Radiation and atmospheric circulation controls on carbonyl sulfide concentrations in the marine boundary layer

Abstract

AbstractA potential closure of the global carbonyl sulfide (COS or OCS) budget has recently been attained through a combination of remote sensing, modeling, and extended surface measurements. However, significant uncertainties in the spatial and temporal dynamics of the marine flux still persist. In order to isolate the terrestrial photosynthetic component of the global atmospheric OCS budget, tighter constraints on the marine flux are needed. We present 6 months of nearly continuous in situ OCS concentrations from the North Atlantic during the fall and winter of 2014–2015 using a combination of research vessel and fixed tower measurements. The data are characterized by synoptic‐scale ∼100 pmol mol−1 variations in marine boundary layer air during transitions from subtropical to midlatitude source regions. The synoptic OCS variability is shown here to be a linear function of the radiation history along an air parcel's trajectory with no apparent sensitivity to the chlorophyll concentration of the surface waters that the air mass interacted with. This latter observation contradicts expectations and suggests a simple radiation limitation for the combined direct and indirect marine OCS emissions. Because the concentration of OCS in the marine boundary layer is so strongly influenced by an air parcel's history, marine and atmospheric concentrations would rarely be near equilibrium and thus even if marine production rates are held constant at a given location, the ocean‐atmosphere flux would be sensitive to changes in atmospheric circulation alone. We hypothesize that changes in atmospheric circulation including latitudinal shifts in the storm tracks could affect the marine flux through this effect.