Pacific Ocean surface freshwater variability underneath the double ITCZ as seen by satellite sea surface salinity retrievals

摘要

The salinity budget of the upper tropical Pacific Ocean underneath the double Intertropical Convergence Zone (ITCZ) is studied using the Soil Moisture and Ocean Salinity (SMOS) and Aquarius surface salinity observations as well as in situ salinity measurements. In this shallow mixed layer region of the ocean, precipitation effects on the near-surface salinity budget are large, typically leading to a band of fresh sea surface salinity (SSS) between March and June. The role of precipitation during the freshening period is documented here through a direct correlation between the SMOS SSS fields and the monthly accumulated precipitation. During the same period, the mixed layer salinity budget is impacted by advection, which, based on in situ observations, is found to be another important mechanism for the evolution of the near-surface salinity as documented through a connection between the north equatorial eastern Pacific Fresh water pool and this south equatorial freshwater pattern in boreal spring. However, given the information at hand, the near-surface salinity budget cannot be closed, suggesting that other processes are important too, such as nonlinear effects, mixing, and entrainment.