Nutrient limitation in two marine diatoms inhibits release of bromoform

Bromoform released from phytoplankton and kelp in the ocean is the largest known carrier of bromine to the atmosphere. The photoproducts of atmospheric bromoform catalyse ozone depletion. Laboratory investigations were conducted into the link between nutrient limitation and bromoform production using axenic cultures of two warm-water diatoms (Chaetoceros neogracile and Phaeodactylum tricornutum). During exponential growth the bromoform production was 2 000–3 000 nmol bromoform (g Chl a)−1 h−1, i.e. 10–100 times higher than earlier values for temperate and cold-water diatoms. Bromoform production decreased down to zero under CO2 and nitrate limitation for both species. These results suggest that the bromoform production could be directly related to bromoperoxidase activity (and irradiance) only during exponential growth, whereas compounds other than bromoform might be formed under nutrient limitation.