Distribution, flux and photoproduction of carbon monoxide in the Bohai and Yellow Seas

•Bubble-mediated influence was considered in calculating the sea-to-air flux of CO.•The CO mixing ratios revealed the following order: the BS > the YS > the ECS in autumn.•Equation between the AQY and λ in the BS and YS was first presented in this study.•The total photomineralization rate of DOC was estimated in the BS and YS.

The distribution, sea-to-air flux, and photoproduction of carbon monoxide (CO) were determined in the Bohai Sea (BS) and the Yellow Sea (YS) during September, 2010. The concentrations of CO in the surface water varied from 0.09 to 6.81 nmol L− 1 with an average of 1.05 nmol L− 1. Surface water at most sampling stations was supersaturated with CO with a mean saturation factor of 2.3. The hourly and daily sea-to-air fluxes of CO were estimated to be 76.6 nmol m− 2 h− 1 and 0.65 μmol m− 2 d− 1, respectively. By extrapolation, the emission of CO from the study area accounted for 0.1% of the global oceanic emission. Coupled optical–photochemical modeling based on measured spectral CO apparent quantum yields arrived at a total CO photoproduction of 78.5 Gg CO-C yr− 1 in the study area. Using CO as a proxy for dissolved inorganic carbon and biolabile carbon photoproducts, the total photomineralization rate of dissolved organic matter was estimated to be 2.4 Tg C yr− 1, representing 2.0% of the primary production in the study area. Our results show that photomineralization is a relatively small but significant term in the organic carbon cycle of coastal waters.