Photochemical formation of glyoxylic and pyruvic acids in seawater

Abstract

Glyoxylic and pyruvic acids were formed when filter-sterilized seawater was exposed to solar radiation. Production rates varied from samples collected from distinctly different regions of the sea. Humic-rich seawater from the Florida Bay exhibited net photochemical production rates (glyoxylate, 27.5 nM/W-h m −2; pyruvate, 12.9 nM/W-h m −2) that were significantly greater than net production rates for humic-poor water (glyoxylate, 3.1 nM/W-h m −2; pyruvate, 1.8 nM/W-h m −2) collected in the Gulf Stream. When seawater was not filtered, the concentrations of glyoxylate and pyruvate were found to undergo diurnal variations resulting from an imbalance between biological and photochemical processes. A depth profile of the glyoxylate concentration from several oceanic stations showed a pronounced daytime maximum in the upper 10 m; this finding is consistent with laboratory results that demonstrated that glyoxylate is formed photochemically in seawater. Pyruvate, in contrast, showed no clear trend with depth; its distribution in the water column may be primarily controlled by biological processes rather than by photochemical processes. Biological processes are generally thought to control the spatial and temporal distribution of simple organic metabolites in seawater. Our results show that photochemical processes may also be important in the marine cycling of some biochemical compounds.