Global Model for Depth-Dependent Carbonyl Photochemical Production Rates in Seawater

A photochemical model was used to quantify the global contribution of carbonyl photoproduction in the photodegradation of marine dissolved organic carbon (DOC). As model input, wavelength- and temperature-dependent apparent quantum yields (AQYs) for the photochemical production of carbonyl compounds were determined in seawater collected from the Northwest Atlantic Ocean. These AQY data and published AQY data from the North Pacific were used with remotely sensed seawater optical properties and solar irradiance data in a global model to calculate depth-resolved, mixed-layer photochemical fluxes of acetaldehyde and glyoxal in seawater. Based on this model, the annual global surface mixed-layer photochemical production is 89.7 ± 36 Tg year⁻¹ for acetaldehyde and 20.0 ± 8.0 Tg year⁻¹ for glyoxal. This work significantly improves our understanding of the impact of photochemistry on the cycling of DOC in the surface oceans. Low-molecular-weight carbonyl compounds represent the second largest carbon flux among all known carbon products that are produced during the photolysis of DOC. The annual photoproduction of carbonyl-compound carbon is ~110 ± 23 Tg C year⁻¹, comprising approximately 9.6% of the total carbon and 22% of the biologically labile carbon that are produced globally from the photolysis of marine DOC.