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210Pb in the sediments and water column of the Northeast Atlantic from 47 to 59°N along 20°W

Earth and Planetary Science Letters
Publication Date
DOI: 10.1016/0012-821x(93)90214-t


Abstract Over much of the deep North Atlantic Ocean the water column and atmospheric input deficit of the radionuclide 210Pb is not matched by the inventories found in the underlying sediments. This implies that an unidentified extensive or intense sink (or sinks) for 210Pb must exist in the Atlantic to counterbalance the large area of open ocean in deficit. One likely sink area which has been suggested is the Atlantic north of 50°N, because of its moderately high surface productivity and the high inventories observed in the limited number of cores available. This work tests the hypothesis by investigating the water column at 48°N, 20°W and a set of cores from 47 to 59°N along 20°W. The water column deficit is 21 dpm 210Pb·cm −2 in a water column of 4500 m depth and a 226Ra content of 54 dpm·cm −2. The important unmeasured parameter is the atmospheric input of 210Pb to the surface ocean, but the 100 yr average fluxes for the majority of the cores (eight out of eleven) can be modelled to within ±40% of their observed values with a value of 0.30 dpm·cm −2·y −1 for the atmospheric input added to the flux implied by the water column deficit. This leads to best-estimate values of the characteristic water column parameters scavenging effectiveness and τ scav of 48% and 35 yrs, respectively, which are typical North Atlantic values. It is concluded that removal from the water column and steady-state supply to the sediments are in approximate balance along this transect, and that this part of the North Atlantic is not a preferential sink for 210Pb. Two cores from a sediment drift area do show active enhanced 210Pb excess accumulation, but this is ascribed to current-driven fine sediment redistribution rather than to productivity-driven enhanced removal from the water column.

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