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Open Access Publications from the University of California

Total Uncertainty of Radiocarbon Measurements of Marine Dissolved Organic Carbon and Methodological Recommendations

  • Author(s): Druffel, Ellen;
  • Griffin, Sheila;
  • Walker, B. D.;
  • Coppola, A. I.;
  • Glynn, D. S.
  • et al.

We report results of duplicate measurements of dissolved organic carbon concentrations ([DOC] as µM) and Δ14C in seawater in order to assess the total uncertainty of reported [DOC] and Δ14C measurements via the UV oxidation method. In addition, pure International Atomic Energy Agency standards analyzed over a 4-yr period are evaluated. We find the total uncertainty of Δ14C measurements to be ±4.0‰. However, in samples that were thawed, subsampled, and refrozen prior to UV oxidation, the total uncertainty of Δ14C measurements is on the order of ±10‰. The [DOC] measurements of these samples were also higher by 1.8 ± 0.3 µM. The reason(s) for these documented increases in total [DOC] and Δ14C uncertainty are unclear. In order to minimize any effects on sample measurements, we recommend the following: 1) regular monitoring of duplicate samples, DOC standards, and diluent (Milli-Q™) water for Δ14C and [DOC] measurements; 2) thawing a sample immediately and only once prior to UV oxidation; 3) avoid the use of DOC-leachable plumbing (such as PVC pipe) in both water systems feeding and within Milli-Q systems; and 4) consider the use of DOC-free diluents (i.e. pre-UV oxidized Milli-Q or sample water).

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