Circulation and Water Mass Variability in the South Atlantic Subtropical Gyre
Renellys C Perez, UM/CIMAS, Miami, FL, United States, Rym Msadek, GFDL/NOAA Princeton University, Princeton, NJ, United States, Silvia Lucia Garzoli, UM/CIMAS & NOAA/AOML, Miami, FL, United States, Ricardo P Matano, Oregon State Univ, Corvallis, OR, United States, Christopher S Meinen, Atlantic Oceanographic and Meteorological Laboratory, Physical Oceanography Division, Miami, FL, United States and Maria Paz Chidichimo, National Scientific and Technical Research Council (CONICET) / SHN, Buenos Aires, Argentina
Abstract:
Most observational and modeling efforts on the Atlantic meridional overturning circulation (AMOC) have been focused on the North Atlantic and the Southern Oceans, the main deep-water formation locations. There are comparatively fewer studies characterizing the water mass and circulation variability in the South Atlantic subtropical gyre, or how that variability impacts the AMOC in the South Atlantic, despite early work suggesting water mass changes in the South Atlantic are critical to AMOC stability. Here we use observations and high-resolution models to examine the interannual to decadal variability of sea level anomalies and water mass properties across the South Atlantic subtropical gyre. We evaluate meridional volume transports by the currents delineating the gyre’s zonal boundaries, such as the Brazil Current on the western boundary, and the Benguela Current on the eastern boundary. We highlight that waters transported by these currents, as well as the accumulated effect of Agulhas eddies on the eastern boundary, play an important role in the AMOC.
Observations analyzed in this study include time series measurements of water mass properties and velocities inferred from moorings along 34.5°S, gridded data sets in the South Atlantic such as Argo temperature and salinity profiles and satellite-derived products (e.g., sea level anomalies, currents, and winds). The robustness of these results is examined with output from the ECMWF ORAS4 ocean reanalysis and model results from a NOAA/GFDL ocean-only model simulation forced with CORE interannual forcing. The strongest mode of variability in the region is found to be characterized by sea level rise across the entire South Atlantic, while the second largest mode of variability is characterized by a decadal to multi-decadal South Atlantic subtropical gyre variability. These modes of variability impact water mass properties, create zonal density gradients, and impact the strength and structure of the boundary currents and AMOC across the basin. Our results hence stress the importance of better characterizing South Atlantic subtropical gyre variability in order to properly monitor the basin AMOC.
