An observations and model‐based analysis of meridional transports in the South Atlantic

A three‐dimensional velocity field constructed from Argo observations and sea surface heights (called Argo and SSH, hereinafter) is used to estimate meridional overturning volume transport and meridional heat transport (MHT) across 20°S, 25°S, 30°S, and 35°S for the years 2000–2014 in the South Atlantic. Volume transport in the upper branch of Meridional Overturning Circulation (MOC) and MHT from the observations are consistent with the previous observations, but are higher than the estimates derived from three data assimilative ocean models, at some of the latitudes. Both the observations and models show strong correlations between the strength of MOC and MHT at all the latitudes. The corresponding change in MHT for 1 Sv change of MOC strength, in the observations, increases from 0.046 PW in 25°S, 30°S, and 35°S to 0.056 PW across 20°S. A comparison of model‐based transports at 35°S at the boundaries and in the interior with those from Argo and SSH shows significant differences between them with respect to the contributions in the three segments of the section. In addition, the contributions also vary greatly between the different models. An analysis of the seasonality of MOC in the models and in the observations reveals that MOC anomalies in the models mostly show strong annual cycles at all the latitudes, whereas those derived from Argo and SSH exhibit annual cycles at three latitudes (35°S, 30°S, and to a lesser extent at 25°S) and a semiannual cycle at 20°S.