Timothy W. Hilton

Atmospheric carbonyl sulfide sources from anthropogenic activity: Implications for carbon cycle constraints

Carbonyl sulfide (COS) has recently emerged as an atmospheric tracer of gross primary production. All modeling studies of COS air-monitoring data rely on a climatological anthropogenic inventory that does not reflect present conditions or support interpretation of ice core and firn trends. Here we develop a global anthropogenic inventory for the years 1850 to 2013 based on new emission measurements and material-specific data. By applying methods from a recent regional inventory to global data, we find that the anthropogenic source is similar in magnitude to the plant sink, confounding carbon cycle applications. However, a material-specific approach results in a current anthropogenic source that is only one third of plant uptake and is concentrated in Asia, supporting carbon cycle applications of global air-monitoring data. Furthermore, changes in the anthropogenic source alone cannot explain the century-scale mixing ratio growth, which suggests that ice and firn data may provide the first global history of gross primary production.

Large variability in ecosystem models explains uncertainty in a critical parameter for quantifying GPP with carbonyl sulphide

Regional gross primary productivity (GPP) estimates are crucial to estimating carbon-climate feedbacks but are highly uncertain with existing methods. An emerging approach uses atmospheric carbonyl sulphide (COS) as a tracer for carbon dioxide: COS plant uptake is simulated by scaling GPP. A critical parameter for this method is leaf-scale relative uptake (LRU). Plant chamber and eddy covariance studies find a narrow range of LRU values but some atmospheric modelling studies assign values well outside this range. Here we study this discrepancy by conducting new regional chemical transport simulations for North America using the underlying data from previous studies. We find the wide range of ecosystem model GPP estimates can explain the discrepancy in LRU values. We also find that COS concentration uncertainty is more sensitive to GPP uncertainty than to LRU parameter uncertainty. These results support the COS tracer technique as a useful approach for constraining GPP estimates.

Assessing a New Clue to How Much Carbon Plants Take Up

Current climate models disagree on how much carbon dioxide land ecosystems take up for photosynthesis. Tracking the stronger carbonyl sulfide signal could help.

Plant Uptake of Atmospheric Carbonyl Sulfide in Coast Redwood Forests

Author(s): Campbell, JE; Whelan, ME; Berry, JA; Hilton, TW; Zumkehr, A; Stinecipher, J; Lu, Y; Kornfeld, A; Seibt, U; Dawson, TE; Montzka, SA; Baker, IT; Kulkarni, S; Wang, Y; Herndon, SC; Zahniser, MS; Commane, R; Loik, ME | Abstract: ©2017. American Geophysical Union. All Rights Reserved. The future resilience of coast redwoods (Sequoia sempervirens) is now of critical concern due to the detection of a 33% decline in California coastal fog over the 20th century. However, ecosystem-scale measurements of photosynthesis and stomatal conductance are challenging in coast redwood forests, making it difficult to anticipate the impacts of future changes in fog. To address this methodological problem, we explore coastal variations in atmospheric carbonyl sulfide (COS or OCS), which could potentially be used as a tracer of these ecosystem processes. We conducted atmospheric flask campaigns in coast redwood sites, sampling at surface heights and in the canopy (~70 m), at the University of California Landels-Hill Big Creek Reserve and Big Basin State Park. We simulated COS atmosphere-biosphere exchange with a high-resolution 3-D model to interpret these data. Flask measurements indicated a persistent daytime drawdown between the coast and the downwind forest (45 ± 6 ppt COS) that is consistent with the expected relationship between COS plant uptake, stomatal conductance, and gross primary production. Other sources and sinks of COS that could introduce noise to the COS tracer technique (soils, anthropogenic activity, nocturnal plant uptake, and surface hydrolysis on leaves) are likely to be small relative to daytime COS plant uptake. These results suggest that COS measurements may be useful for making ecosystem-scale estimates of carbon, water, and energy exchange in coast redwood forests.

Photosynthesis in high definition

Photosynthesis is the foundation for almost all known life, but quantifying it at scales above a single plant is difficult. A new satellite illuminates plants’ molecular machinery at much-improved spatial resolution, taking us one step closer to combined ‘inside–outside’ insights into large-scale photosynthesis.