Carbonyl sulfide (COS) is a trace gas used as a proxy for photosynthesis, and plants take up COS just like CO2 but do not emit back respiration. COS has been measured from Hyytiala during 2013-17 and then 2020-2022. This is the longest COS eddy covariance flux measurement from a boreal forest. Following the forest thinning in the winter of 2019–2020, COS fluxes were altered; A reduction in uptake was observed in 2020 and then anomalous emissions in the summer of 2021. For the first time, extended periods of ecosystem-scale COS emissions were observed in a boreal forest. The analysis suggests an unidentified, homogeneously distributed COS source in the area, potentially from the photodegradation of forest floor litter and cutting residue from thinning.
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