Towards 81Kr and 39Ar dating with 1 kg of ice
Authors: Ritterbusch Florian , Crotti Ilaria , Dong Xi-Ze , Fourré Elise , Gu Ji-Qiang , Jacob Roxanne , Jiang Wei , Landais Amaëlle , Lu Zheng-Tian , Orsi Anaïs , Prié Frédéric , Shao Lili , Tian Lide , Tong A-Min , Yang Guo-Min , Wang Jie 
Published: March 2022

&lt;p&gt;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 &lt;sup&gt;81&lt;/sup&gt;Kr and &lt;sup&gt;39&lt;/sup&gt;Ar can in these cases provide robust constraints as they yield absolute, radiometric ages. &lt;sup&gt;81&lt;/sup&gt;Kr (half-life 229 ka) covers the time span of 30-1300 ka, which is particularly relevant for polar ice cores, whereas &lt;sup&gt;39&lt;/sup&gt;Ar (half-life 268 a) with a dating range of 50-1800 a is suitable for alpine glaciers. For a long time the use of &lt;sup&gt;81&lt;/sup&gt;Kr and &lt;sup&gt;39&lt;/sup&gt;Ar 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.&lt;/p&gt;&lt;p&gt;We present &lt;sup&gt;81&lt;/sup&gt;Kr and &lt;sup&gt;39&lt;/sup&gt;Ar dating of Antarctic and Tibetan ice cores with the detection method Atom Trap Trace Analysis (ATTA), using 5-10 kg of ice for &lt;sup&gt;81&lt;/sup&gt;Kr and 2-5 kg for &lt;sup&gt;39&lt;/sup&gt;Ar. Recent studies in Antarctica include &lt;sup&gt;81&lt;/sup&gt;Kr dating in ice cores from the Larsen Blue ice area, Talos Dome and Epica Dome C. Moreover, we have used &lt;sup&gt;39&lt;/sup&gt;Ar 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&amp;#160; studies demonstrate how &lt;sup&gt;81&lt;/sup&gt;Kr and &lt;sup&gt;39&lt;/sup&gt;Ar can provide age constraints and complement other methods in developing an ice core chronology. As the sample size requirement for &lt;sup&gt;81&lt;/sup&gt;Kr and &lt;sup&gt;39&lt;/sup&gt;Ar 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 &lt;sup&gt;81&lt;/sup&gt;Kr and &lt;sup&gt;39&lt;/sup&gt;Ar dating with ~ 1 kg of ice.&lt;/p&gt;&lt;p&gt;[1] Z.-T. Lu, et al. (2014) Tracer applications of noble gas radionuclides in the geosciences, &lt;em&gt;Earth-Science Reviews 138, 196-214&lt;/em&gt;&lt;/p&gt;&lt;p&gt;[2] C. Buizert et al. (2014), Radiometric &lt;sup&gt;81&lt;/sup&gt;Kr dating identifies 120,000-year-old ice at Taylor Glacier, Antarctica &lt;em&gt;Proceedings of the National Academy of Sciences, 111, 6876&lt;/em&gt;&lt;/p&gt;&lt;p&gt;[3] L. Tian et al. (2019), &lt;sup&gt;81&lt;/sup&gt;Kr Dating at the Guliya Ice Cap, Tibetan Plateau, &lt;em&gt;Geophysical Research Letters &lt;/em&gt;&lt;em&gt;46, 6636&amp;#8211;6643&lt;/em&gt;&lt;/p&gt;&lt;p&gt;[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&lt;/p&gt;&lt;p&gt;[5] Lee, G., et al. (2021) Chronostratigraphy of blue ice at the Larsen Glacier in Northern Victoria Land, East Antarctica, &lt;em&gt;The Cryosphere Discuss&lt;/em&gt;. [in review]&lt;/p&gt;