Pergamon Deep-Sea ResearchI, Vol. 44, No. 5, pp. 793410, 1997 0 1997 Elsevier Science Ltd PII: S0967-0637(96)00117-3 All tights reserved. Printed in Great Britain 09674x37/97 917.00+0.00 Lithogenic fluxes in the Bay of Bengal measured by sediment traps V. RAMASWAMY,* B. VIJAY KUMAR,* G. PARTHIBAN,* V. ITTEKKOTS and R. R. NAIR* (Received I August 1995; in revisedform 12 April 1996; accepted 4 November 1996) Abstract-Lithogenic flux measured continuously for 1 year using time-series sediment traps at two sites in the Bay of Bengal show a strong seasonality with 4349% of the fluxes to the deep traps occurring during the SW monsoon. Lithogenic fluxes increased with depth and the rate of increase was maximum during periods of high freshwater influx. Simultaneous sedimentation of lithogenic and organic matter is seen at both the sites. Clay mineral studies show that illite percentage decrease and smectite percentage increase with depth. Due to the prevailing circulation pattern, illite-rich suspended sediments from the Ganges-Brahmaputra Rivers are transported southwards in the surface low salinity layer while smectite-rich muds from the continental margins are resuspended and transported at depth in perhaps somewhat heavier clock-wise circulation. 0 1997 Elsevier Science Ltd. INTRODUCTION The Bengal Fan, the largest deep sea fan in the world, has been built up mainly by turbidite deposits of the Ganges-Brahmaputra Rivers origin (Kolla and Kidd, 1982; Emmel and Curray, 1984). Sediments from the Ganges-Brahmaputra are transported as far as 8”S, a distance of over 3000 km from the river mouth (Nath et al., 1989). The Ganges- Brahmaputra River systems together with peninsular Indian rivers supply about 1300 km3 of freshwater (Holeman, 1968) and over 1350 million tons of suspended sediments (Milliman and Meade, 1983; Subramanian, 1985; Anon, 1993) to the Bay of Bengal each year (Table 1). This tremendous freshwater influx together with monsoon winds strongly influences the circulation, stratification, productivity and sedimentation patterns in the Bay of Bengal. An earlier study by Ittekkot et al. (1991) documented the effect of freshwater discharge on particle fluxes in the Bay of Bengal. In this paper we describe the fate of terrigenous material discharged into the Bay of Bengal. We have used clay minerals as tracers to distinguish between material derived from the Himalayan rivers (Ganges- Brahmaputra Rivers, having illite content > 70%) and Peninsular Indian rivers (Godavari, Krishna, Mahanadi etc., having high smectite content) (Table 1, Fig. 1). From the clay mineral flux patterns, we have speculated on the processes controlling sedimentation of lithogenic particles in the Bay of Bengal. * Geological Oceanography Division, National Institute of Oceanography, Dona Paula, Goa 403004, India. t Institute of Biogeochemistry and Marine Chemistry, Hamburg University, Bundesstrasse-55, Hamburg, Germany. 793