Photochemical Production and Photolysis of Acrylate in Seawater.

Abstract

The marine organosulfur cycle has been studied intensively for over 30 years motivated by the hypothesis that dimethylsulfide (DMS) affects Earth's radiation balance and climate. The main source of DMS is from the enzymatic lysis of dimethylsulfoniopropionate (DMSP), the latter of which is a significant component of carbon, sulfur, and energy fluxes in the oceans. Acrylate is also produced during DMSP lysis, but unlike DMS or DMSP, very little is known about the marine acrylate cycle. Herein, a new source of acrylate was identified in seawater as a product formed from the photolysis of dissolved organic matter (DOM). Photochemical production rates varied from 1.6 to 5.0 pM (μmol quanta cm-2)-1, based on photon exposures determined from nitrite actinometry. A positive correlation (r = 0.87) was observed between acrylate photoproduction and the seawater absorption coefficient at 330 nm. Acrylate photoproduction was initiated by UV radiation, with UV-B and UV-A contributing approximately 32 and 68% to the total production, respectively. Acrylate did not photolyze in high-purity water or seawater at concentrations less than 100 nM. These findings improve our understanding of the role that sunlight plays in the marine acrylate cycle, a reactive form of DOM that significantly affects the carbon cycle and ecology of the upper ocean.