The Meridional Overturning Circulation plays an important role to the global heat and salinity budgets and is also believed to be linked with climate parameters such as rainfall and surface air temperature in the northern hemisphere. There is increasing evidence that the South Atlantic may be playing a crucial role to the MOC variability. However, compared to the North the South Atlantic is poorly sampled. Therefore, in an attempt to understand the variability of the upper branch of the Meridional Overturning Circulation in the South Atlantic, a three dimensional absolute velocity product is constructed using sea surface height measurements from satellite altimetry, observations from Argo floats, and wind fields. These velocity fields along with the hydrographic profiles are then used to estimate meridional volume and heat transport at several latitudes in the South Atlantic. To study the meridional coherence of the Meridional Overturning Circulation in more detail, three dimensional velocity fields are derived for the North Atlantic following the same approach as in the South Atlantic. These velocity fields are used to estimate the meridional volume and heat transports at several latitudes in the subtropical North Atlantic.

(a) Meridional volume transport in the upper 400m in the South Atlantic using Argo observations and satellite altimetry, the dotted lines mark the sections across 20°S, 25°S, 30°S, and 35°S where the strength of upper branch of the Meridional Overturning Circulation is estimated.

(b) Time series of the strength of the Meridional Overturning Circulation (MOC in Sv = 10⁶ m³ s^-1) at 35°S.