Towards 81Kr and 39Ar dating with 1 kg of ice

<p>Paleoclimate reconstructions from ice core records can be hampered due to the lack of a reliable chronology, especially when the stratigraphy is disturbed and conventional dating methods cannot be readily applied. The noble-gas radioisotopes ⁸¹Kr and ³⁹Ar can in these cases provide robust constraints as they yield absolute, radiometric ages. ⁸¹Kr (half-life 229 ka) covers the time span of 30-1300 ka, which is particularly relevant for polar ice cores, whereas ³⁹Ar (half-life 268 a) with a dating range of 50-1800 a is suitable for alpine glaciers. For a long time the use of ⁸¹Kr and ³⁹Ar for dating of ice samples was impeded by the lack of a detection technique that can measure its extremely small abundance at a reasonable sample size.</p><p>We present ⁸¹Kr and ³⁹Ar dating of Antarctic and Tibetan ice cores with the detection method Atom Trap Trace Analysis (ATTA), using 5-10 kg of ice for ⁸¹Kr and 2-5 kg for ³⁹Ar. Recent studies in Antarctica include ⁸¹Kr dating in ice cores from the Larsen Blue ice area, Talos Dome and Epica Dome C. Moreover, we have used ³⁹Ar for dating an ice core from central Tibet covering the past 1500 years, in order to validate a previous timescale based on layer counting. The&#160; studies demonstrate how ⁸¹Kr and ³⁹Ar can provide age constraints and complement other methods in developing an ice core chronology. As the sample size requirement for ⁸¹Kr and ³⁹Ar analysis still hinders its use in ice cores, developments on the ATTA systems are in progress to further decrease the sample size and increase the dating precision. Here, we present our latest advances towards ⁸¹Kr and ³⁹Ar dating with ~ 1 kg of ice.</p><p>[1] Z.-T. Lu, et al. (2014) Tracer applications of noble gas radionuclides in the geosciences, <em>Earth-Science Reviews 138, 196-214</em></p><p>[2] C. Buizert et al. (2014), Radiometric ⁸¹Kr dating identifies 120,000-year-old ice at Taylor Glacier, Antarctica <em>Proceedings of the National Academy of Sciences, 111, 6876</em></p><p>[3] L. Tian et al. (2019), ⁸¹Kr Dating at the Guliya Ice Cap, Tibetan Plateau, <em>Geophysical Research Letters </em><em>46, 6636&#8211;6643</em></p><p>[4] Crotti I, et al. (2021) An extension of the TALDICE ice core age scale reaching back to MIS 10.1. Quaternary Science Reviews 266:107078</p><p>[5] Lee, G., et al. (2021) Chronostratigraphy of blue ice at the Larsen Glacier in Northern Victoria Land, East Antarctica, <em>The Cryosphere Discuss</em>. [in review]</p>