Dating of groundwater and ocean samples with noble gas radioisotopes – sample preparation and field applications

The noble gas radioisotopes 39Ar (half-life 269 yr) and 85Kr (half-life 10.8 yr) are desired tracers for dating water and ice in the past 1000 years, particularly because of their conservative properties. However, their application has long been hindered due to their low isotopic abundance and consequently, large required sample sizes. Due to recent improvements of the detection method Atom Trap Trace Analysis (ATTA), dating with 39Ar and 85Kr on a fewkilograms ofwater and ice has become feasible. In order to make this recent progress available for field studies, sample preparation systems for both argon and krypton have been set up and characterized. Argon purity and recovery > 95% could be achieved as well as a krypton purity and recovery > 90%. In the course of this thesis, these sample preparation systems could be employed in three different field studies applying 39Ar and 85Kr among other tracers. In a groundwater study, the freshwater lens on Rottnest Island inWestern Australia was investigated with a multi-tracer approach and evaluated with a lumped parameter model. Weekly atmospheric samples for 85Kr were taken in Adelaide and compared to other 85Kr monitoring stations. An interhemispheric exchange time of about seventeen months was derived from the data and 85Kr input functions for the northern and southern hemisphere could be retrieved. The third study represents the first 39Ar ocean campaign with ATTA. Twenty samples from three depth profiles near Cape Verde were taken, purified and analyzed in the context of this thesis. A fast decrease in 39Ar to under 50 pmAr below 2000m was observed and mean ages of the sampled water body were estimated by combining 39Ar with CFC-12 results. The three field applications show the importance of the noble gas radioisotopes 39Ar and 85Kr in multi-tracer studies, especially in the light of an advancing ATTA technology