Scholten, J. C., Fietzke, Jan , Vogler, S., van der Loeff, M. M. R., Mangini, A., Koeve, W., Waniek, J., Stoffers, Peter, Antia, A. and Kuss, J. (2001) Trapping efficiencies of sediment traps from the deep Eastern North Atlantic: the (230)Th calibration. Deep-Sea Research Part Ii-Topical Studies in Oceanography, 48 (10). pp. 2383-2408. DOI 10.1016/s0967-0645(00)00176-4.

Abstract

Bottom-tethered sediment traps deployed in the deep eastern North Atlantic between 54 degreesN 20 degreesW and 33 degreesN 20 degreesW (L1, L2, L3), at the European continental margin at 49 degreesN (OMEX) and off the Canary Islands (ESTOC) were investigated for the determination of (230)Th trapping efficiencies. The ratios of (230)Th flux measured in the traps (Fa) to the expected (230)Th flux from the production rate of (230)Th in the overlying water column (Fp) ranged between 0.09 and 1.26. For the traps with deployment periods > 300 days the interannual variation of Fa/Fp ratios (different years but same location and water depth) were up to 10%, suggesting that the average (230)Th flux to the sediment traps did not vary significantly. The influence of lateral advection on the (230)Th flux was taken into account either by applying a mass balance of (230)Th and (231)Pa or by assuming a constant removal rate of (230)Th from the water column, an assumption based on similar (230)Th concentration-depth profiles observed at most locations investigated. (230)Th trapping efficiencies were between 9 and 143 %, showing a trend of increasing efficiencies with increasing water depth. No relation was found between current velocities and (230)Th trapping efficiencies. Our investigations suggest that the observation of constant or even increasing particle flux rates with increasing water depths in several sediment trap arrays investigated may be a result of sediment trap biases. The correction for the trapping biases is important for the understanding of the regional differences in the particle flux in the eastern North Atlantic. (C) 2001 Elsevier Science Ltd. All rights reserved.

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