A coupled model of the global cycles of carbonyl sulfide and CO₂: A possible new window on the carbon cycle

Abstract

[1] Carbonyl sulfide (COS) is an atmospheric trace gas that participates in some key reactions of the carbon cycle and thus holds great promise for studies of carbon cycle processes. Global monitoring networks and atmospheric sampling programs provide concurrent data on COS and CO 2 concentrations in the free troposphere and atmospheric boundary layer over vegetated areas. Here we present a modeling framework for interpreting these data and illustrate what COS measurements might tell us about carbon cycle processes. We implemented mechanistic and empirical descriptions of leaf and soil COS uptake into a global carbon cycle model (SiB 3) to obtain new estimates of the COS land flux. We then introduced these revised boundary conditions to an atmospheric transport model (Parameterized Chemical Transport Model) to simulate the variations in the concentration of COS and CO 2 in the global atmosphere. To balance the threefold increase in the global vegetation sink relative to the previous baseline estimate, we propose a new ocean COS source. Using a simple inversion approach, we optimized the latitudinal distribution of this ocean source and found that it is concentrated in the tropics. The new model is capable of reproducing the seasonal variation in atmospheric concentration at most background atmospheric sites. The model also reproduces the observed large vertical gradients in COS between the boundary layer and free troposphere. Using a simulation experiment, we demonstrate that comparing drawdown of CO 2 with COS could provide additional constraints on differential responses of photosynthesis and respiration to environmental forcing. The separation of these two distinct processes is essential to understand the carbon cycle components for improved prediction of future responses of the terrestrial biosphere to changing environmental conditions.

Fast retrievals of tropospheric carbonyl sulfide with IASI

“…A monthly mean of TES OCS results from June 2006 was published in Kuai et al (2015), which further validated the concept that direct ocean emissions of OCS are much greater than previously thought (Berry et al, 2013). The published data included retrievals over the ocean around ±40…”

“…Ingestion of OCS via leaf uptake only goes one way, meaning, plants do not respire OCS as they do unused CO 2 . Since OCS is roughly 4 times more variable than CO 2 , Berry et al (2013) suggested that remote detection of OCS could be used as a proxy towards estimating CO 2 fluxes over areas of dense vegetation. The remaining portion of the OCS sink budget is atmospheric loss due to reaction with the OH − and O − radicals along with stratospheric photolysis (Kettle et al, 2002).…”

Characterization of Aura TES carbonyl sulfide retrievals over ocean

“…It has a greenhouse gas effect based on absorption of far-infrared radiation (Brühl et al, 2012). OCS is also found as a potential trace gas, other than carbon dioxide, that could provide independent information about carbon cycle processes (Montzka et al, 2007;Campbell et al, 2008;Suntharalingam et al, 2008;Wohlfahrt et al, 2012;Blonquist et al, 2011;Berry et al, 2013). For example, recent work by Campbell et al (2008) suggests that carbonyl sulfide is a good photosynthetic tracer.…”

Seasonal fluxes of carbonyl sulfide in a midlatitude forest

“…Studies considering the large-scale atmospheric variability of OCS have linked OCS fluxes and the photosynthetic uptake of CO 2 for regional and global scales (1,4,13). Leaf-scale studies have confirmed the OCS link to photosynthesis (14,15).…”

“…7 and 8). The terrestrial biosphere is the largest sink for OCS (1,4,9,10) with uptake by both oxic soils (e.g., ref. 11) and vegetation (e.g., ref.…”