Danielle S. Gruen Barbara Sherwood Lollar Kai-Uwe Hinrichs Lucy C. Stewart James F. Holden Alexander N. Hristov John W. Pohlman Penny L. Morrill Martin Konneke Kyle B. Delwiche Eoghan P. Reeves Chelsea N. Sutcliffe Daniel J. Ritter Jeffrey S. Seewald Jennifer C. McIntosh Harold F. Hemond Michael D. Kubo Dawn Cardace Tori M. Hoehler Shuhei Ono David T. Wang 2015 <p><span>Methane is a key component in the global carbon cycle with a wide range of anthropogenic and natural sources. Although isotopic compositions of methane have traditionally aided source identification, the abundance of its multiply-substituted &ldquo;clumped&rdquo; isotopologues, e.g.,<span class="Apple-converted-space">&nbsp;</span></span>¹³<span>CH</span>₃<span>D, has recently emerged as a proxy for determining methane-formation temperatures; however, the impact of biological processes on methane&rsquo;s clumped isotopologue signature is poorly constrained. We show that methanogenesis proceeding at relatively high rates in cattle, surface environments, and laboratory cultures exerts kinetic control on<span class="Apple-converted-space">&nbsp;</span></span>¹³<span>CH</span>₃<span>D abundances and results in anomalously elevated formation temperature estimates. We demonstrate quantitatively that H</span>₂<span><span class="Apple-converted-space">&nbsp;</span>availability accounts for this effect. Clumped methane thermometry can therefore provide constraints on the generation of methane in diverse settings, including continental serpentinization sites and ancient, deep groundwaters.</span></p> application/pdf 10.1126/science.aaa4326 en American Association for the Advancement of Science Nonequilibrium clumped isotope signals in microbial methane article