Seasonal and interannual variations of sea surface salinity in the Tropical Pacific ocean

Sea surface bucket measurements, obtained through a ship-of-opportunity program, are used to describe the sea surface salinity (SSS) field for the tropical Pacific during the period 1969-1988. Emphasis is placed upon the mean SSS distribution and the seasonal and internannual SSS variability occuring along four well-sampled shipping tracks. These tracks extend from New Zealand to Japan, from New Zealand to Hawaï, from Tahiti to California, and from Tahiti to Panama. They cross the equator at 155°E, 160°W, 140°W. and 100°W,, respectively. Along each track, the mean SSS distribution is characterized by SSS minima which are 4°-6° further poleward than the axes of maximum precipitation associated with the Intertropical Convergence Zone (ITCZ) and South Pacific Convergence Zone (SPCZ). It is suggested that these SSS minima owe their existence mainly to heavy rainfall and poleman Ekman salt transport associated with the trade winds. The role of zonal salt advection was found negligible for these SSS minima. Except along the eatern track, maximum seasonal variations are located in the ITCZ and SPCZ regions, with minimum SSS in September-October and March-April, respectively. On the basis of precipitation island stations, it is demonstrated that the maximum seasonal SSS variations are closely related to the rainfall regimes of the ITCZ and SPCZ (rainfall maximum 3 months before SSS minimum; rainfall amount sufficient to account for SSS changes). (D'après résumé d'auteur