COLLOIDAL ORGANIC-CARBON AND COLLOIDAL TH-234 DYNAMICS DURING A COASTAL PHYTOPLANKTON BLOOM

To investigate the association of Th-234 With organic colloids, colloidal Th-234 and colloidal organic carbon (COC) were measured during a coastal phytoplankton bloom. Bacterial and viral abundance were measured in addition to chlorophyll alpha so that changes in COC and Th-234 could be related to some basic microbial parameters during the course of the bloom. Two blooms, separated by a storm event, were observed at the 5 m sampling depth during the study. COC and colloidal Th-234 increased over the development of the first bloom, presumably due to the release of exudates by phytoplankton and the complexation of Th-234 with the exudates. Over the second bloom, Th-234 appeared to be tracking specific components of the COC and not the bulk COC. Exopolymers were not measured in this study; however, they were probably a major component of the phytoplankton exudates since the bloom was dominated by diatoms. It is proposed that exopolymers may play a significant role in the transfer of Th-234 from solution to particles and that the relative importance of exudate complexation and particles sorption to Th-234 transport needs to be determined.