A Primer on Dissolved Organic Material and Heterotrophic Prokaryotes in the Oceans

Abstract

Dissolved organic material (DOM) and microbes are well-recognized to be important components of carbon cycles and other biogeochemical cycles in the oceans. The main component of DOM, dissolved organic carbon (DOC), is one of the largest pools of carbon in the biosphere, equaling atmospheric CO2 in size (ca. 700 {\texttimes} 1015 tons) (Hedges and Oades 1997). The flux of carbon through the DOC pool is also substantial. Various approaches indicate that about 50% of primary production is some how routed through bacteria and single-cell eukaryotes (protists) that graze on bacteria, i.e. the microbial loop. Mineralization of DOM to CO2 and other inorganic nutrients by microbial loop microbes is one of three fates for primary production, the other two being grazing by protists and macrozooplankton (Fig. 1). In the open oceans, most of the carbon produced by phytoplankton (primary production) is mineralized by probst grazers or the microbial loop, leaving <10% for export to the deep ocean via sinking of large phytoplankton, the waste products (fecal pellets) of large zooplankton, or amorphorous aggregates of unclear origin. Carbon can also be exported as DOC in some oceanic regimes, as discussed below.