a) Expanded high resolution bathymetry of the central part of the Southern Trough with location of fluid-emission acoustic images described in the text (black circles and squares) and their maximum altitude above the seafloor. The main vent sites are named. Red triangles indicate the point where oil discharges have been seen (see Fig. 6). b) Annotated structural interpretation of the same area shown in a) superimposed on an acoustic backscatter image. The black lines labeled P4 and P5 are the AUV sub-bottom profiles.