Interannual variability in the subduction of the South Atlantic subtropical underwater

Abstract

The South Atlantic subtropical underwater (STUW) is a high-salinity water mass formed by subduction within the subtropical gyre. It is a major component of the subtropical cell and affects stratification in the downstream direction due to its high salinity characteristics. Understanding the interannual variability in STUW subduction is essential for quantifying the impact of subtropical variability on the tropical Atlantic. Using the output from the ocean state estimate of the Consortium for Estimating the Circulation and Climate of the Ocean (ECCO), this study investigates the interannual variability in STUW subduction from 1992 to 2016. We find that heat fluxes, wind stress, and wind stress curl cause interannual variability in the subduction rate. Heat fluxes over the subduction area modulate the sea surface buoyancy and regulate the mixed layer depth (MLD) during its deepening and shoaling phases. Additionally, the wind stress curl and zonal wind stress can modulate the size of the subduction area by regulating the probability of particles entrained into the mixed layer within 1 year of tracing. This analysis evaluates the influence of subtropical wind patterns on the South Atlantic subsurface high-salinity water mass, highlighting the impact of heat and wind on the interannual changes in the oceanic component of the hydrological cycle.

Influence of Salinity and Temperature Gradients on the Variability of the North Brazil Undercurrent

“…The NBUC carries a variety of water masses, including subtropical underwater (STUW; Liu et al, 2021), South Atlantic Central Water (SACW), Antarctic intermediate water (AAIW), and uCDW (Schott et al, 2005;Dossa et al, 2021). These water masses are characterized by extrema in temperature and salinity distributions.…”