Variability of Cosmogenic 35S in Rain-Resulting Implications for the Use of Radiosulfur as Natural Groundwater Residence Time Tracer

Michael Schubert, Kay Knöller, Ina Tegen, Lucrezia Terzi

    Research outputpeer-review


    Information about groundwater residence times is essential for sustainable groundwater management. Naturally occurring radionuclides are suitable tools for related investigations. While the applicability of several long-lived radionuclides has been demonstrated for the investigation of long residence times (i.e., years, decades, centuries and more), studies that focus on sub-yearly residence times are only scarcely discussed in the literature. This shortage is mainly due to the rather small number of radionuclides that are generally suitable for the purpose and show at the same time adequately short half-lives. A promising innovative approach in this regard applies cosmogenic
    radiosulfur (35S). 35S is continuously produced in the stratosphere from where it is conveyed to the troposphere or lower atmosphere and finally transferred with the rain to the groundwater. As soon as the meteoric water enters the subsurface, its 35S activity decreases with an 87.4 day half-life, making 35S
    a suitable time tracer for investigating sub-yearly groundwater ages. However, since precipitation shows a varying 35S activity during the year, setting up a reliable 35S input function is required for sound data evaluation. That calls for (i) an investigation of the long-term variation of the 35S activity in the rain, (ii) the identification of the associated drivers and (iii) an approach for setting up
    a 35S input function based on easily attainable proxies. The paper discusses 35S activities in the rain recorded over a 12-month period, identifies natural and anthropogenic influences, and suggests an approach for setting up a 35S input function applying 7Be as a proxy.
    Original languageEnglish
    Article number2953
    Pages (from-to)1-14
    Number of pages14
    StatePublished - 21 Oct 2020

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