Chemical fluxes from a sediment trap experiment in the deep Sargasso Sea

Abstract

A pair of sediment traps, each with an opening of 1.5 m/sup 2/, were deployed at 5367m in 5581m of water at 31/sup 0/ 34'N, 55/sup 0/ 03'W in the Sargasso Sea. The traps were located within the bottom nepheloid layer, which, at this site, extends from about 4900m to the bottom. The two traps collected different amounts of material, one collecting 3.45g, and the other 6.90g. The difference is probably attributable to mooring and shadow effects, and may be a general problem for this class of experiment. In a collection time of 75 days, the mean total particulate flux is estimated to be 1.68 +- 0.79 mg cm/sup -2/y/sup -1/. Samples from each trap have been analyzed for the elements Si, Al, Ca, K, Mg, Fe, Mn, Ba, Sr, Ti, V, I, Sc, La, Cr, Sb, Cu, Zn, Cd, Ni and Co by a combinationof instrumental neutron activation and atomic absorption techniques. Several radioisotopes, including /sup 234/Th, /sup 228/Th, /sup 230/Th, /sup 232/Th, /sup 210/Po, /sup 210/Pb, /sup 227/Th, /sup 238/U, and /sup 226/Ra, have been determined by ..cap alpha.. and ..beta.. spectrometry. The trapped material consists of about 50% clay, 20% calcium carbonate, 20% silica and 5% organic matter. In interpreting these data, we have paid particular attention to the following problems: separation of the primary flux from the re-suspended sediment contribution, estimation of the trap efficiency for different size classes of particles, estimation of particle settling velocities and assessment of adsorption onto particles during transit through the water column. These problems are common to most sediment trap experiments.