Equatorward western boundary transport from the South Pacific: Glider observations, dynamics and consequences

Abstract

Abstract The Solomon Sea carries the equatorward western boundary current of the South Pacific, a principal element of subtropical-equatorial communication. Eighty-seven glider transects across the mouth of the Sea over nine years describe the velocity structure and variability of this system. The time series spans two El Ninos and two La Ninas, which produced large transport anomalies, up to 50% of the mean. While transport increased during El Ninos and decreased during La Ninas, their signatures were inconsistent among the events. Separated glider tracks show the merging of two inflows, one from the tropics east of the Solomon Island chain, the other entering as a western boundary current generated by winds over the full subtropical gyre. A model of linear wind-driven dynamics, including western boundary currents, had skill in describing the variability of the two inflows, identifying the distinct wind forcing driving each. The model suggests that both the mean and low-frequency variability of flow entering the Solomon Sea are driven remotely by wind over the South Pacific, acting through long Rossby waves. The ultimate significance of in situ observations in this small sea will be to describe its role in subtropical-tropical heat exchange that is crucial to ENSO and longer-timescale climate variations along the equator. We take an initial step here, suggesting that temperature advection through the Solomon Sea is a first-order contribution to interannual temperature changes of the equatorial strip as a whole.