OCE-9311383, PI-Sambrotto: In the Arabian Sea, as in other ocean regions, new production (that component of total nitrogen production fueled by nitrate and N2 fixation) is closely associated with the flux of organic material to deeper water. This flux is a crucial first step in the absorption of atmospheric C02 by the ocean, and in the Arabian Sea, is also associated with an extensive suboxic layer in which a singificant amount of denitrification occurs. In this project, new (nitrate) and regenerated (ammonium and urea) production will be measured with 15N tracer techniques during the low productivity spring transition period and again during the productive southeast monsoon. This provides an unusual opportunity to examine the seasonal development of elevated rates of new production that are not dominated by the steady improvement in the light field as they are in most high latitude systems. The biological nature of this transition will be evaluated by examing the light response of nitrate uptake as well as by post-incubation size fractionation experiments to determine if variations in new production and f-ratio are associated with changes in particle size distribution. Also, this project is designed to quantify the impact of new production on the carbon system experimentally during planned time series stations in which the 15N measurements can be compared to the changes determined by core measurements of the surface layer carbon system. This will test the nitrogen limited model of carbon consumption that is a crucial assumption in many estimates of carbon export.
