Coastal currents of northern Papua New Guinea, and the Sepik River outflow

This paper reviews work on the currents of northern Papua New Guinea and th en examines recent observations with a research vessel, moored instruments, simple drifters, and NOAA satellite AVHRR and RADARSAT synthetic aperture radar (SAR) imagery. The dominant large scale features are: the strong New Guinea Coastal Undercurrent that flows through Vitiaz Strait and then reach es along the coast towards Irian Jaya; the New Guinea Coastal Current that reverses with the monsoons; and a wind-driven upwelling plume from SW New B ritain during the SE monsoon that joins Solomon Sea waters to flow through Vitiaz Str to bathe the offshore islands, as well as spreading along the PN G coast. During the ship survey in the SE monsoon season the surface plume from the Sepik River was only about 2 m thick and it moved offshore similar to 10 km at 1 m s(-1) before being turned to the NW by the underlying curr ents. A coincident SAR scene provided a large-scale snapshot of the plume. The plume switched to flow SE at the end of the several-day ship survey. Du ring the NW monsoon another SAR scene showed the plume streaming to the SE. The waters down to several hundred metres in the Sepik study area were com prised of stacks of many mixed layers, with enhanced loads of suspended sed iment at the bases of most of them. These subsurface sediment plumes became depleted with increasing distance offshore. Although the tides in the regi on are small, moored instruments showed semi-diurnal internal tidal current s to have amplitudes up to 0.15 m s(-1) and to be associated with vertical oscillations of perhaps 40-50 m. The waters of Goodenough Basin in eastern PNG were mixed from 500 m to the bottom at 1300 m, with energetic subsurfac e flows at the sills.