Variability of deep currents above the Mid-Atlantic Ridge in the South Atlantic

Abstract

Due to its geographical location, the South Atlantic subtropical gyre plays an important role in the Atlantic Meridional Overturning Circulation (AMOC), which controls the Earth’s climate by redistributing water masses, heat, and freshwater in the Atlantic. This thesis therefore studies the data collected by a mooring between April 2021 and April 2023, located on the eastern flank of the Mid-Atlantic Ridge (-21.631°N, -9.967°E), as part of the larger South Atlantic GAteway project. The water mass in which the mooring was placed (from 2351 m to the seafloor at 4407 m) was identified as the North Atlantic Deep Water (NADW). The currents measured in the upper part of the mooring, with a mean current weakly directed westward, were attributed to the influence of the South Equatorial Current, while the deeper currents, with a mean current directed eastward, were attributed to the transport of NADW over the Mid-Atlantic Ridge at these latitudes. Finally, sea level anomalies were compared with the variability in currents and temperature, and their synchronous variation along the depth was identified as disturbances from the westward propagation of long baroclinic Rossby waves.