Chromophoric Dissolved Organic Matter (CDOM) absorbs light at both ultraviolet and visible wavelengths. Due to its optical properties CDOM controls the quantity and quality of available light to phytoplankton in surface ocean waters. A fraction of CDOM emits the absorbed light as fluorescent radiation (FDOM). In marine systems, FDOM is a useful water mass tracer and an indicator of microbial and photochemical processes. FDOM in the oceans is imported from rivers and, mainly, produced in situ. While there are clear evidences that bacteria can produce FDOM, the role played by phytoplankton is still controversial. To add new information about the origin of marine FDOM, we performed incubation experiments with axenic cultures of four phytoplankton species of the genus Chaetoceros, Skeletonema, Prorocentrum and Micromonas. Our results showed that the four species produce fluorescent humic–like materials. The amount of produced FDOM varied depending on the species. The relevance of these findings for the utilization of FDOM as a tracer for biogeochemical processes in the oceans will be discussed

ASLO Aquatic Scicences Meeting, 25-30 January 2009, Nice (France)

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