Carbon-isotope composition of sediments from the Gulf of Papua

Abstract

Rivers draining into the Gulf of Papua (GOP) from the Papua New Guinea mainland deliver approximately 340 × 106 t yr−1 of sediment to the marine environment. The terrestrially derived sediment contains 1.1 ± 0.2% particulate organic carbon with a carbon-isotope composition of −26.5 ± 0.2‰, and amounts to 3.7 ± 0.7 × 106 t yr−1. The carbon-isotope composition of sediments in the Gulf of Papua indicates that 40% of the sediment cover contains 75% or more terrestrially derived carbon. Suspended sediments that are transported beyond the delta complex of the Fly River are transported north and northwest, augmented by sediments from other rivers along the coast of the GOP. The carbon-isotope results suggest that a significant quantity of terrestrially derived sediment escapes from the GOP, either along the coastlines to east and west or into the deep ocean via the Moresby and Pandora troughs. Little sediment travels south onto the Great Barrier Reef shelf. Extrapolating the results from this study to the region of Oceania suggests a total flux of particulate organic carbon to the world's oceans from the islands of Oceania of ~ 90 × 106 t yr−1 or twice the flux of riverine POC from the major rivers of North America, South America, and Africa combined. While such a calculation must be considered illustrative only, the similar tectonic, geomorphologic, and climatic features of the islands of Oceania suggest that the calculation is unlikely to be grossly in error and that the rivers of Oceania therefore represent a major but poorly documented source of sediment and organic carbon to the global ocean.