Estimating a time series of meridional heat transport of the Indian Ocean at 34°S

The meridional heat transport of the South Indian Ocean is climatically important. Heat transported southward out of the Indian Ocean basin may travel into the Atlantic through Agulhas Leakage, or may impact the Southern Ocean. Historically, heat transport has been calculated using cross basin hydrographic sections in conjunction with inverse models. However, sufficient data to calculate the heat transport of the South Indian Ocean using this method has only been collected three times (1987, 2002, 2009). Here, we present a 25 month time series of the heat transport of the South Indian Ocean at 34°S. This estimate is produced by combining mooring data of the Agulhas Current with Argo and satellite data of the interior South Indian Ocean. Wind reanalysis data are used to calculate the Ekman flow, and historical hydrographic data are used to estimate flow below 2000 dbar. As a warm, fast western boundary current, the Agulhas Current dominates the heat budget of the basin. The temperature, salinity, and velocity of the Agulhas Current were observed using 7 tall moorings and 5 CPIES as part of the Agulhas System Climate Array (ASCA). These measurements show that the Agulhas Current carries a temperature transport of 3.7 PW southwards - more than 3 times the temperature transport of the Indonesian Throughflow. The temperature transport of the Agulhas Current primarily varies advectively, with a stronger current carrying more heat. 25% of the variability in the temperature field is described by this advective effect. Combining the western boundary data with data across the South Indian Ocean, we estimate a time series of the basin wide heat transport and compare it to previous estimates of heat transport at discrete points in time.