Soil carbonyl sulfide (OCS) fluxes in terrestrial ecosystems: An empirical model

Whelan, M.E.; Shi, Mingjie; Sun, Wu; Vries, Linda Kooijmans‐de; Seibt, Ulli and Maseyk, Kadmiel (2022). Soil carbonyl sulfide (OCS) fluxes in terrestrial ecosystems: An empirical model. Journal of Geophysical Research: Biogeosciences, 127, article no. e2022JG006858.



Measurements of carbonyl sulfide (OCS) enable independent estimates of regional stomatal conductance provided that non-stomatal OCS fluxes are well constrained. OCS is taken up through plant leaves, following the same pathway as CO2; in contrast to CO2, OCS is irreversibly destroyed in plant leaves and plants do not typically exhibit OCS emissions. Ecosystem uptake of OCS can indicate changes in stomatal opening. Here we present an empirical model to assess the potential impact of soil OCS exchange, the non-Stomatal OCS exchange Empirical Model (SOCSEM, version 0). We created biome-specific response curves characterizing soil OCS exchange and restricted the model design to require only knowledge of soil moisture and surface temperature because remote sensing observations are available for these two features. Comparing the model to field-based chamber observations reveal deviations that can be attributed to missing complexity of the ground surface (having excluded litter and plants without regulated stomata), shortwave radiation, or the soil environment. For agricultural regions with known net emissions, we use remotely-sensed surface temperature data and demonstrate that data resolution can affect the sign of anticipated fluxes. We further investigate the influence of regions with unknown soil OCS responses, e.g. Arctic tundra. We compare our model to a process-based and respiration-based soil OCS exchange model that has been implemented in a land surface model. Further field study of tropical and arctic ecosystems in conjunction with studies of non-stomatal surfaces in addition to soil (e.g. bryophytes) will increase confidence in applying OCS as a regional tracer for stomatal conductance.

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