Journal of Geophysical Research: Oceans

Subtropical cells and meridional overturning circulation pathways in the tropical Atlantic



[1] Pathways of subtropical cells (STCs) and the basin-wide meridional overturning circulation (MOC) are studied in the tropical Atlantic using a particle tracking algorithm and transports from a high-resolution ocean model. Here 16 Sv (=106 m3 s−1) of MOC water flows to the equator from the south, primarily in the North Brazil Current. The MOC water recirculates in the tropics and, after crossing the equator about half of it, stays along the western boundary and the other half loops in a cyclonic circulation northward to join the North Equatorial Current. The STC on the Southern Hemisphere has a strength of 4 Sv. The northern STC has a strength of 1.5 Sv; it is confined to the retroflection area close to the equator and it contains primarily MOC water. In total, 5.5 Sv of MOC water entrains into the mixed layer in the tropical Atlantic. Here 2 Sv of MOC water recirculates in the southern STC and 1.5 Sv in the northern STC. The STCs are weaker than suggested from observations, but the interior flows in the model compare well to observations. The heat transport divergence that is associated with warming of MOC water masses between 10°S and 10°N is 0.22 PW (=1015W). The fresh water transport divergence of MOC water masses in the tropical Atlantic is 0.16 Sv. It is concluded that the MOC can substantially affect the tropical circulation, but the tropical circulation itself can also affect MOC properties.