Distribution and cycling of carbon monoxide in the east china sea and the marine atmosphere in autumn

Abstract

Carbon monoxide (CO) concentrations, sea-to-air fluxes and microbial consumption rate constants, along with atmospheric CO mixing ratios, were measured in the East China Sea (ECS) in autumn. Atmospheric CO mixing ratios varied from 96 to 256 ppbv, with an average of 146 ppbv (SD = 54 ppbv, n = 31). Overall, the atmospheric CO concentrations displayed a decreasing trend from inshore to offshore stations. The surface water CO concentrations in the investigated area ranged from 0.24 to 6.12 nmol L⁻¹, with an average of 1.68 nmol L⁻¹ (SD = 1.50 nmol L⁻¹, n = 31). The surface water CO concentrations were affected significantly by sunlight. Vertical profiles showed that CO concentrations declined rapidly with depth, with the maximum appearing in the surface water. The surface CO concentrations were oversaturated, with the saturation factors ranging from 1.4 to 56.9, suggesting that the ECS was a net source of atmospheric CO. The sea-to-air fluxes of CO in the ECS ranged from 0.06 to 11.31 µmol m⁻² d⁻¹, with an average of 2.90 µmol m⁻² d⁻¹ (SD = 2.95µmol m⁻² d⁻¹, n = 31). In the incubation experiments, CO concentrations decreased exponentially with incubation time and the processes conformed to the first order reaction characteristics. The microbial CO consumption rate constants in the surface water (K_CO) ranged from 0.063 to 0.22 h⁻¹, with an average of 0.12 h⁻¹ (SD = 0.062 h⁻¹, n = 6). A negative correlation between K_CO and salinity was observed in the present study.