Grant Katherine E.

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Katherine E.

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  • Preprint
    Assessing the blank carbon contribution, isotope mass balance, and kinetic isotope fractionation of the Ramped Pyrolysis/Oxidation instrument at NOSAMS
    ( 2017-03) Hemingway, Jordon D. ; Galy, Valier ; Gagnon, Alan R. ; Grant, Katherine E. ; Rosengard, Sarah Z. ; Soulet, Guillaume ; Zigah, Prosper ; McNichol, Ann P.
    We estimate the blank carbon mass over the course of a typical Ramped PyrOx (RPO) analysis (150 to 1000 °C; 5 °C×min-1) to be (3.7 ± 0.6) μg C with an Fm value of 0.555 ± 0.042 and a δ13C value of (-29.0 ± 0.1) ‰ VPDB. Additionally, we provide equations for RPO Fm and δ13C blank corrections, including associated error propagation. By comparing RPO mass-weighted mean and independently measured bulk δ13C values for a compilation of environmental samples and standard reference materials (SRMs), we observe a small yet consistent 13C depletion within the RPO instrument (mean – bulk: μ = -0.8 ‰; ±1σ = 0.9 ‰; n = 66). In contrast, because they are fractionation-corrected by definition, mass-weighted mean Fm values accurately match bulk measurements (mean – bulk: μ = 0.005; ±1σ = 0.014; n = 36). Lastly, we show there exists no significant intra-sample δ13C variability across carbonate SRM peaks, indicating minimal mass-dependent kinetic isotope fractionation during RPO analysis. These data are best explained by a difference in activation energy between 13C- and 12C-containing compounds (13–12ΔE) of 0.3 to 1.8 J×mol-1, indicating that blank and mass-balance corrected RPO δ13C values accurately retain carbon source isotope signals to within 1 to 2‰.
  • Article
    Global patterns of radiocarbon depletion in subsoil linked to rock-derived organic carbon
    (European Association of Geochemistry, 2023-04-19) Grant, Katherine E. ; Hilton, Robert G. ; Galy, Valier V.
    Organic matter stored in sedimentary rocks is one of the largest stocks of carbon at Earth’s surface. The fate of this rock organic carbon (OCpetro) during weathering in soils influences the geological carbon cycle, and impacts soil radiocarbon content that is used to quantify soil carbon turnover. Here, we assess the potential contribution of OCpetro to soils, using a mixing model generated by a global dataset of soil radiocarbon measurements (14C). Soils developed on sedimentary rocks (rather than on igneous substrate) have a paired OC content and 14C values consistent with OCpetro input, giving rise to apparent increase in soil residence time. We call for renewed assessment of OCpetro input to soils, in terms of its impact on soil radiocarbon inventories, and its potential to release carbon dioxide.