We have compared the travel times of direct (P, S) and core-reflected (PcP, ScS) phases recorded in southern Africa from earthquakes occurring in the Scotia Arc region. The low-velocity region beneath the south Atlantic is explored by calculating ScS-S and PcP-P travel-time residuals to determine the correlation and magnitude of Vs and Vp reductions in the deepest mantle. Residual calculations yield extraordinary results as PcP-P is about 1 second larger than expected while ScS-S is >7 seconds larger for a great circle arc distance of 54¿. We investigate models of P and S velocity reductions in the deepest mantle that may explain these residuals to provide constraints on the velocity structure of the D region in this extremely slow zone. The reductions in P and S velocity needed to match the data are consistent with partial melting in the deepest mantle for a wide range of 1D models.