New multi-channel seismic reflection data acquired in the southwest Indian Ocean is used to evaluate the basement structure and the origin of the southern Mozambique Ridge (MozR). Another objective of the interpretation of the data is to investigate the possible impact of the structure on palaeocean circulation in the evolving Southern Ocean. Investigation of the new geophysical data shows the occurrence of extensive lava flow sequences and a great number of extrusion centres. The observations suggest a Large Igneous Province origin of the southern MozR and its emplacement between 131 and 125 Ma. The sedimentary record in the area of the southern MozR acts as an archive for the water mass exchange between the Indian and South Atlantic Oceans through the African-Southern Ocean gateway. Characteristic sedimentary structures are deposited by current-controlled sedimentation and allow for an interpretation of the intensity, pathway and direction of the palaeocean circulation. The observations document the evolution from a restricted circulation during the Cretaceous towards an open marine circulation during Neogene and Quaternary times within the gateway.