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

Abstract

This paper reviews work on the currents of northern Papua New Guinea and then 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 reaches 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 Britain 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 PNG 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 ~10 km at 1 m s–1 before being turned to the NW by the underlying currents. 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. During 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 comprised of stacks of many mixed layers, with enhanced loads of suspended sediment at the bases of most of them. These subsurface sediment plumes became depleted with increasing distance offshore. Although the tides in the region are small, moored instruments showed semi-diurnal internal tidal currents 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 subsurface flows at the sills.