Microbial Controlled Carbon Monoxide Budget in the Marine Surface Waters

Abstract:

In the upper ocean, the dissolved CO exhibits typical diurnal cycle being produced by photolytic decomposition of chromophoric dissolved organic matter (CDOM), consumed by microbes, and outgassed by the gas exchange processes. To investigate the CO budget in the mixed layer, we measured air-sea gas exchange, microbial consumption rate, and CDOM on-board at two stark different marine environments in summer season of 2012: the Amundsen Sea, Antractica, and the North Pacific. Dark incubation experiments revealed that microbial consumption rate in the North Pacific was 4.5 nM d^-1 whilst 0.8 nM d^-1 in the Amundsen Sea. Also CO production rate was about 3.5-times higher in the North Pacific (2.4 nM d^-1) likely due to weak dilution and strong photochemical production. This different CO budget between the two regions renders different amplitude of diurnal variation of dissolved CO. That is, compared to the Amundsen Sea, CO was produced faster at daytime and removed faster at nighttime in the North Pacific where the amplitude of CO cycle is larger. In both regions, sea-to-air flux was insignificant (about 0.1 nM d^-1 for the both regions) and microbial consumption overwhelmed CO sinks. A simple mass-balance model simulated well our observations, suggesting that other processes than mentioned above were unrevealed.