TROPICS 
(Tropical River-Ocean Processes In Coastal Settings)

GOAL:

To understand mechanisms and establish models of coastal ocean trapping, bypassing, and cycling of solutes and sediments from wet tropical river catchments of high relief (PNG and West Papua) on contrasting coastal shelves. We 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.

STUDY AREAS:

Map of the TROPICS study areas (60 Kb)

Due to high precipitation, great relief, and tectonically active geography, the island of New Guinea (West Papua and Papua New Guinea) contributes more water, solutes, and sediment to the coastal ocean than the Amazon River. The north coast of PNG and West Papua delivers riverine material directly to deep waters of the Bismarck Sea, with little coastal shelf environment. Australian and US marine scientists 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) lead research into the steep shelf of the Mamberamo River region, and the broad shelf and estuary of the Digul River and Arafura Sea.

IndoTROPICS scientific staff in Jakarta 

RESEARCH OBJECTIVES:

1. The biological group 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 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 is used to construct models of the coupling between coastal benthic and pelagic regimes, productivity of mangroves, prawns, finfish, and marine harvestable resources in these contrasting wet tropical sites.
2. The chemical group 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 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 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 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 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 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 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 need to have historical climatic data for each river basin, and some knowledge of changes in land use and population.

At sea we 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, and seafloor currents and sediment resuspension is anticipated. Field operations are planned for 1997-2002.

All investigators agree upon standardized methods for each region, and we 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, MOUs, and in collaboration with Indonesian and PNG governments and scientific institutions.

BENEFITS and PRACTICAL APPLICATIONS:

• Baseline environmental conditions in pristine areas.
• Training, education, and technology transfer in marine environmental science.
• Coastal erosion, turbidity, and sediment transport to regions of coral reefs.
• Information on harbour siltation, seabed stability, and sediment transport along shores.
• Past history and predictions of future climate and sea-level changes.
• Dispersal of nutrients to coastal and oceanic food chains.
• Estimations of biological productivity in estuaries and coastal zone.
• Documentation of importance of mangroves in trapping sediments and nutrients.
• Pathways for contaminant transport in the coastal zone (hydrocarbons, metals).
• Recent history of riverine transport of materials to the coastal zone.
• Estimates of effects of land-use change, development.
• Contributions to global ocean chemical and sedimentary budgets.
• Information on how the coastal zone traps material from the ocean.
• Identification of Indonesian Throughflow and Equatorial Undercurrent tracers.

FACILITIES:

Participating scientists and their institutions have a wide range of laboratory and field equipment for specialized coastal oceanography. These laboratories are listed in the next section. Research vessels from Australia, Indonesia participate. TROPICS scientists have experience in coastal oceanography of the Great Barrier Reef, Gulf of Papua, the Torres Strait, the North-West Shelf of Australia, Sulu and China Sea, the coastal zone of the Amazon River, as well as other non-tropical portions of the world. We welcome suggestions for cooperative research and funding.

For more information about project TROPICS, or a copy of the prospectus, contact
Dr Gregg Brunskill, AIMS
Fax +61 7 4772 5852
e-Mail: g.brunskill@aims.gov.au

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Last updated - December 18, 2008

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