Effects of nutrient deficiency on the CH2I2, CH2ClI, and CH2BrI production in cultures of the temperate marine phytoplankton Bigelowiella natans

Volatile organic iodine compounds (VOICs) such as di-iodomethane (CH2I2) released from the ocean are important vectors of iodine in the atmosphere and play an important role in atmospheric chemistry. In temperate ocean waters, several studies observed or presumed CH2I2 production. Here, we investigated the ability of temperate marine phytoplankton to produce VOICs in a culture experiment. To evaluate the decrease of 13CH2I2 by photolysis and release during sampling, we also performed an incubation experiment involving the addition of 13CH2I2 to the f/2-Si medium. Axenic cultures of B. natans in f/2-Si medium showed no production of CH2I2, but axenic cultures of B. natans in phosphorus-deficient cultures and nitrogen-deficient cultures exhibited remarkable rates of CH2I2 production: 5.3–5.9 pmol (μg chlorophyll a)−1 d−1 and 0.8–1.3 pmol (μg chlorophyll a)−1 d−1, respectively. Similarly, the production of chloroiodomethane (CH2ClI) and bromoiodomethane (CH2BrI) was observed in phosphorus- or nitrogen-deficient cultures, but not in f/2-Si culture. Higher production rates of CH2I2, CH2ClI, and CH2BrI were observed during the early exponential phase of B. natans cultures. The relative concentration ratio of CH2I2, CH2ClI, and CH2BrI in the B. natans cultures were approximately 70:8:1 and 15:10:1 in the phosphorus-deficient and nitrogen-deficient cultures, respectively. Based on the results of the addition of 13CH2I2 in a culture experiment, we estimated that CH2I2 was decreased by approximately 8.6% due to photolysis and volatilization during the fifth and tenth day, during which time CH2I2 production was observed in B. natans cultures in f/2-Si with a half-concentration of phosphorus. These results suggested that a nutrient deficiency could induce the production of VOICs derived from temperate marine phytoplankton such as B. natans and that nutritional conditions are one of the important factors for the estimation of VOIC emissions from temperate open ocean.