title: Methane seep carbonates yield clumped isotope signatures out of equilibrium with formation temperatures.
abstract: Methane cold seep systems typically exhibit extensive buildups of authigenic carbonate minerals, resulting from local increases in alkalinity driven by methane oxidation. Here, we demonstrate that modern seep authigenic carbonates exhibit anomalously low clumped isotope values (Δ47), as much as ∼0.2‰ lower than expected values. In modern seeps, this range of disequilibrium translates into apparent temperatures that are always warmer than ambient temperatures, by up to 50 °C. We examine various mechanisms that may induce disequilibrium behaviour in modern seep carbonates, and suggest that the observed values result from several factors including kinetic isotopic effects during methane oxidation, mixing of inorganic carbon pools, pH effects and rapid precipitation. Ancient seep carbonates studied here also exhibit potential disequilibrium signals. Ultimately, these findings indicate the predominance of disequilibrium clumped isotope behaviour in modern cold seep carbonates that must be considered when characterizing environmental conditions in both modern and ancient cold seep settings.
authors.affiliation: Department of Geological Sciences, California State University, Fullerton, California 92831, USA.|Department of Earth, Planetary and Space Sciences, University of California, Los Angeles, California 90095, USA.
authors.forename: S J
authors.initials: SJ
authors.lastname: Loyd
authors.affiliation: School of Earth Sciences and Environmental Sustainability, Northern Arizona University, Flagstaff, Arizona 86001, USA.
authors.forename: J
authors.initials: J
authors.lastname: Sample
authors.affiliation: Department of Earth, Planetary and Space Sciences, University of California, Los Angeles, California 90095, USA.|Department of Atmospheric and Oceanic Sciences, Institute of the Environment and Sustainability, University of California, Los Angeles, California 90095, USA.|European Institute of Marine Sciences (IUEM), Université de Brest, UMR 6538/6539, Rue Dumont D'Urville, and IFREMER, Plouzané 29019, France.
authors.forename: R E
authors.initials: RE
authors.lastname: Tripati
authors.affiliation: Department of Earth, Planetary and Space Sciences, University of California, Los Angeles, California 90095, USA.
authors.forename: W F
authors.initials: WF
authors.lastname: Defliese
authors.affiliation: Department of Earth, Planetary and Space Sciences, University of California, Los Angeles, California 90095, USA.
authors.forename: K
authors.initials: K
authors.lastname: Brooks
authors.affiliation: Centre for Geobiology, University of Bergen, Bergen 5003, Norway.
authors.forename: M
authors.initials: M
authors.lastname: Hovland
authors.affiliation: College of Earth, Ocean, and Atmospheric Sciences, Oregon State University, Corvallis, Oregon 97331, USA.
authors.forename: M
authors.initials: M
authors.lastname: Torres
authors.affiliation: Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125, USA.
authors.forename: J
authors.initials: J
authors.lastname: Marlow
authors.affiliation: Department of Earth Sciences, University of California, Riverside, California 92521, USA.
authors.forename: L G
authors.initials: LG
authors.lastname: Hancock
authors.affiliation: Department of Earth and Space Sciences/Burke Museum, University of Washington, Seattle, Washington 98195, USA.
authors.forename: R
authors.initials: R
authors.lastname: Martin
authors.affiliation: Department of Earth Sciences, University of California, Riverside, California 92521, USA.
authors.forename: T
authors.initials: T
authors.lastname: Lyons
authors.affiliation: Department of Earth, Planetary and Space Sciences, University of California, Los Angeles, California 90095, USA.|Department of Atmospheric and Oceanic Sciences, Institute of the Environment and Sustainability, University of California, Los Angeles, California 90095, USA.|European Institute of Marine Sciences (IUEM), Université de Brest, UMR 6538/6539, Rue Dumont D'Urville, and IFREMER, Plouzané 29019, France.
authors.forename: A E
authors.initials: AE
authors.lastname: Tripati