Responses of carbon monoxide photoproduction in surface seawater to environmental changes under simulated solar radiation

The ocean is undergoing rapid environmental changes, but how carbon monoxide (CO) photoproduction responds to these changes remains uncertain. Therefore, we used simulated solar radiation to investigate the effects of ocean warming, acidification, deoxygenation, and nitrate concentration changes on CO photoproduction rate in the surface seawater of the Yellow Sea (YS), the East China Sea (ECS), the South China Sea (SCS), and the eastern Indian Ocean (EIO). Ultraviolet radiation contributed more than 90% to CO photoproduction. Dissolved organic matter (DOM) with high aromaticity and abundant humic-like component was an important precursor for CO photoproduction. Under the high-emission scenario, warming is projected to significantly enhance CO photoproduction rate by ∼15% in the terrestrial-influenced regions of the YS and ECS by 2100. In contrast, its effect is projected to be insignificant (an increase of ∼8%) in the oligotrophic SCS and EIO. Moreover, neither a pH reduction of 0.2 or 0.4 units nor deoxygenation are expected to have significant influence on CO photoproduction rate in the study areas. CO photoproduction increases with increasing nitrate concentration, which is attributed to hydroxyl radicals (•OH) produced by nitrate photolysis. The •OH generated by natural seawater photolysis in the investigated areas induced about 10%–23% of CO photoproduction.