In situ production of dissolved organic carbon (DOC) by phytoplankton blooms (Cochlodinium polykrikoides) in the southern sea of Korea

We measured dissolved organic carbon (DOC) concentration in the surface seawater of Gamak Bay located in the southern Korea and groundwater nearby the bay in August 2007 to determine effect of harmful algal blooms on DOC distribution in the surface waters. The average of DOC concentration in the bloom stations (157 ± 25 μM) was 1.6-fold higher than that of the non-bloom stations (96 ± 15 μM). The DOC concentrations in groundwater and offshore seawater were significantly lower than those in the bloom stations but showed similar values in the non-bloom stations. The facts that salinity showed no significant relationship with DOC but Chl-a showed a significant correlation with DOC, indicate that the major source of DOC in the bloom stations may be in situ phytoplankton production rather than groundwater and/or river water. In addition, DOC showed a strong relationship with peridinin (biomarker of dinoflagellate) but showed no relationship with fucoxanthin (biomarker of diatom). These results suggest that the DOC distribution in Gamak Bay seems to be controlled by in situ phytoplankton production by dinoflagellate rather than diatom. Therefore, distributions of DOC in the southern sea of Korea during bloom season may be controlled by biological processes such as the intensity and duration of dinoflagellate.