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We present the first successful 81Kr-Kr radiometric dating of ancient polarice. Krypton was extracted from the air bubbles in four ~350 kg polar icesamples from Taylor Glacier in the McMurdo Dry Valleys, Antarctica, and datedusing Atom Trap Trace Analysis (ATTA). The 81Kr radiometric ages agree withindependent age estimates obtained from stratigraphic dating techniques with amean absolute age offset of 6 +/- 2.5 ka. Our experimental methods and samplingstrategy are validated by 1) 85Kr and 39Ar analyses that show the samples to befree of modern air contamination, and 2) air content measurements that show theice did not experience gas loss. We estimate the error in the 81Kr ages due topast geomagnetic variability to be below 3 ka. We show that ice from theprevious interglacial period (MIS 5e, 130-115 ka before present) can be foundin abundance near the surface of Taylor Glacier. Our study paves the way forreliable radiometric dating of ancient ice in blue ice areas and margin siteswhere large samples are available, greatly enhancing their scientific value asarchives of old ice and meteorites. At present, ATTA 81Kr analysis requires a40-80 kg ice sample; as sample requirements continue to decrease 81Kr dating ofice cores is a future possibility.

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