Net community production of dissolved organic carbon

Abstract

Each year large amounts of carbon, with a residence time of months, accumulate in the surface layer of the ocean as semilabile dissolved organic carbon (DOC). This material is transported long distances, contributing to the interhemispheric transfer and deep ocean export of carbon. The fraction of net community production resulting in the accumulation of semilabile DOC is estimated here by mass balance during periods of net phytoplankton production in three diverse environments: the Ross 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 production. For the 1995 spring bloom in the Sargasso Sea, net DOC production was 59‐70% of the net community production. Net DOC production was maximal during the period of deep convective overturn of the water column, indicating linkage between the processes. Following the Sargasso 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 ∼8% of net community production on a seasonal timescale. Consideration of the various types of production regimes in the ocean indicates that the global net production of semilabile DOC is ∼17% of global new production. Regions of the world's oceans with the greatest contributions to global net community production, such as equatorial and coastal upwelling areas, contribute most to the global production of semilabile DOC.