Radionuclide fluxes and particle scavenging in Cariaco Basin

摘要

Th-234, Th-228 and Pb-210 fluxes were measured in a series of sediment trap samples in Cariaco Basin from November 1995 to 8 May 1996. Sediment traps were located at 275, 455, 930 and 1255 m depth, with the 275 m trap just above the oxic/anoxic interface. Total mass, organic carbon, carbonate, biogenic opal, and lithogenic fluxes were also determined. Our results found that Th-234, Th-228 and Pb-210 fluxes are highly correlated with total mass (r(2) = 0.92 - 0.94), major sediment component fluxes (r(2) = 0.82 - 0.93), and one another (r(2) = 0.94 - 0.99). Decreases in radionuclide, total mass and major sediment component fluxes with depth were attributed to physical disaggregation and remineralization. While the Pb-210 specific activity loss from settling particles is the same as the bulk specific activity of the trapped particles between (455) and (930)m, the Pb-210 specific activity loss is substantially higher than the bulk specific activity of the trapped particles between 930 and 1255m. We attributed this fractionation to a loss of minor components from settling particles. This suggests that minor components are responsible for the initial water column scavenging of Pb-210 in the Cariaco Basin. Steady state release of Pb-210 from settling particles would produce an anoxic water column activity an order of magnitude greater than previously reported. Therefore, a non-steady state removal mechanism must exist and is potentially caused by high sediment flux events from earthquake triggered turbidity currents or major plankton blooms.(C) 2004 Elsevier Ltd. All rights reserved.