Evidence of a sporadic northward flow of intermediate waters along the Western South Atlantic continental Slope at 34ºS: seasonal and interannual variability
Date:
This talk was presented within the PL08 Variability of the South Atlantic Circulation and its Inter-Basin Linkages and their role in the Climate System and Marine Ecosystems session: OSM2022.
ABSTRACT:
The Antarctic Intermediate Water (AAIW) in the western South Atlantic Ocean (SAO) plays a crucial role in the Atlantic Meridional Overturning Circulation (AMOC) as it contributes to compensate the export of North Atlantic Deep Water to other ocean basins. The low salinity (<34.3) and high oxygen concentration (>4.5 ml/l) AAIW is formed by subduction processes at the polar front. AAIW enters the SAO at intermediate depths along the Patagonian continental slope within the Malvinas Current (MC). Near 38ºS the MC encounters the southward flowing Brazil Current and both currents veer offshore. The main pathway of AAIW into the North Atlantic Ocean is through the subtropical gyre which, transports a salty variety of AAIW, after mixing with AAIW derived from the Indian Ocean in the Cape Basin. Previous studies suggest that a minor portion of the MC extends north of the Brazil-Malvinas Confluence (36ºS) along the continental slope of South America between 600 and 800 m depth. Based on oceanographic observations and numerical modeling, here we present new evidence of a narrow band of fresh AAIW extending northward past the Brazil Malvinas Confluence to about 34ºS. This flow is resembles the AAIW path originally proposed by Wüst (1395) based on the analysis of property distributions on the salinity minimum layer. We investigate the probability of occurrence of this phenomenon, the possible driving mechanisms and its seasonal and inter-annual variability. Our results indicate that, even though this flow is weak and has occasional intense pulses, it could be a direct pathway for AAIW from its origin in the subpolar region to the equator.