Photoproduction and Photolysis of Acrylate in Seawater

Lei Xue and David J Kieber, SUNY College of Environmental Science and Forestry, Department of Chemistry, Syracuse, NY, United States
The marine organosulfur cycle has received considerable attention since it was first proposed that dimethylsulfoniopropionate (DMSP), dimethylsulfide (DMS), and marine algae may affect the Earth's radiation balance and climate. It is evident from these studies that DMS(P) are quantitatively significant components of the carbon, sulfur, and energy flows in the oceans. By contrast, very little is known about acrylate concentrations, fluxes, or impacts in the oceans, even though it is produced during the conversion of DMSP to DMS, and its concentrations and fluxes should at times be substantial, especially in shallow-water coral reefs or during blooms of DMSP-rich phytoplankton that are common throughout the world's oceans and often harmful or toxic. Herein we show that acrylate is produced when 0.2-µm filtered seawater is exposed to sunlight, an abiotic production pathway for acrylate that has not been previously documented. Photochemical production rates varied from samples collected in the Atlantic and Pacific Oceans and the Gulf of Mexico, with a strong positive correlation observed between the photochemical production rate and initial absorption coefficient at 330 nm (r = 0.87). The concentration of acrylate increased in proportion to the decrease in the absorption coefficient at 330 nm, suggesting the involvement of CDOM in its photoproduction. No photolysis was observed in this study for acrylate in pure water or seawater in contrast to that reported in previous studies, presumably due to the rapid relaxation of triplet excited state by collision with water or energy transfer to dissolved oxygen in air-saturated seawater. These results will be discussed to assess the role of sunlight in the cycling of acrylate and carbon in the upper ocean.