Interpretation of dissolved atmospheric noble gases in natural waters

W. Aeschbach-Hertig, F. Peeters, U. Beyerle, R. Kipfer

EAWAG Ueberlandstrasse 133 Duebendorf CH-8600 Switzerland

Several studies have used the temperature dependence of gas solubilities in water to derive paleotemperatures from noble gases in groundwaters. We present a general method to infer environmental parameters from concentrations of dissolved atmospheric noble gases in water. Our approach incorporates statistical methods to quantify uncertainties of the deduced parameter values. The equilibration temperatures of water equilibrated with the atmosphere under controlled conditions could be inferred with a precision and accuracy of 0.2 C. The equilibration temperatures of lake and river samples were determined with a similar precision. Most of these samples were in agreement with atmospheric equilibrium at the water temperature. In groundwaters, either recharge temperature or altitude could be determined with high precision ( 0.3 C and 60 m, respectively), despite the presence of excess air. However, typical errors increase to 3 C and 700 m, if both temperature and altitude are determined at the same time, because the two parameters are correlated. In some groundwater samples, the composition of the excess air deviated significantly from atmospheric air, which was modeled by partial re-equilibration. In this case, the achievable precision of noble gas temperatures was significantly diminished (typical errors of 1 C).

AGU Index Terms: 3344 Paleoclimatology; 1829 Groundwater hydrology; 1845 Limnology; 3260 Inverse theory

Keywords/Free Terms: Noble gases, Groundwater, Paleotemperature, Solubility, Excess air, Inverse modeling.

Water Resour. Res., Vol. 35 , No. 9 , p. 2779

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