SAGA10W Cruise: In Situ Monitoring of the Atlantic Meridional Overturning Circulation (AMOC)

Abstract

The South Atlantic Ocean is one of the central components of the climate system as it regulates the intensity of the Atlantic South Overturning Circulation (AMOC), which determines the amount of equatorward heat gained and transported to high latitudes (Garzoli and Matano, 2011). The main goal of the SAGA10W oceanographic cruise, carried out between March 7 and April 15 2021, was installing the appropriate equipment to perform a long time monitoring of the interior-ocean zonal flows linking the eastern and western South Atlantic basins. The equipment selected to perform the monitoring as well as the logistic of its installation was not trivial. It consisted of four PIES (Pressure Inverted Eco Sounder), and three 2000- m instrumented moorings installed along 10W on the spurs of the Mid-Atlantic Ridge between 34º20'S and 19º20'S. This vertical section takes place the verge of the subtropical and tropical gyres, in a region that has been recently identified as a pathway for both the starting and returning limbs of the AMOC: the South Atlantic Gateway (SAGA). To properly install the four PIES and three moorings it was absolutely necessary to perform a previous study of the bottom topography with enough resolution to decide the right location. Considering the period of planned monitoring (4 yrs), it was absolutely necessary to adequately prepare all submerged instrumentation. The detailed multibeam scanning of the bottom relief was performed around the points selected by GEBCO. The multibeam scanning covered a 20x20 nautical mile square and consisted of 5 meridional tracks 5 miles apart that allowed to obtain a real acoustic image of the bottom relief with a spatial resolution of 25 meters. Here, we present our experience in preparing the equipments, the cruise operations and the final setup of the entire SAGA array