title: Isotope geochemistry. Biological signatures in clumped isotopes of O₂.
abstract: The abundances of molecules containing more than one rare isotope have been applied broadly to determine formation temperatures of natural materials. These applications of "clumped" isotopes rely on the assumption that isotope-exchange equilibrium is reached, or at least approached, during the formation of those materials. In a closed-system terrarium experiment, we demonstrate that biological oxygen (O2) cycling drives the clumped-isotope composition of O2 away from isotopic equilibrium. Our model of the system suggests that unique biological signatures are present in clumped isotopes of O2—and not formation temperatures. Photosynthetic O2 is depleted in (18)O(18)O and (17)O(18)O relative to a stochastic distribution of isotopes, unlike at equilibrium, where heavy-isotope pairs are enriched. Similar signatures may be widespread in nature, offering new tracers of biological and geochemical cycling.
authors.affiliation: Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, CA 90095, USA. Department of Earth Science, Rice University, Houston, TX 77005, USA. lyeung@rice.edu jlash@ucla.edu.
authors.forename: Laurence Y
authors.initials: LY
authors.lastname: Yeung
authors.affiliation: Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, CA 90095, USA. lyeung@rice.edu jlash@ucla.edu.
authors.forename: Jeanine L
authors.initials: JL
authors.lastname: Ash
authors.affiliation: Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, CA 90095, USA.
authors.forename: Edward D
authors.initials: ED
authors.lastname: Young
mesh_terms: D031423:Hyacinthus / Q000737:chemistry / Q000378:metabolism; D010100:Oxygen / Q000737:chemistry* / Q000378:metabolism; D010103:Oxygen Isotopes / Q000032:analysis / Q000737:chemistry; D010788:Photosynthesis; D045332:Photosystem II Protein Complex / Q000737:chemistry; D013269:Stochastic Processes; D013696:Temperature; D014867:Water / Q000737:chemistry
chemical_list: D010103:Oxygen Isotopes; D045332:Photosystem II Protein Complex; D014867:Water; D010100:Oxygen