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

Abstract

We present the first successful 81Kr-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 81Kr 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 1) 85Kr and 39Ar analyses that show the samples to be free of modern air contamination, and 2) air content measurements that show the ice did not experience gas loss. We estimate the error in the 81Kr ages due to past geomagnetic variability to be below 3 ka. We show that ice from the previous interglacial period (MIS 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 81Kr analysis requires a 40-80 kg ice sample; as sample requirements continue to decrease 81Kr dating of ice cores is a future possibility.

References in corpus (4)

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• Ar-39 Detection at the 10^-16 Isotopic Abundance Level with Atom Trap Trace Analysis
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Cited by in corpus (5)

• ${}^{81}$Kr dating at the Guliya ice cap, Tibetan Plateau
• Dating glacier ice of the last millennium by quantum technology
• First experimental determination of the ${}^{40}$Ar($n,2n$)${}^{39}$Ar reaction cross section and ${}^{39}$Ar production in Earth's atmosphere
• A VUV light source for enhanced production of metastable krypton and xenon beams
• Tracer Applications of Noble Gas Radionuclides in the Geosciences