Aquatic Sciences Meeting, Albuquerque 2001

PC15 Photochemistry

Date: Thursday, February 15, 2001

Location: Southwest Hall

Bouillon, R, C, Dalhousie University, Halifax, Canada, bouillon@is2.dal.ca

Miller, W, L, Dalhousie University, Halifax, Canada, william.miller@dal.ca

Levasseur, M, , Institut Maurice-Lamontagne, Mont-Joli, Canada, LevasseurM@dfo-mpo.gc.ca

THE SPECTRAL EFFICIENCY OF DIMETHYLSULFIDE (DMS) PHOTOLYSIS IN ESTUARINE WATERS.

Photochemical reactions can represent a major sink for DMS in the surface ocean. Unlike removal by microbial transformation and atmospheric ventilation, DMS photolysis in natural waters has not received much quantitative attention. There is currently only one published data set showing the spectral efficiency of this important removal process. In this study, laboratory irradiations were conducted to determine the apparent quantum yield (AQY) spectra of DMS photolysis using three different seawater samples from the St. Lawrence estuary (Canada). Samples in fifteen quartz cells were positioned within a water-thermostated, aluminum block, placed under sequential long-pass optical filters with distinct cutoffs from 280 to 480 nm, and exposed to radiation from a 1000 W xenon lamp. Using measured spectral irradiance, sample absorptivity, and measured DMS loss rates, AQY spectra for each irradiation experiment were calculated with a statistical fitting function. Photolysis efficiency increases exponentially from longer to shorter wavelengths. Interestingly, the AQY for stored seawater samples (>month) was significantly lower than that found for freshly collected sample. These results suggest that biologically labile DOM could play an important role in this photoreaction.

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Aquatic Sciences Meeting, Albuquerque 2001

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