GOAL:

To understand mechanisms and establish models of coastal ocean trapping, bypassing, and cycling of solutes and sediments from a wet tropical area of high relief (PNG and Irian Jaya) on contrasting coastal shelves. We will determine the processes that control the dispersal of wet tropical riverine dissolved and particulate material into the coastal ocean, and how these processes affect estuarine, deltaic, coastal, shelf and slope productivity, marine resources, and sustainable development options.

PROPOSED STUDY AREAS:

Due to high precipitation, great relief, and tectonically active geography, the island of New Guinea (Irian Jaya and Papua New Guinea) contributes more water, solutes, and sediment to the coastal ocean than the Amazon River. The north coast of PNG and Irian Jaya delivers riverine material directly to deep waters of the Bismarck Sea, with little coastal shelf environment. Australian and US marine scientists will lead studies of the Sepik River estuary and coastal ocean plume in this region. In contrast, the Fly and Purari Rivers of the south coast of Papua New Guinea drain the same mountain ranges, but discharge into broad swampy alluvial plains, long estuaries, and a broad, shallow continental shelf.

Indonesian marine scientists (IndoTROPICS) will lead research into the steep shelf of the Mamberamo River region, the mangrove-lined Bay of Bintuni, and the broad shelf and estuary of the Digul River and Arafura Sea.

RESEARCH OBJECTIVES:

1. The biological group will quantify and model the differences in the production and decomposition of organic matter in the water column and seabed at these very different coastal sites. They will quantify how biological processes and communities are affected by sediment-water exchanges, and how terrestrial and marine organic matter is decomposed or preserved in the sediments. This work will be used to construct models of how the coupling between coastal benthic and pelagic regimes influences productivity of mangroves, prawns, finfish, and marine mammal harvestible resources in these contrasting wet tropical sites.

2. The chemical group will quantify and model the reactions of rapidly transported weathering products from these similar river basins to very different estuary and shelf environments, including the release and uptake of nutrients, trace elements, and organic biomarkers. There is extremely high annual loading of suspended sediments in these estuaries and coastal zones, and we will determine the estuarine and shelf trapping efficiency for riverine dissolved and particulate elements. For the same reasons, we expect to see spectacular scavenging of oceanic elements in some of these particle-rich coastal zones. We will determine the recent (Holocene) history of coastal geochemical processes from sediment and coral cores. Chemical tracers for the Indonesian Throughflow and Equatorial Undercurrent will be sought.

3. The physical oceanographic group will quantify and model the variations in physical structure and processes that control the trapping and cycling of riverine and oceanic elements in contrasting narrow and wide continental shelves. We will describe and model the roles of flocculation, tidal pumping, waves, 3-dimensional estuarine structure and circulation, multiple riverine sources, and fronts in particle trapping. We plan to determine how bottom stress from currents and waves influences grain-size distribution in surficial sediment and suspended sediment, and what processes lead to patchiness of river plumes and bottom sediments. We want to study the roles of surface and internal waves as a forcing function in water mass mixing and river plume dynamics, and how this regional mixing and circulation affects near- and far-field flow. These forces control the coastal dispersal of dissolved and particulate riverine material.

4. The geological group will study Holocene contrasts between foreland and leading-edge margin sedimentation, with emphasis on sediment partitioning between the estuaries, shelves, slopes, and the deep sea. Of particular interest will be the special aspects of continental-margin sediment dispersal from distributed sources (multiple large riverine inputs) to very different continental-margin bathymetries. Present gradients from riverine clastic sediments to marine carbonate sediment zones will be used to interpret the history of variations of these sediment types in cores, which represent changes in runoff, sediment stability, and dispersal paths. The north coast of New Guinea is an analog for all rivers in understanding sediment dispersal during low sea-level stands previous to 6000 years ago.

METHODS and APPROACHES:

We will need land-based teams of investigators, for estimations of riverine discharge of water, dissolved materials, and sediments, and coring operations to discover the recent history of sedimentation in alluvial valleys, deltas, and mangrove swamps. We will need to have historical climatic data for each river basin, and some knowledge of changes in land use and population.

At sea we will use standard oceanographic equipment on large and small vessels suitable for the coastal region. Short-(weeks) and long-term (months) deployments will be made for tide, current, wave, sediment, and chemical measurements. The use of specialized equipment for large volume water sampling, seafloor biological and geochemical measurements (lander), and seafloor currents and sediment resuspension is anticipated. Field operations are planned for 1997-2000.

All investigators will agree upon standardized methods for each region, and we will utilize a standard sampling grid for each region, to enable direct comparisons of results. The resulting database will be available to all collaborators. Type specimens and reference collections will be made available to Indonesian and Papua New Guinean authorities. All research will be done with in accordance with Research Agreements and in collaboration with Indonesian and PNG governments and scientific institutions.

BENEFITS and PRACTICAL APPLICATIONS: