Abstract
Abstract. Carbonyl sulfide (OCS) has recently emerged as a tracer for terrestrial carbon uptake. While physiological studies relating OCS fluxes to leaf stomatal dynamics have been established at leaf and branch scales and incorporated into global carbon cycle models, the quantity of data from ecosystem-scale field studies remains limited. In this study, we employ established theoretical relationships to infer ecosystem-scale plant OCS uptake from mixing ratio measurements. OCS fluxes showed a pronounced diurnal cycle, with maximum uptake at midday. OCS uptake was found to scale with independent measurements of CO2 fluxes over a 60 m tall old-growth forest in the Pacific Northwest of the US (45∘49′13.76′′ N, 121∘57′06.88′′ W) at daily and monthly timescales under mid–high light conditions across the growing season in 2015. OCS fluxes were strongly influenced by the fraction of downwelling diffuse light. Finally, we examine the effect of sequential heat waves on fluxes of OCS, CO2, and H2O. Our results bolster previous evidence that ecosystem OCS uptake is strongly related to stomatal dynamics, and measuring this gas improves constraints on estimating photosynthetic rates at the ecosystem scale.
Highlights
Carbonyl sulfide (OCS) is the most abundant sulfur gas in the atmosphere, with a mean atmospheric concentration of ∼ 500 ppt, and a significant part of the tropospheric and stratospheric sulfur cycles, with implications for the global radiation budget and ozone depletion (Johnson et al.,1993; Notholt et al, 2003)
Recent advances in spectroscopic technology have enabled continuous in situ measurements of OCS on timescales that are relevant to understanding stomatal function at the leafscale (Stimler et al, 2010a, b), branch scale (Berkelhammer et al, 2014), and the ecosystem scale (Kooijmans et al, 2017; Wehr et al, 2017)
The total ecosystem flux of OCS (FOCS; Fig. 2d) follows a pronounced diurnal cycle that peaks at midday
Summary
Carbonyl sulfide (OCS) is the most abundant sulfur gas in the atmosphere, with a mean atmospheric concentration of ∼ 500 ppt (parts per trillion), and a significant part of the tropospheric and stratospheric sulfur cycles, with implications for the global radiation budget and ozone depletion (Johnson et al.,1993; Notholt et al, 2003). Both uptake and emissions of OCS from soils have been identified (Whelan et al, 2016; Sun et al, 2015; Maseyk et al, 2014; Kesselmier et al, 1999). While ecosystem-scale measurements of OCS continue to establish links between OCS uptake and GPP in different ecosystems (for a comprehensive list of ecosystemscale studies, readers are referred to Fig. 2 in Whelan et al, 2018), inconsistencies persist. Uncertainties highlighted above argue for fieldscale measurements of OCS in a variety of ecosystems, as OCS flux predictions have recently been incorporated to inform estimates of plant productivity in global carbon cycle models (Campbell et al, 2017a; Hilton et al, 2017; Launois et al, 2015)
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