NET COMMUNITY PRODUCTION OF DISSOLVED ORGANIC-CARBON

Each year large amounts of carbon, with a residence time of months, ac cumulate in the surface layer of the ocean as semilabile dissolved org anic carbon (DOC). This material is transported long distances, contri buting to the interhemispheric transfer and deep ocean export of carbo n. The fraction of net community production resulting in the accumulat ion of semilabile DOC is estimated here by mass balance during periods of net phytoplankton production in three diverse environments: the Ro ss Sea polynya, the Equatorial Pacific Ocean, and the Sargasso Sea. In the eutrophic systems of the Ross Sea and the Equatorial Pacific, net DOC production generally fell between 10 and 20% of net community pro duction. For the 1995 spring bloom in the Sargasso Sea, net DOC produc tion was 59-70% of the net community production. Net DOC production wa s maximal during the period of deep convective overturn of the water c olumn, indicating linkage between the processes. Following the Sargass o Sea spring bloom and into the summer period, net DOC production was nil over the upper 250 m so that net DOC production was reduced to sim ilar to 8% of net community production on a seasonal timescale. Consid eration of the various types of production regimes in the ocean indica tes that the global net production of semilabile DOC is similar to 17% of global new production. Regions of the world's oceans with the grea test contributions to global net community production, such as equator ial and coastal upwelling areas, contribute most to the global product ion of semilabile DOG.