Wind-Driven Changes of Current, Temperature, and Chlorophyll Observed by Satellites North of New Guinea

We investigate the physical and biological variability of the ocean in the Bismarck Sea, north of New Guinea, taking advantage of the high spatio-temporal resolution of satellite data to expand on past studies. Based on scarce cruise and mooring data, a trade wind situation (austral winter) and a northwest monsoon situation (austral summer) were differentiated; the New Guinea Coastal Current (NGCC) flows northwestward in winter and a coastal upwelling develops and the NGCC reverses in summer. Here, satellite observations confirm that the NGCC intensifies during the trade wind season and reverses in summer, except in Vitiaz Strait where the surface northwestward flow persists. Wavelet analyses of satellite-derived wind and currents, sea surface temperature (SST), and chlorophyll show that intraseasonal and seasonal time scale variations explain most of the variance north of New Guinea. The combination of satellite observations further shows that SST and chlorophyll variability is mainly driven by two processes: coastal upwelling and penetration of Solomon Sea water. Coastal upwelling is generated when winds are westerly (westerly wind event, northwest monsoon). Intraseasonal westerly wind events are most active seasonally between September and January and interannually during El Niño events. Upwelled coastal waters spread towards the equator and, during some westerly wind events, these phytoplankton-rich waters can be advected toward the eastern part of the warm pool by the surface current. Penetration of Solomon Sea water occurs during the trade wind situation when enhanced NGCC transports cold water through Vitiaz Strait in a narrow vein hugging the coast. At the interannual time scale, the upwelling influence in the Bismarck Sea combines with the coastal cold tongue influence on lowering SST and counteracts the penetration of low chlorophyll water from the Solomon Sea during El Niño. Below are maps showing the SST, wind stress, chlorophyll, and altimetric current anomaly patterns when upwelling (August) and penetration of Solomon Sea water (February) are active.