INTRODUCTION Continental margin deposits represent important archives of Earth his- tory, recording changes in climate, tectonics, and eustasy. However, inter- pretations of this sedimentary record are only accurate to the degree that local and global signals can be separated. One of the persistent limitations in this deconvolution process is our vague constraint on the variability of river- ine sediment discharge. In high latitudes, dramatic glacial to interglacial dif- ferences in river discharge and sediment load are well recognized, particu- larly as related to catastrophic flood pulses during deglaciation (Emiliani et al., 1978). However, in terms of global sediment budgets, low-latitude rivers are more significant because of higher runoff and sediment yields (Milliman and Syvitski, 1992). These low-latitude systems also show strong climate-driven shifts during the late Quaternary, with major changes in paleohydrology and sediment transport patterns noted during the height of the glacial-interglacial transition 18000–7000 yr B.P. (Gingele, 1996; Turcq et al., 1997). These and other studies have further stressed the apparent con- nection between tropical and subtropical river behavior and strengthened summer monsoon circulation in the early Holocene (Schneider et al., 1997; Thomas and Thorp, 1995). However, none of these investigations have had the opportunity to quantify changes in sediment discharge, particularly as a flux to the margin. In this study we take advantage of opportunities pre- sented by the Ganges-Brahmaputra system to quantify late Quaternary changes in sediment discharge and to address their patterns and likely cause. GANGES-BRAHMAPUTRA SEDIMENT DISPERSAL The Ganges-Brahmaputra River currently transports ~1 × 10 9 t/yr of sediment to the margin, ranking it first along with the Amazon among the world's rivers (Milliman and Syvitski, 1992). About 80% of this load is de- livered during the southwest monsoon from June to September (Coleman, 1969), making the system particularly sensitive to regional-scale climatic forcing. At the continental margin, the river’s sediment load is received in the Bengal basin, which comprises ~1 × 10 5 km 2 of flood-plain and delta-plain environments. During the last glacial maximum, this region consisted of ex- posed uplands and incised valleys that connected with the Bengal fan via the Swatch of No Ground canyon (Fig. 1). River discharge appears to have been greatly reduced at this time as a result of a weak southwest monsoon and arid conditions in Tibet and the Himalayas (Duplessy, 1982; Van Campo, 1986). Evidence for a weak monsoon includes high surface-water salinities in the northern Bay of Bengal (Cullen, 1981), the formation of ooid shoals on the outer Bengal shelf (Wiedicke et al., 1999), and an apparent absence of sedi- mentation on the Bengal fan. By ca. 15000 yr B.P. active sedimentation be- gan on the fan, and rates continued to increase over the next several thousand years (Weber et al., 1997). This growing flux of sediment to the deep sea cor- responds with the start of increased precipitation in Tibet (Gasse et al., 1991), suggesting that river sediment discharge had increased but bypassed the shelf to the upper fan. After ca. 11000 yr B.P. there was a precipitous drop in fan sedimentation (Weber et al., 1997) as a result of rising sea level and the trap- ping of Ganges-Brahmaputra sediment on the flooded Bengal margin. During early delta formation from ca. 11000 to 7000 yr B.P., river- sediment flux was sufficient to infill accommodation generated by rapid sea-level rise, leading to ~50 m of vertical aggradation (Goodbred and Kuehl, 2000). By the middle Holocene, decelerating sea-level rise favored subaerial delta progradation and development of a subaqueous delta on the shelf (Kuehl et al., 1997). During the past 7000 yr of relative highstand, Ganges-Brahmaputra sediments have been almost equally partitioned across the margin, with roughly thirds of the total load each being deposited Geology; December 2000; v. 28; no. 12; p. 1083–1086; 4 figures; 1 table. 1083 Enormous Ganges-Brahmaputra sediment discharge during strengthened early Holocene monsoon Steven L. Goodbred Jr.* Marine Sciences Research Center, State University of New York, Stony Brook, New York 11794-5000, USA Steven A. Kuehl Virginia Institute of Marine Science, College of William and Mary, Gloucester Point, Virginia 23062, USA ABSTRACT Rivers are the main source of terrigenous sediment delivered to continental margins and thus exert a major control on coastal evolution and sequence development. However, little is known about past changes in fluvial sediment loads despite the recognition of significant varia- tion under changing climatic regimes. In this study we present the first quantified estimate of sediment discharge for a major river system under conditions of an intensified early Holocene monsoon. Development of the Ganges-Brahmaputra River delta began ca. 11000 yr B.P., when rising sea level flooded the Bengal basin, thereby trapping most of the river’s discharge on the inner margin. Chronostratigraphic data from these deltaic deposits are used to calculate the rates of sediment storage on the margin, which provide a minimum estimate of the river’s past sediment load. Results reveal that ~5 × 10 12 m 3 of sediment was stored in the Bengal basin from ca. 11000 to 7000 yr B.P., which corresponds to a mean load of 2.3 × 10 9 t/yr. In comparison, modern sediment load of the Ganges-Brahmaputra is ~1 × 10 9 t/yr, ranking it first among the world’s rivers and underscoring the significance of a two-fold increase sustained over 4 k.y. Furthermore, the timing of immense discharge in the early Holocene strongly suggests its relation to a stronger than present southwest monsoon in South Asia. Similar patterns of high monsoon-related sediment discharge have been noted throughout the tropics and subtropics, suggesting a widespread fluviosedimentary response, the potential magnitude of which is show- cased by the Ganges-Brahmaputra system. Keywords: climate effects, deltaic sedimentation, river discharge, sediment budget, Ganges- Brahmaputra River. *E-mail: sgoodbred@notes.cc.sunysb.edu.