Observational evidence for a Southern Hemisphere oceanic supergyre

A high-resolution hydrographic atlas resolves the narrow boundary flow of the western Pacific gyre and its pathway around Tasmania, southern Australia and into the Indian Ocean basin. This confirms recent model descriptions of a Southern Hemisphere 'supergyre', a nested system of subtropical gyres. The observations show that the gyre flow is squeezed into a narrow band between Tasmania and the Antarctic Circumpolar Current. The residue of East Australian Current transport turns westward around Tasmania and 'leaks' into the Indian Ocean. While there is also a limited form of gyre connection between the Indian and Atlantic systems south of Africa, with a mean outflow of Agulhas Current water into the Atlantic basin, these gyre circulations remain far more discrete. The gyre coupling and the East Australian Current in particular, provide the mechanism by which Sub Antarctic Mode Water and Antarctic Intermediate Water are distributed between the ocean basins.