Dynamic Cycle of Dissolved Organic Carbon and Marine Productivity

Dissolved organic matter (DOM) has an important role in ocean chemistry, in the remineralization of inorganic nutriens, feed web by heterotrophic organisms or as ligand of trace metals. Recent measurements of dissolved organic carbon (DOC) concentration in seawater using a high temperature catalytic oxidation (HTCO) method influenced strongly the biogeochemical ocean community. The HTCO method produced substantially higher values with more possibilities to be related to the consumption of oxygen. The first diel observations of DOC concentrations were done during the bloom study of JGOFS in 1989. DOC concentrations changed from 20 μM C to 50 μM C. This change is primarily due to the physical mixing of water and to biological processes. It was observed that there is a very weak negative correlation between the DOC inventory (0–50 m depth) and primary production. It seems that the rate of decomposition of DOC or DOM affects the rate of primary production. Using a two box model the DOM downward flux was calculated. It is likely that the DOM downward flux of about 5 GtC yr-1 plays an important role in the oceanic carbon cycle. The turnover time of DOC is calculated to be 2.9 years in the upper ocean layers and 170 years in the deep waters.