Current structure of the south Indian Ocean

Using recently published atlas data [Olbers et al., 1992] and the Fine Resolution Antarctic Model (FRAM) [Webb er al., 1991], an investigation has been conducted into the structure of the frontal jets centered around the region of the islands of Crozet (46 degrees 27'S, 52 degrees 0'E) and Kerguelen (48 degrees 15'S, 69 degrees 10'E) in the south Indian Ocean. Geostrophic current velocities and transports were calculated from the temperature and salinity fields available from the atlas and compared with results from FRAM and previous studies. We have identified the Agulhas Return Front (ARF) and the Subtropical Front (STF), as well as the following fronts of the Antarctic Circumpolar Current (ACC): the Subantarctic Front (SAF), the Polar Front (PF), and the Southern ACC Front (SACCF), from temperature and salinity characteristics and from geostrophic currents. This analysis of model and atlas data indicates that the jets associated with the ARF, STF, and SAF are topographically steered into a unique frontal system north of the islands, having some of the largest temperature and salinity gradients anywhere in the world ocean. The frontal jet associated with the ARF is detectable up to 75 degrees E and has associated with it several northward branching jets. The PF bifurcates in the region of the Ob'Lena (Conrad) seamount; subsurface and surface expressions are identified, separated by as much as 8 degrees of latitude immediately west of the Kerguelen Plateau. The surface expression, carrying the bulk of the transport (similar to 65 Sv), is steered through the col in the Kerguelen Plateau at 56 degrees S, 6 degrees south of the latitude normally associated with the PF at this meridian. On crossing the plateau it rejoins the subsurface expression. In the south, passing eastward along the margin of the Antarctic continent and through the Princess Elizabeth Trough, a frontal jet is identified transporting up to 35 Sv, believed to be the SACCF [Orsi et al., 1995], placing the southern extent of the ACC in the region at 67 degrees S.