Systematic improvement of 39Ar Atom Trap Trace Analysis and its application to derive a millennial palaeotemperature record from groundwater

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The noble gas radioisotope 39Ar is unique, as it is the sole isotope to cover the important age range of about 50 to 1000 yr. Hence it is of great interest for dating in oceanography, glaciology, and hydrogeology. The development of Atom Trap Trace Analysis (ATTA) has rendered 81Kr dating possible and has the potential to open up fundamentally new applications of 39Ar. In a previous project we have for the first time demonstrated that 39Ar analysis of natural samples by ATTA is possible. Building on the experience gathered in that previous project and additional preliminary work, the present project shall create the intellectual and instrumental foundations of ATTA for 39Ar (ArTTA) as a new tool in isotope hydrology. We aim at advancing ArTTA from the proof-of-principle stage to a fully established method and to conduct its first comprehensive application. Based on the available expertise in groundwater and palaeoclimate research and using the advantages of groundwater as a testbed for ArTTA, we plan to derive the first detailed palaeotemperature record for the past millennium from groundwater. We have identified the following two central objectives: 1. Significant improvement of the efficiency of the ArTTA device. Enhancing the count rate is necessary to improve the sample throughput as well as the achievable measurement precision. 2. Realization of the first complete study of 39Ar-dating of groundwater by ArTTA, in order to assess groundwater age distributions and palaeoclimate evolution on the timescale of centuries.