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UP: Fachverband Umweltphysik

UP 13: Postersession Bodenkunde, Kryosphäre, Meßtechnik, Ozeanographie

UP 13.25: Poster

Donnerstag, 26. März 2015, 10:45–19:45, G/Foyer

Dynamics of reactive and inert gases in soil air and groundwater in the context of noble gases as environmental tracers — •Simon Mayer, Florian Jenner, and Werner Aeschbach-Hertig — Institut für Umweltphysik, Heidelberg, Deutschland

A detailed understanding of the dynamics of reactive and inert gases in the subsurface is important for reliable gas tracer studies such as noble gas (NG) temperature determination and groundwater dating. Our study provides a long-term record of NG, SF₆ and CFCs in both soil air and groundwater at different sites near Heidelberg (Germany) as well as a NG analysis in a tropical region (Santarém, Brazil). The influence of soil respiration is investigated by O₂, CO₂, soil temperature and moisture measurements.

Measured NG partial pressures in soil air show an increase with respect to atmospheric air by up to 12%. In Heidelberg, this enhancement occurs as a seasonal effect. Here, a mass-dependent fractionation is caused by varying diffusivities of different isotopes. In Santarém, such fractionation effects were not observed, indicating a NG enhancement with respect to the atmosphere during the entire year.

SF₆ concentrations in soil air correspond to the mean local atmospheric mixing ratio which is enhanced in the study area near Heidelberg due to industrial sources by more than 12% with respect to the mean concentration in the Northern hemisphere. Thus a reliable correction of the local atmospheric input curve is possible for groundwater dating.