Sea surface salinity changes along the Fiji-Japan shipping track during the 1996 La Nina and 1997 El Nino period

Sea-surface salinity (SSS) changes during the 1996 La Nina and 1997 El Nino events are analysed along the Fiji-Japan shipping track, based on 20 thermosalinograph sections. In the equatorial band, above-average SSS (35.2 to 35.4 instead of 35) were observed in 1996, consistent with a well-marked south equatorial current, an unusually-strong equatorial upwelling, and below-average precipitation (P). From January to August 1997, the SSS decreased sharply from 35.2 to 33.8 (lowest recorded monthly value over the last 20 years), compatible with a reversal of zonal current, the occurrence of equatorial downwelling, and above-average P. From September to November 1997, the SSS remained almost constant (34.2), consistent with the opposite effects of eastward current, likely bringing low saline water from the Pacific warm pool, and of evaporative cooling, vertical mixing and below-average P which all tend to increase SSS. The potential impacts of the observed SSS changes on sea level are discussed.