Spreading of red sea overflow waters in the Indian ocean

As a result of its remarkably high salinity and despite its small volume in put, remnants of Red Sea Water (RSW) have been identified in the Agulhas Cu rrent, over 6000 km distant of their source. This provided the motivation t o investigate the long-term mean spreading of RSW throughout the Indian Oce an, using a comprehensive set of observations, taken from the National Ocea nographic Data Center archives and from the World Ocean Circulation Experim ent Hydrographic Program for the Indian Ocean. After emerging from the Gulf of Aden into the Arabian Sea, RSW spreads predominantly southwestward alon g the African continental slope, as indicated by strongly inclined isohalin es across the Arabian Sea. There is some monsoon variability, so that durin g the winter monsoon there is more RSW present in the Gulf of Aden and an i ntensification of southward spreading along the western boundary, between 1 2 degrees and 5 degrees N. Elsewhere the intermediate depth salinity field of the Indian Ocean appears relatively stationary Between 5 degrees and 10 degrees S, in the region of the South Equatorial Current, isohalines of the RSW layer become quasi-zonal across the width of the Indian Ocean, only di pping southward toward the western boundary west of 50 degrees E. South of here, there is a strong tongue of RSW spreading southward through the Mozam bique Channel and into the Agulhas Current. These conclusions concur with p revious localized investigations of intermediate water properties. Using a simple mixing model, the percentage of RSW throughout the Indian Ocean was quantified. It was found that the flux of salt into the Gulf of Aden from t he Red Sea is similar to that estimated to cross 32 degrees S in the Agulha s Current. This result implies that all the RSW which is mixed into the int erior of the Indian Ocean may eventually be exported at the western boundar y. Furthermore, it implies that RSW is the dominant component of the salt b udget for the intermediate layer and that input from the Indonesian Seas an d via diapycnic processes are small.