Flux and fate of fluvial sediments leaving large islands in the East Indies

Because of their generally small drainage basin areas, high topographic rel ief, relatively young and erodible rocks, and heavy rainfall, rivers draini ng the high-standing islands of the East Indies transport a disproportionat ely large amount of sediment to the ocean. Rivers on the islands of Sumater a (Sumatra), Jawa (Java), Borneo, Sulawesi (Celebes), Timor and New Guinea are calculated to discharge about 4.2 x 10(9) t of sediment annually. Altho ugh these six islands only account for about 2% of the land area draining i nto the global ocean, they may be responsible for as much as 20 to 25% of t he sediment export. Fluvial sediment leaving these islands is discharged in to several distinctly different provinces: shallow epicontinental seas such as the Sunda Shelf, Gulf of Papua and Sea of Arafura; and narrow-shelf, ac tive margins along the western and southern sides of Sumatra and Java, and the north coast of New Guinea. High-resolution seismic profiles in the Gulf of Papua (New Guinea) show a clinoform sequence of Holocene sediments pinc hing out on the mid- to outer shelf, with sediment thickness locally greate r than 40 m near the coast; some - but perhaps not much - sediment escapes to the outer shelf and the deeper Papua Trough beyond. In contrast, seismic profiles off northern New Guinea show river-derived sediment prograding ov er and by-passing a narrow shelf that locally has buried a relict barrier r eef. A small fraction of the sediment escaping the northern shelf may be tr ansported to the eastern equatorial Pacific by way of the Equatorial Counte r Current, where it may help fertilize equatorial upwelling. (C) 1999 Elsev ier Science B.V. All rights reserved.