Scripps Institution of Oceanography

Commencing in 1987, an international panel of sea-going scientists has collaborated in compiling and interpreting all available sea floor topographic, magnetic and satellite-derived gravity data in the Indian Ocean overall, from sow to 1660E and from Africa-Asia-Australia south to Antarctica. The purpose of the project is to evaluate uniformly comparable data from academic and agency sources, to provide large scale working charts of these compilations and to produce a detailed digital state-of-the art tectonic chart for the entire Indian and contiguous Southern Oceans.

The compilations and the tectonic chart will be used to reconstruct the history of the seafloor and the continents surrounding these oceans. This technical report, Part 1 of the project, provides the data compilation plots and the tectonic chart for the southwestern Indian Ocean which lies between southern Africa and Antarctica. Lying between 31 o S and 71 o S, and sow and 71 OE, it represents almost one third of the entire area of the Indian Ocean and the contiguous Southern Oceans.

The topographic contours portray the shape and relief of the sea floor itself. They also display well the long-wavelength depth anomalies such as oceanic plateaus and swells. The satellite-derived gravity field does not resolve local fine detail but reflects the longer wavelength (> 20 km) density contrasts beneath the oceans. Like the bathymetry, it is dominated in the Southwest Indian Ocean by the spreading ridge axis, the active transform faults and the major fracture zones. It also reveals the sediment-covered extension of these fracture zones and the basement relief of the oceanic plateaus. Identification of magnetic anomaly data permits the determination of the age of the oceanic crust. The three data bases, combined and abstracted into a tectonic chart, together present a very clear summary of the present overall morphology of the ocean floor and also reveal the masking effects of sedimentation. They present a unique data base from which to reconstruct the history of the seafloor in the southwestern Indian Ocean.