Meridional Overturning Transports at 30°S in the Indian and Pacific Oceans in 2002-2003 and 2009

Abstract:

The focus of this work is multi-year differences in meridional transport across 32°S in the combined Indian and Pacific Oceans, using hydrographic sections and velocity observations. Geostrophic velocities and transports are calculated from temperature-salinity profiles collected at stations along the I05 and P06 sections at nominally 32°S in the Indian and Pacific Oceans in 2002-2003 and again in 2009. Velocities observations come from lowered Acoustic Current Profiler (LADCP) and geostrophic reference velocities are obtained from three different inverse models. The most robust difference between 2002 and 2009 in the Indian Ocean, common to all three models and within their uncertainties, is that the SAMW and thermocline transports are shifted to lower densities in 2009. The three models don’t show any difference in the Meridional Overturning Circulation in 2002-2003 and 2009 for the Indian and Pacific Oceans. In contrast, the net southward heat transport across 32°S for the combined Indo-Pacific section is -0.6 to -0.7±0.2 PW in 2002-2003 that is almost doubled for 2009, to -1.3 to -1.5±0.1 PW. The same pattern is observed for the freshwater transports: The net Indo-Pacific freshwater transport convergence is net evaporative for all models and both years, of 0.24 to 0.27 Sv in 2002-2003, which increases to 0.67 to 0.86 Sv in 2009.