Berlin 2012 – scientific programme

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UP: Fachverband Umweltphysik

UP 9: Poster session

UP 9.14: Poster

Wednesday, March 28, 2012, 18:30–19:15, Poster F

Determination of noble gas temperatures on speleothems — •Tim Sander, Thomas Marx, Jürgen Engel, and Werner Aeschbach-Hertig — Institut für Umweltphysik, Universität Heidelberg, Germany

The solubility of noble gases in water is a function of temperature, salinity and their partial pressure in the gas phase. For known pressure and salinity, it is possible to determine the absolute temperature at the time of isolation of the water from the air by measuring the concentrations of the dissolved noble gases. These so-called noble gas temperatures (NGTs) are already widely used for determining paleotemperatures from the groundwater archive. The application of this proxy to fluid inclusions in speleothems promises the additional advantage of a better time resolution combined with precise dating.

The main problems in determining well-defined NGTs on speleothems are the presence of air and the small amount of water incorporated in the calcite. Air inclusions in speleothems carry no temperature information and mask the temperature-relevant noble gas concentrations. A stepwise extraction technique was established to separate the water from the air-filled inclusions. A reasonably small calcite sample (about 1g) includes only about one microliter of fluid inclusion water, which demands a very accurate measurement of the corresponding small noble gas amounts. In order to show that it is possible to determine well-defined temperatures on such tiny samples, the setup was tested with very small air-equilibrated water samples (µAEWs), yielding reproducibilities better than 5% for all noble gases.