| Summary: | Joint Assembly IAPSO-AIAMA-IAGA , Good Hope for Earth Sciences, 27 August - 1 September 2017, Cape Town, South Africa The South Atlantic is the only basin with net heat transfer from the extratropics to the tropics. Despite its crucial role in the returning limb of the Atlantic meridional overturning circulation, the subtropical to tropical paths are yet poorly understood. Here we study these pathways using a climatological output of the GLORYS 2V4 simulation (0.25º resolution). Our goal is to understand what mechanisms connect the subtropical and tropical gyres, inducing predominant northward transfer. For this purpose we examine the proportion of subtropical-tropical transfer that occurs in the middle of the ocean as opposed to the western boundary, and the paths of propagation as a function of depth, density and location. We pay special attention to assess the spatial and temporal windows (starting at the time and location of the deepest surface mixed layer with positive wind-stress curl) that would allow the exchange between the subtropical and tropical gyres through obduction, as well as to the possibility of annual-mean epipycnal pumping (arising from the positive net correlation between latitudinal velocity anomalies and layer thickness). For our calculations we use the horizontal and vertical velocities for the annual-mean, monthly-mean and climatological flow fields. We show these velocity fields at different depth and density levels and along vertical latitudinal sections, and present the Eulerian and Lagrangian streamlines, the latter calculated through the forward and backward tracking of water particles starting at different latitudinal and meridional sections. We find that most of the transfer occurs in the western boundary through the North Brazil Undercurrent, which corresponds to water parcels along density layers that are obducted in the western half of the subtropical gyre. These waters come from the South Equatorial Current for upper thermocline waters, and from further south for the ...
|
|---|