A model of the temporal and spatial distribution of carbon monoxide in the mixed layer

Abstract

A field experiment demonstrated the presence of a diurnal cycle in the concentration of carbon monoxide ([CO]) in the upper ocean at the BATS site. A series of laboratory experiments and numerical simulations were carried out to assess the diurnal variation in [CO] both at the sea surface and in the upper layers of the water column down to 200 m. Published studies of this cycle have suggested that the dominant controlling processes are light-induced production, microbial CO consumption, surface degassing, and dilution due to entrainment of deeper CO-depleted water into the mixed layer. Laboratory experiments focussed on finding the production rate coefficient and the destruction rate. The numerical studies were conducted to simulate the diurnal cycle in [CO] at the sea surface and at depth, and the results confirmed the values of the production rate coefficient and destruction rate obtained by the laboratory experiments. The field measurements indicate that [CO] does not vanish below the euphotic zone as expected. This may be due to a possible blank correction to the measurements, low destruction rate at depth, or a small dark production rate. The CO consumption e-folding was optimized by numeric experiment and calculated to be about 52±9 h on the basis of a minimized sea surface [CO] deviation and 73±10 h on the basis of minimized CO inventory deviation. Laboratory determinations of apparent quantum yield and numeric experiment lead to an optimized sea surface production of CO 0.40 ± 0.05nMh-1. Finally, deviations between the [CO] measurements and numeric experiments suggest that factors controlling the CO budget may be subject to spatial and temporal patchiness.