Regensburg 2016 – wissenschaftliches Programm

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UP: Fachverband Umweltphysik

UP 4: Poster Session

UP 4.6: Poster

Dienstag, 8. März 2016, 16:00–17:30, Foyer H41

The role of soil air composition for noble gas paleotemperature reconstruction — •Florian Jenner¹, Simon Mayer¹, Therese Weißbach¹, Werner Aeschbach¹, Bernhard Peregovich², and Carlos Machado² — ¹Institut für Umweltphysik, Heidelberg, Germany — ²UFOPA, Santarém, Brazil

Dissolved noble gases (NGs) in groundwater provide a well-established tool for paleotemperature reconstruction. However, reliable noble gas temperature (NGT) determination needs a detailed understanding of the dynamics of reactive and inert gases in the soil air with which the infiltrating water equilibrates. Due to microbial gas consumption and production, the NG partial pressures in soil air can deviate from atmospheric air, an effect that could offset NGT estimates if not taken into account. Because biological activity is expected to be particularly strong in humid tropical soils, we studied NGs in soil air as well as young groundwater at different sites near Santarém (Pará, Brazil) and for comparison near Heidelberg (Germany). Soil air data confirm a correlation between the sum value of O₂+CO₂ and NG partial pressures. We find significant NG enhancements in soil air by up to 7%. The strongest increase is observed in tropical Santarém, whereas NG excesses vary seasonally in temperate Heidelberg. An observed mass dependent fractionation of NG isotopes in Heidelberg can be explained by the seasonality of O₂+CO₂. However, there is no such effect in Santarém, indicating a year-long NG enhancement in soil air and supporting the expectation that this effect is particularly important in the tropics.