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Title: Application of stable noble gases, 85Kr and 39Ar to investigate the freshwater lens on Rottnest Island, Western Australia
Authors: Kersting, A
Aeschbach, W
Deslandes, A
Meredith, KT
Peterson, MA
Purtschert, R
Suckow, A
Keywords: Rare gases
Tracer techniques
Fresh water
Western Australia
Saline aquifers
Ground water
Carbon 14
Climatic change
Issue Date: 13-Aug-2017
Publisher: Goldschmidt
Citation: Kersting, A., Aeschbach, W., Deslandes, A., Meredith, K., Peterson, M., Purtschert, R. & Suckow, A. (2017). Application of stable noble gases, 85Kr and 39Ar to investigate the freshwater lens on Rottnest Island, Western Australia. Presentation to Goldschmidt Paris 2017, August 13-18. Retrieved from:
Abstract: We report on a multi-tracer study of a freshwater lens on Rottnest Island west of Perth (Western Australia). The potable water supply of this carbonate island is entirely based on a shallow freshwater lens ‘floating’ on more saline water. Former studies (Bryan 2016) identified rain as the sole source of the fresh groundwater and that this very vulnerable system is threatened by anthropogenic usage and reduced rainfall due to climate change, causing salt water intrusion.Since the freshwater lens only has a thickness of approx. 20m, even the short screens of the observation wells (1-2m length) cause significant mixing of water of different ages. The combination of tritium (3H) and radiocarbon (14C) used earlier cannot resolve details of the age distribution because of the low values for tritium in precipitation on the southern hemisphere and because of mixing corrosion of the carbonate aquifer together with seawater intrusion changing the initial radiocarbon values. Therefore,this study focussed on the applicationof 85Kr(half-life 10,8yr) and 39Ar (half-life 269yr) as well as the stable noble gases. Here 85Kr complements 3H to resolve the component of very young waterin the age distribution,whereas39Ar fillsthe dating gap between 3H and 14C. The heavy noblegases (Ar, Kr, Xe) can give additional information on the infiltration of freshwater or seawater and 4He can identify admixtures of old water.
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