Analysis of sup(210)Pb in sediment trap samples and sediments from the northern Arabian Sea: Evidence for boundary scavenging
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The concentrations of sup(210)Pb were measured in particles intercepted by sediment traps deployed at 1024 m and 3024 m in the northern Arabian Sea for a period of 1 year from November 1986 to October 1987. The sup(210)Pb activity in the biweekly samples varied from 11 to 108 dpm g sup(-1) at 1024 m and 58 dpm g sup(-1) to 588 dpm g sup(-1) at 3024 m. The mean annual sup(210)Pb flux increased from 0.27 dpm cm sup(-2) yr sup(-1) in the 1024 m trap to 0.65 dpm cm sup(-2) yr sup(-1) in the 3024 m trap. The sup(210)Pb flux exhibited a strong seasonal pattern associated with variations in the sediment mass flux and organic carbon (C sub(org)) flux except during early southwest monsoon in the 3024 m trap. This could be due to enhanced scavenging of sup(210)Pb on inorganic phases consisting mostly of Fe-Mn oxides. sup(210)Pb concentrations were dependent on particle composition, indicating that sup(210)Pb scavenging from the water column is directly coupled to the type of settling particles. Organic matter does not appear to be the dominant carrier phase for sup(210)Pb as shown by the poor sup(210)Pb-C sub(org) correlation. The fraction of sup(210)Pb removed from the ocean by settling particles F/P ( sup(210)Pb Flux / sup(210)Pb production) cannot be used as a proxy to determine the C sub(org) flux in this region. The excess sup(210)Pb inventories in 13 sediment cores in the Arabian Sea ranged from 11 to 211 dpm cm sup(-2). Such highly variable spatial distribution of the excess sup(210)Pb inventory reflects a non-uniform deposition of sup(210)Pb in this region. The measured excess sup(210)Pb inventories (124-211 dpm cm sup(-2)) for the sea floor sediments below the Western Arabian Sea Trap and from other locations in the vicinity of the sediment trap mooring lend support to boundary scavenging within the northwestern Arabian Sea as a sink for sup(210)Pb.
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