Why study SAMOC?
The South Atlantic Ocean is unique in its role as a nexus and melting pot for water-masses formed elsewhere and transiting between the far regions of the World Ocean. Its mean meridional circulation involves a deep, southward, flow of cold and salty North Atlantic Deep Water and, a compensating northward flow that is a mixture of warm and salty surface waters and cooler and fresher Antarctic Intermediate Waters. At a much greater depth, the lowest limb of the MOC is driven by formation of very salty and cold Antarctic Bottom Water near the Antarctic coast, and this limb of the MOC stretches throughout the complete South Atlantic, interacting with the North Atlantic Deep Water flow along the way before returning south. This complicated circulation pattern results in a significant equatorward oceanic heat flux, which is unlike any of the other ocean basins. Observations and models have shown that many of the components of the MOC in the South Atlantic are highly variable, with changes occurring on time scales ranging from a few days to many years. This variability is further complicated by the active transformation of these water masses as they pass through the South Atlantic. These changes occur across the entire basin, but are particularly intensified in regions of high mesoscale variability at the Brazil/Malvinas Confluence and at the Agulhas Retroflection. Observations show, for example, interannual variations in the sources that feed the Benguela Current, and hence in the upper ocean northward flow that eventually crosses the equator into the North Atlantic. It is this mounting evidence of the contribution of the South Atlantic to the global MOC system that has motivated broader study and international collaboration.
The main objectives of the SAMOC initiative are to measure the strength and variability of the MOC as well as the meridional heat and fresh-water transport in the South Atlantic, all of which are crucial to improving our understanding of climate system variability.