The noble gas radioisotopes ⁸¹Kr (t_1/2 =229 ka), ⁸⁵Kr (t_1/2 =1 1 a) and ³⁹Ar (t_1/2 =268 a) are valuable dating tools for groundwater, ocean water and glacier ice, serving applications such as drinking water management, oc ean current tracing and climate reconstruction. Together with ¹⁴C, these radioisotopes cover an age range from present back to 1.3 million years. Due to their extremely low environmental abundances (10^-17 …10^-11 ) corresponding to only a few thousand atoms per kilogram of water or ice, their detection is very challenging and in the case of 81 Kr, has practically not been possible in the past.
In the recent two decades, the laser based method Atom Trap Trace Analysis (ATTA), which detects single atoms via their fluorescence in a magneto optical trap, has succeeded in measuring these radioisotopes on natural levels. Initially, tons of water or ice were necessary for ATTA, which severely hampered its use for dating of environmental samples. Due to progress in the ATTA instruments, the sample size could be lowered to ~10 kg of water or ice, allowing for applications such as dating of deep water from the Pacific Ocean and ice cores from Antarctica and Tibet.
In this colloquium I will present an overview of the ATTA method, recen t dating results on groundwater, ocean wate r and glacier ice as well as the latest advances towards ⁸¹Kr and ³⁹Ar dating with 1 kg of water or ice.

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I. Crotti, et al. (2021) An extension of the TALDICE ice core age scale reaching back to MIS 10.1. , Quaternary Science Reviews

J. Wang et al. (2021), Optical excitation and trapping of 81 Kr, Physical Review Letters

J. Q. Gu et al. (2022), Estimation of the Ventilation Transit Time Distribution at the Yap Mariana Junction Using ³⁹Ar, ⁸⁵Kr and ¹⁴C Tracers, JGR Oceans

D.E. Martínez , et al. ( 2022), ⁸¹Kr reveals one million year old groundwater at the Atlantic coast of Argentina as a record of Mid Pleistocene climate, Journal of Hydrology

Ritterbusch et al (2022), A Tibetan ice core covering the past 1,300 years radiometrically datedwith ³⁹Ar, Proceedings of the National Academy of Sciences