Carbonyl sulfide (OCS) has gained prominence as an independent tracer for gross primary productivity, which is usually modelled by partitioning net CO₂ fluxes. Here, we present a simple empirical model for estimating ecosystem-scale OCS fluxes for a temperate old-growth forest and find that OCS sink strength scales with independently estimated CO₂ uptake and is sensitive to the the fraction of downwelling diffuse light. We also examine the response of OCS and CO₂ fluxes to sequential heat waves.