title: Radiometric 81Kr dating identifies 120,000-year-old ice at Taylor Glacier, Antarctica.
abstract: We present successful (81)Kr-Kr radiometric dating of ancient polar ice. Krypton was extracted from the air bubbles in four ∼350-kg polar ice samples from Taylor Glacier in the McMurdo Dry Valleys, Antarctica, and dated using Atom Trap Trace Analysis (ATTA). The (81)Kr radiometric ages agree with independent age estimates obtained from stratigraphic dating techniques with a mean absolute age offset of 6 ± 2.5 ka. Our experimental methods and sampling strategy are validated by (i) (85)Kr and (39)Ar analyses that show the samples to be free of modern air contamination and (ii) air content measurements that show the ice did not experience gas loss. We estimate the error in the (81)Kr ages due to past geomagnetic variability to be below 3 ka. We show that ice from the previous interglacial period (Marine Isotope Stage 5e, 130-115 ka before present) can be found in abundance near the surface of Taylor Glacier. Our study paves the way for reliable radiometric dating of ancient ice in blue ice areas and margin sites where large samples are available, greatly enhancing their scientific value as archives of old ice and meteorites. At present, ATTA (81)Kr analysis requires a 40-80-kg ice sample; as sample requirements continue to decrease, (81)Kr dating of ice cores is a future possibility.
authors.affiliation: College of Earth, Ocean and Atmospheric Sciences, Oregon State University, Corvallis, OR 97331; buizertc@science.oregonstate.edu.
authors.forename: Christo
authors.initials: C
authors.lastname: Buizert
authors.affiliation: Scripps Institution of Oceanography, University of California, San Diego, CA 92093;
authors.forename: Daniel
authors.initials: D
authors.lastname: Baggenstos
authors.affiliation: Physics Division, Argonne National Laboratory, Argonne, IL 60439;
authors.forename: Wei
authors.initials: W
authors.lastname: Jiang
authors.affiliation: Climate and Environmental Physics, University of Bern, CH-3012 Bern, Switzerland;
authors.forename: Roland
authors.initials: R
authors.lastname: Purtschert
authors.affiliation: Department of Earth and Environmental Sciences, University of Rochester, Rochester, NY 14627;
authors.forename: Vasilii V
authors.initials: VV
authors.lastname: Petrenko
authors.affiliation: Physics Division, Argonne National Laboratory, Argonne, IL 60439;Department of Physics and Enrico Fermi Institute, University of Chicago, Chicago, IL 60637; and.
authors.forename: Zheng-Tian
authors.initials: ZT
authors.lastname: Lu
authors.affiliation: Physics Division, Argonne National Laboratory, Argonne, IL 60439;
authors.forename: Peter
authors.initials: P
authors.lastname: Müller
authors.affiliation: Ice Drilling Design and Operations, University of Wisconsin, Madison, WI 53706.
authors.forename: Tanner
authors.initials: T
authors.lastname: Kuhl
authors.affiliation: College of Earth, Ocean and Atmospheric Sciences, Oregon State University, Corvallis, OR 97331;
authors.forename: James
authors.initials: J
authors.lastname: Lee
authors.affiliation: Scripps Institution of Oceanography, University of California, San Diego, CA 92093;
authors.forename: Jeffrey P
authors.identifier: http://orcid.org/0000-0001-8883-3119
authors.initials: JP
authors.lastname: Severinghaus
authors.affiliation: College of Earth, Ocean and Atmospheric Sciences, Oregon State University, Corvallis, OR 97331;
authors.forename: Edward J
authors.initials: EJ
authors.lastname: Brook
mesh_terms: D000864:Antarctic Regions; D057231:Climate Change; D005740:Gases / Q000032:analysis; D007053:Ice / Q000032:analysis*; D046448:Ice Cover / Q000737:chemistry*; D007727:Krypton Radioisotopes; D055110:Radiometric Dating / Q000379:methods* / Q000592:standards; D015203:Reproducibility of Results
chemical_list: D005740:Gases; D007053:Ice; D007727:Krypton Radioisotopes
keywords: geochronology; glaciology; paleoclimatology
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