Sediment trap experiments in the deep north Atlantic: isotopic and elemental fluxes

Sediment trap experiments have been carried out at sites in the Sargasso Sea (S/sub 2/) and in the Atlantic off Barbados (E) to determine the mass flux and chemical composition of material sinking to the sea floor. At the S/sub 2/ site, the mass flux increases with depth, at the E site the flux is constant. Chemical analyses show that K, Ti, Al, La, V, Co and /sup 232/Th are derived largely from terrigenous materials whereas Ca, Sr, Mg, Si, Ba, /sup 220/Ra, U and I are carried by biogenic particles. The reactive elements Mn, Cu, Fe, Sc, and /sup 230/ /sup 234/Th, show increasing ratios to Al with depth due to scavenging from the water column. A mean particle settling velocity of 21 m day/sup -1/ and scavenging residence times ranging from 22 years for Th to 500 years for Cu have been calculated. The flux of aluminosilicates increases with depth, and this cannot be attributed to changes in trap efficiency. Thus horizontal transport of material must be invoked.

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