CHEMICAL ENHANCEMENT OF CO2 EXCHANGE IN NATURAL-WATERS

Exchange of CO2 under low turbulence conditions and high pH can be enh anced by hydration reactions of CO2 with hydroxide ions and water mole cules in the boundary layer. A series of held experiments was performe d on several lakes, including alkaline closed-basin lakes, using enclo sures (helmets) to study the enhancement process in nature. In additio n, the enhancement of CO2 exchange was studied in laboratory experimen ts with freshwater and seawater. The results of the experiments are co mpared with published theoretical calculations. Within the experimenta l uncertainties and shortcomings of the chemical enhancement models, r easonable agreement was observed between experimental and theoretical results for seawater. The experiments indicate, in accordance with the ory, that chemical enhancement has a minor effect on air-sea gas excha nge of CO2 under average oceanic turbulence conditions. However, for t he equatorial CO2 source regions, with high temperatures and low winds , the calculated CO2 enhancement amounts to 4-8% of the total exchange . The observations on lakes show poorer agreement with models, which i s attributed to experimental uncertainty and poor characterization of the chemistry of the lake waters. The experiments show that chemical e nhancement of CO2 is ubiquitous for the alkaline closed-basin lakes wi th enhancements of up to a factor of three.