2003. Production and partitioning of organic matter during simulated phytoplankton blooms. Limnology and Oceanography 48:1,808–1,817

Few studies have examined the partitioning of organic matter in upwelling systems, despite the fact that these systems play a key role in carbon and nitrogen budgets in the ocean. We examined the production and partitioning of phytoplankton-derived organic matter in deck incubations off Oregon during the upwelling season. During ex-ponential growth of the phytoplankton, $78 % of total accumulated organic matter was in particulate (POM) form. This suggests that dissolved organic matter (DOM) is a small fraction of primary production during the exponential growth of coastal phytoplankton blooms. After nitrate depletion, carbon-rich (C: N $ 16) DOM accumulated in incubations dominated by the diatom Chaetoceros sp., accounting for 38 % (68.5%) of accumulated total organic carbon (TOC) and 24 % (68%) of accumulated total organic nitrogen (TON). However, in a bloom dominated by the diatom Leptocylindrus minimus, a relatively smaller amount of DOM accumulated, accounting for only 15 % of accumulated TOC and 7 % of accumulated TON. On the basis of measured concentrations of nitrate and accumulated TOC,;70%–157 % more carbon was fixed than would be predicted by Redfield stoichiometry (referred to as ‘‘excess carbon fixation’’), with 20%–69 % of the excess carbon fixation occurring after nitrate depletion. The accumulation of carbon-rich DOM and excess carbon fixation suggests that nitrate assimilation (i.e., new production) might not equate to net production of POM in coastal upwelling systems