Particle Export Fields in the Arabian Sea Derived from 234TH: 238U Disequilibria

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9310702 Buesseler One of the major research objectives of the U.S.JGOFS Arabian Sea Process Study is measurement of the vertical and horizontal transport rates of particulate material, especially particulate organic carbon, in the Arabian Sea. Particle export from the surface layers of the ocean is of particular interest because that is the zone where new biological particles are formed, grazed, and physically altered, and then enter the decomposition cycle that regenerates dissolved nutrients. Although some investigators will be making such estimates by setting out open canisters at different depths and measuring the amount of material that collects in them over time, such efforts have a number of built-in uncertainties. The principal investigator of the present project, will approach the problem of estimating particle export from the surface ocean in a radically different way, on that will serve as an independent check on the sediment trap estimates. His approach takes advantage of the fact that the dissolved uranium in seawater decays to produce a radioactive daughter, thoraium- 234 (half-life-24 days), which (unlike the uranium) strongly attaches to particles. By sampling particles within and below the mixed upper water layer and measuring their TH-234 content and using some simple mathematical models, the investigator will be able to estimate particle from the mixed layer to depth. By measuring carbon and nitrogen contents of these materials, he will also be able to estimate fluxes of those two elements. A regional particulate carbon flux picture for the Arabian Sea region will be built up by using the data from some 25 stations collected during two monsoonal seasons (summer and winter) and two intermonsoonal periods. ***