Global 3-D Model Analysis of the Seasonal Cycle of Atmospheric Carbonyl Sulfide: Implications for Terrestrial Vegetation Uptake

1 We use global 3-D atmospheric simulations of carbonyl sulfide (COS) to interpret 2 observations at a network of surface sites. We aim to identify the primary factors 3 underlying observed seasonal variations and to constrain COS uptake by terrestrial 4 vegetation. Model simulations based on a recent estimate of global COS fluxes (which 5 includes closure between sources and sinks) successfully represent observed variations in 6 southern high latitudes, providing support for the dominant influence of ocean fluxes 7 here. Simulations do not capture the amplitude of the observed seasonal cycle in the 8 northern hemisphere, indicating that COS uptake by terrestrial vegetation is 9 underestimated. A simulation with increased vegetation uptake (760 Gg S year, 10 increased by a factor of 3.2) provides the best fit to the observed seasonal variation in the 11 northern hemisphere. Balancing this sink requires a large COS source (420 Gg S y, 12 equivalent to 70% of identified sources) missing from present budget estimates. 13