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Kido, S., and Tozuka, T. (16-Dec-16)

Sea surface salinity (SSS) in the tropical Indian Ocean undergoes large interannual variations associated with the Indian Ocean Dipole (IOD), but their impacts on the upper-ocean stratification and sea surface temperature (SST) are not fully understood. Here, using a 1-D turbulence closure model, a series of sensitivity experiments with and without salinity anomalies is carried out to quantify their impacts during positive IOD events. In the central-eastern tropical Indian Ocean, a combination of negative SSS anomalies and positive subsurface salinity anomalies strengthens the upper ocean stratification during positive IOD events. As a result, vertical mixing is suppressed and significant warming of ~0.5℃ occurs. On the other hand, weakening of salinity stratification caused by near surface positive salinity anomalies in the southwestern tropical Indian Ocean enhances vertical mixing and results in cooling (~-0.2℃). Our results suggest that variations in salinity stratification may potentially play a crucial role in the evolution of positive IOD events.