Terrigenous plant wax inputs to the Arabian Sea: Implications for the reconstruction of winds associated with the Indian Monsoon

We have determined the accumulation rates and carbon isotopic compositions (δ13C) of long-chain (C24–C32) terrigenous plant wax fatty acids in 19 surface sediment samples geographically distributed throughout the Arabian Sea in order to assess the relationship between plant wax inputs and the surrounding monsoon wind systems. Both the accumulation rate data and the δ13C data show that there are three primary eolian sources of plant waxes to the Arabian Sea: Africa, Asia, and the Arabian Peninsula. These sources correspond to the three major wind systems in this region: the summer (Southwest) monsoon, the winter (Northeast) monsoon, and the summer northwesterlies that blow over the Arabian Peninsula. In addition, plant waxes are fluvially supplied to the Gulf of Oman and the Eastern African margin by nearby rivers. Plant wax δ13C values reflect the vegetation types of the continental source regions. Greater than 75% of the waxes from Africa and Asia are derived from C4 plants. Waxes delivered by northwesterly winds reflect a greater influence (25–40%) of C3 vegetation, likely derived from the Mesopotamian region. These data agree well with previously published studies of eolian dust deposition, particularly of dolomite derived from the Arabian Peninsula and the Mesopotamian region, in surface sediments of the Arabian Sea. The west-to-east gradient of plant wax δ13C and dolomite accumulation rates are separately useful indicators of the relationship between the northwesterly winds and the winds of the Southwest monsoon. Combined, however, these two proxies could provide a powerful tool for the reconstruction of both southwest monsoon strength as well as Mesopotamian aridity.