flowing toward the equatorial region and the Northern Hemisphere. A southward migration of the SBL at a rate of -0.11 degrees 0.03 degrees/year was observed, associated with a substantial increase in the equatorward advection of waters within the sSEC-SBL-North Brazil Undercurrent system. Plain Language Summary Subtropical gyres are wind-driven ocean circulation features. They provide a major pathway for water in the subtropics to be transported to the equator and high latitudes, which is believed to play a key role in modulating the world's climate system. This study uses model simulation data which covers the period from the late 20th to the early 21st century to show important changes taking place in the circulation of the subtropical gyre in the South Atlantic Ocean. Its counterclockwise circulation is shown to be accelerating and shifting to the south, toward the pole. These changes seem to be further related to an intensification of the northward flowing branch of the so-called global ocean conveyor belta larger-scale circulation in which the South Atlantic Subtropical Gyre is inserted. These results represent strong evidence of climate change-induced circulation patterns which are likely to have important consequences on the global climate system as well as regional climates and ecosystems.