Key Points  A century-long reconstructed South Atlantic Meridional Overturning Circulation index from sea surface temperature is presented.  The Interdecadal Pacific Oscillation and Atlantic Niño are the main contributors of interannual/decadal covariability of SST and SAMOC.  SAMOC is currently in an anomalous positive phase. Abstract This study reconstructs a century-long South Atlantic Meridional Overturning Circulation (SAMOC) index. The reconstruction is possible due to its

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... with sea surface temperature (SST). A singular value decomposition (SVD) method is applied to the correlation matrix of SST and SAMOC. The SVD is performed on the trained period (1993present) for which Expendable Bathythermographs (XBT) and satellite altimetry observations are available. The joint modes obtained are used in the reconstruction of a monthly SAMOC timeseries from 1870 to present. The reconstructed index is highly correlated to the observational-based SAMOC timeseries during the trained period and provides a long historical estimate. It is shown that the Interdecadal Pacific Oscillation (IPO) is the leading mode of SAMOC-SST covariability, explaining ~85% with the Atlantic Niño accounting for less than 10%. The reconstruction shows that SAMOC has recently shifted to an anomalous positive period, consistent with a recent positive shift of the IPO.