The heat transport of the Indonesian Throughflow and implications for the Indian Ocean heat budget

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Abstract The Indonesian Throughflow (ITF) is considered central to the heat budgets of the Pacific and Indian Oceans. Temperature and ocean current time series obtained within the Makassar Strait from December 1996 to early July 1998 are used to calculate heat transport of the ITF and assess its influence on Indian Ocean heat divergence. Velocity and temperature values for the surface layer that were not directly measured are extrapolated from the shallowest measurement to the sea surface using a variety of model profiles. While a single temperature profile is used based on a linear interpolation from NCEP OI sea-surface temperatures to the top-most mooring temperature recorder, four different velocity profiles are employed. Heat transport is calculated as volume transport multiplied by temperature, density and specific heat, using reference temperatures between 0°C and 4°C. The mean heat transport averages 0.55 PW relative to 0°C, and 0.41 PW relative to 4°C for the two most reasonable velocity profiles. In comparison, model heat transport values are larger, between 0.6 and 1.15 PW. Heat transport varies with ENSO phase, lower during El Nino, higher during La Nina. As 1997 was a strong El Nino year, our heat transport estimate may be less than the climatic mean. The ITF water is advected towards Africa within the Indian Ocean South Equatorial Current, to eventually exit the Indian Ocean across 30°S, most likely within the Agulhas Current. For realistic consideration of the ITF component within the Agulhas Current, the heat flux divergence of ITF waters within the Indian Ocean north of 30°S is found to be insignificant. Our results provide support for model studies and hydrographic geostrophic inverse calculations that indicate the ITF heat, derived from the Pacific Ocean, is ultimately lost to the atmosphere in the southwest Indian Ocean.