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. 2014 May 13;111(19):6876-81.
doi: 10.1073/pnas.1320329111. Epub 2014 Apr 21.

Radiometric 81Kr dating identifies 120,000-year-old ice at Taylor Glacier, Antarctica

Christo Buizert  1 , Daniel Baggenstos  2 , Wei Jiang  3 , Roland Purtschert  4 , Vasilii V Petrenko  5 , Zheng-Tian Lu  6 , Peter Müller  3 , Tanner Kuhl  7 , James Lee  8 , Jeffrey P Severinghaus  2 , Edward J Brook  8
Affiliations

Radiometric 81Kr dating identifies 120,000-year-old ice at Taylor Glacier, Antarctica

Christo Buizert et al. Proc Natl Acad Sci U S A. .

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.

Keywords: geochronology; glaciology; paleoclimatology.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Fig. 1.
Fig. 1.
Radiometric 81Kr dating at the Taylor Glacier BIA, Antarctica. (A) Location of Taylor Glacier on map of Antarctica with the Greenwich meridian upwards. (B) Satellite imagery of Taylor Glacier. Stratigraphically dated profiles indicated with A-A’ (along-flow), M-M’ (main transect) and D-D’ (downstream transect); length of perpendicular profiles (M and D) is not to scale. Kr-81 sampling locations are indicated as blue dots. Landsat imagery courtesy of NASA Goddard Space Flight Center and US Geological Survey. (C) Comparison of 81Kr radiometric ages to independently derived stratigraphic ages, in thousands of years before 1950 C.E. (ka B.P.).
Fig. 2.
Fig. 2.
Stratigraphic dating of Kr samples. Abbreviations are Oldest Dryas (OD), Bølling–Allerød (B-A), and Younger Dryas (YD). Measurements along the stratigraphically dated profiles (white dots) with Kr samples (black with age uncertainty). (A) Sample Kr-1, located on the main transect (Fig. 1). CH4 data from the EDML core, Antarctica (48). (B) Samples Kr-2 and 4, located on the along-flow profile. δ18Oatm data from the Siple Dome core, Antarctica (45). (C) Sample Kr-3, located on the downstream transect. δ18Oatm (δ18O of atmospheric O2) data are from EDML (46) and CH4 data are from EPICA Dome C (47). The apparent phase shift between the CH4 and δ18Oatm rise across the penultimate deglaciation is mainly a function of the large difference in the atmospheric lifetime of CH4 and O2 (45). Taylor Glacier transect positions have been corrected for the isochrone dip angle (Dataset S1). Taylor Glacier CH4 and δ18Oatm data are not shown for the along-flow and main transects, respectively, as they do not provide a strong age constraint.
Fig. 3.
Fig. 3.
Stability of atmospheric 81Kr. (A) Relative paleointensity of the geomagnetic field (56). Magnetic reversals are indicated by vertical lines. (B) Relative spallogenic production rate (orange) with relative 81Kr abundance (black). The 81Kr abundance is calculated through a convolution of the production rate with the atmospheric 81Kr residence [1/330 × exp(−t/330), with time t in ka]. (C) Estimated error in 81Kr radiometric age when assuming stable atmospheric 81Kr/Kr; positive values indicate an underestimated tKr.
See this image and copyright information in PMC

Comment in

  • Radiokrypton dating finally takes off.
    Aeschbach-Hertig W. Aeschbach-Hertig W. Proc Natl Acad Sci U S A. 2014 May 13;111(19):6856-7. doi: 10.1073/pnas.1405830111. Epub 2014 Apr 30. Proc Natl Acad Sci U S A. 2014. PMID: 24785295 Free PMC article. No abstract available.

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