Monsoon control on trace metal fluxes in the deep Arabian Sea |
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Authors: | T M Balakrishnan Nair |
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Institution: | (1) Indian National Centre for Ocean Information Services (INCOIS), Ministry of Ocean Development, ‘Ocean Valley’, IDA-Jeedimetla (P.O.), 500 055 Hyderabad, India |
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Abstract: | Particulate fluxes 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 fluxes at shallow and deep trap depths were 0.47 and 0.46 g m-2 in the western Arabian Sea, and 0.33 and 0.47 g m-2 in the eastern Arabian Sea. There is a difference of about 0.9–1.8 g m-2y-1 in the lithogenic fluxes determined analytically (residue remaining after leaching out all biogenic particles) and estimated
from the Al fluxes in the western Arabian Sea. This arises due to higher fluxes of Mg (as dolomite) in the western Arabian
Sea (6–11 times higher than the eastern Arabian Sea). The estimated dolomite fluxes at the western Arabian Sea site range
from 0.9 to 1.35gm-2y-1. Fe fluxes in the Arabian Sea were less than that of the reported atmospheric fluxes 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 fluxes occurred during the southwest
(SW) monsoon in the western Arabian Sea. In the eastern Arabian Sea, peak Al, Fe, Mg and Ti fluxes 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 fluxes. Total lithogenic fluxes increase when the southern branch of dust bearing northwesterlies
is dragged by the SW monsoon winds to the trap locations. However, the dolomite fluxes 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. |
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Keywords: | Monsoon fluxes trace metal Arabian Sea aerosol proxies |
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