The Contribution of Boreal Wetlands to the Northern Hemisphere Carbonyl Sulfide Sink

Carbonyl sulfide (COS), a gas used as a tracer in carbon cycle studies, has a potential missing sink in Northern high latitudes. Boreal COS budgets typically account for the contribution by forests, but ignore any uptake that wetland ecosystems, widespread in Northern latitudes, may contribute. The first direct measurements of the ecosystem-atmosphere COS exchange of a boreal wetland, presented here, demonstrate their likely importance for Northern latitude COS budgets. The investigated wetland (Siikaneva, Finland) took up on average 11 pmol m⁻² s⁻¹ COS, which was c. 72% of the nearby boreal forest COS uptake. During nighttime, the COS uptake rates were similar at both sites. Upscaling our measurements to the boreal region using the Organizing Carbon and Hydrology In Dynamic Ecosystems model revealed a Northern wetland sink of c. 13 Gg S/y, changing the simulated budget from a small source to a COS sink impacting Northern latitudes carbon uptake estimates based on COS.