Carolyn D. Ruppel J. Southon John D. Kessler D.J. Joung 2022 <div id="ab0005" class="abstract author" lang="en"><div id="as0005"><p id="sp0030">Measurements of the natural radiocarbon content of methane (¹⁴C-CH₄) dissolved in seawater and freshwater have been used to investigate sources and dynamics of methane. However, during investigations along the Atlantic, Pacific, and Arctic Ocean Margins of the United States, as well as in the North American Great Lakes, some samples revealed highly elevated<span>&nbsp;</span>¹⁴C-CH₄<span>&nbsp;</span>values, as much as 4–5 times above contemporary atmospheric<span>&nbsp;</span>¹⁴C-CH₄<span>&nbsp;</span>levels. Natural production of the<span>&nbsp;</span>¹⁴CH₄<span>&nbsp;isotopologue is too low to cause these observations nor can it explain the variations in location and depth. Numerous lab and field validation tests and blanks, as well as the relatively small number of samples that display these elevated values, all suggest that these signals are not derived from an unknown procedural issue. Here we suggest that the byproducts of&nbsp;nuclear power generation&nbsp;include localized discharges of the&nbsp;</span>¹⁴CH₄<span>&nbsp;isotopologue into marine and&nbsp;aquatic environments, severely altering the measured&nbsp;</span>¹⁴C-CH₄<span>&nbsp;</span>isotopic signals. Since several of our sample sites are distant from on-land nuclear powerplants, we conduct further calculations concluding that the most elevated anomalies in<span>&nbsp;</span>¹⁴C-CH₄<span>&nbsp;</span>likely originate with discharge from nuclear-powered vessels.</p></div></div> application/pdf 10.1016/j.scitotenv.2021.150456 en Elsevier Elevated levels of radiocarbon in methane dissolved in seawater reveal likely local contamination from nuclear powered vessels article