Monsoon control on trace metal fluxes in the deep Arabian Sea

摘要

Particulate ???uxes of aluminium,iron,magnesium and titanium were measured using six time-series sediment traps deployed in the eastern, central and western Arabian Sea. Annual Al ???uxes at shallow and deep trap depths were 0.47 and 0.46 gma?’2 in the western Arabian Sea,and 0.33 and 0.47 g ma?’2 in the eastern Arabian Sea. There is a difference of about 0.9-1.8gma?’2 ya?’1 in the lithogenic ???uxes determined analytically (residue remaining after leaching out all biogenic particles) and estimated from the Al ???uxes in the western Arabian Sea. This arises due to higher ???uxes of Mg (as dolomite) in the western Arabian Sea (6-11 times higher than the eastern Arabian Sea). The estimated dolomite ???uxes at the western Arabian Sea site range from 0.9 to 1.35gma?’2 ya?’1. Fe ???uxes in the Arabian Sea were less than that of the reported atmospheric ???uxes without any evidence for the presence of labile fraction/excess of Fe in the settling particles. More than 75% of Al, Fe, Ti and Mg ???uxes occurred during the southwest (SW) monsoon in the western Arabian Sea. In the eastern Arabian Sea, peak Al, Fe, Mg and Ti ???uxes were recorded during both the northeast (NE) and SW monsoons. During the SW monsoon, there exists a time lag of around one month between the increases in lithogenic and dolomite ???uxes. Total lithogenic ???uxes increase when the southern branch of dust bearing northwesterlies is dragged by the SW monsoon winds to the trap locations. However, the dolomite ???uxes increase only when the northern branch of the northwesterlies (which carries a huge amount of dolomite accounting 60% of the total dust load) is dragged, from further north, by SW monsoon winds. The potential for the use of Mg/Fe ratio as a paleo-monsoonal proxy is examined.