Revealing Million-year-old Water and Ice by Single Atom Counting of Noble Gas Radioisotopes

Datum 24.05.2023
Zeit16:15 Uhr
Ort ExWi B6
Referent Dr. Florian Ritterbusch (Univ. of Hefei China)
Abstract The noble gas radio isotopes 81-Kr (t 1/2 = 229 ka), 85-Kr (t 1/2 = 12 a) and 39-Ar (t 1/2 = 268 a) are valuable dating tools for groundwater, ocean water and glacier ice , serving applications such as drinking water management ocean current tracing and climate reconstruction. Together with 14-C, 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 radio isotopes 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. Here, we will present an overview of the ATTA method, recent dating results on groundwater, ocean water and glacier ice as well as our latest advances towards 81-Kr and 39-Ar dating with 1 kg of water or ice.