Distributions, sea-to-air fluxes, and biological consumption of carbon monoxide in the Bohai and Yellow Seas during winter

Carbon monoxide (CO) concentrations in the atmosphere and ocean are mainly influenced by anthropogenic inputs, abiotic photoproduction, biogenic sources, and bacterial consumption. This study, for the first time, investigated the distributions, sea-to-air fluxes, and microbial consumption rates of CO in the Bohai Sea (BS) and the Yellow Sea (YS) in winter to identify the main factors controlling CO distributions in both the atmosphere and seawater in colder temperature. Atmospheric CO mixing ratios ([CO]_atm) and the concentrations of CO in surface seawater ([CO]_surf) ranged from 176.8 to 1245.8 ppbv (mean value: 551.4 ± 214 ppbv) and from 0.49 to 3.1 nmol L⁻¹ (mean value: 0.98 ± 0.55 nmol L⁻¹), respectively. In addition, the spatial distribution of [CO]_atm and [CO]_surf showed that anthropogenic sources dominated the distribution of [CO]_atm, but abiotic photoproduction processes were the main influencers of the distribution of [CO]_surf. The surface water at most sampling stations was supersaturated with CO, with a mean saturation factor of 1.9, and the sea-to-air fluxes of CO were estimated to range from −13.88 to 123.88 nmol m⁻² h⁻¹ (12.59 ± 21.32 nmol m⁻² h⁻¹), suggesting that the BS and the YS were the source of atmospheric CO,  and were estimated to contribute 0.009% to 1.4% to the global ocean emission. Microbial consumption experiments indicated that the microbial CO consumption rate constants (K_bio) ranged from 0.15 to 2.14 h⁻¹, and showed that CO concentrations decreased exponentially with incubation time, suggesting that anaerobic CO consumption would limit CO accumulation in winter, thereby affecting the flux of [CO]_surf to [CO]_atm.