234Th as a Tracer of Particulate C and N Export in the Equatorial Pacific

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The goal of this project is to use 234Th data to quantify the particulate flux of organic C and N at the base of the euphotic zone in the equatorial Pacific. Measurements of 234Th: 238U disequilibria in the spring and fall of 1992 will be used to quantify the particulate 234Th flux in north to south transects across the equator between 170 degrees W to 110 degrees W. The flux data will be combined with measurements of organic C/234Th and N/234Th ratios on size-fractionated particulate matter, to calculate the particulate flux of organic C and N. By taking advantage of shipboard gamma spectrometric analyses of 234Th, the flux data will be available in close-to-real time. Using an in- situ pumping system, all samples will be collected independent of other sampling activities. With this data set the equatorial Pacific's role in the global C budget for the removal of C and associated nutrients to the ocean's interior (new production) will be able to be quantified. In addition, the seasonal and spatial coverage will allow the extent to which new production is being exported as DOM rather than settling particles to be resolved, and the processes responsible for determining the efficiency of C export vs. recycling in the upper oceans will be better understood.