The JADE and WOCE I10/IR6 Throughflow sections in the southeast Indian Ocean. Part 2: velocity and transports

Abstract

Abstract Velocity and transports are estimated for five recent hydrographic sections and one full-depth velocity section that cross the Indonesian Throughflow in the southeast Indian Ocean between Australia and Indonesia. The sections are: JADE August 1989 and JADE February 1992, both between northwestern Australia and Bali; WOCE repeat sections IR6 April 1995, IR6 September 1995 and I10 November 1995, all between Western Australia to near Sunda Strait, Java. The three WOCE surveys include direct velocity measurements from shipboard and lowered (I10 only) acoustic Doppler current profilers. None of the WOCE hydrographic surveys measured the Indonesian Exclusive Economic Zone between ∼9°S and the Java coast. Concurrent XBT and XCTD observations taken as part of the regular co-located IX1-XBT transect were used to complete the sections. Both the velocity fields and the transport estimates vary widely in magnitude and direction, and reflect the seasonal and the shorter-term variability from the eddy field at the time of each survey. The eddies are found during each of the WOCE surveys in the South Equatorial Current between 14°S–12°S, and have a significant impact on the velocity structure: the mass transport tends to recirculate within the features. The direct current estimates support the finding that the strongest flow across all sections is found within the eddy structures, as well as in the South Java Current that flows along the Java coastline. The semi-annually reversing South Java Current plays an important role in distributing freshwater into and out of the southeast Indian Ocean. The errors and uncertainties of the transport calculations are assessed in terms of salinity variability in the region using different available salinity fields. For the shallow-layer transport, a new mean historical salinity estimate does a good job of reproducing the transports determined from synoptically available fields. However, for deeper reference layers, the presence of the eddies significantly affects the salinity and therefore the transport estimates in the region.