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Read Full Article (file size: 225403 bytes) Cited by
GEOPHYSICAL RESEARCH LETTERS,
VOL. 35,
L19401,
doi:10.1029/2008GL035018,
2008
Excess air in the noble gas groundwater paleothermometer: A new model based on diffusion in the gas phase
Tie Sun
Department of Geological Sciences, University of Michigan, Ann Arbor, Michigan, USA
Chris M. Hall
Department of Geological Sciences, University of Michigan, Ann Arbor, Michigan, USA
Maria Clara Castro
Department of Geological Sciences, University of Michigan, Ann Arbor, Michigan, USA
Kyger C. Lohmann
Department of Geological Sciences, University of Michigan, Ann Arbor, Michigan, USA
Patrick Goblet
Centre de Géosciences, Ecole des Mines de Paris, Fontainebleau, France
Abstract
A key assumption for calculating paleotemperatures using noble gas concentrations in groundwater is that water equilibrates
with standard air. However, if the unsaturated zone is depleted in O2, the noble gas partial pressures will be elevated, resulting in a bias of noble gas temperatures (NGTs) to low values. This
oxygen depletion (OD) mechanism was used to explain low NGT values for a shallow aquifer in Michigan where new O2 saturation and CO2 measurements now confirm the OD model. Measured excess He, without an expected vertical concentration gradient in the water
phase, suggests that the rate of noble gas equilibration at the base of the unsaturated zone is restricted, and that transport
within the gas phase may be a rate-limiting step. A new NGT model is presented that uses the OD mechanism and that allows
for partial re-equilibration of excess air via diffusion in the gas phase.
Received 13
June
2008;
accepted 22
August
2008;
published 4
October
2008.
Keywords: noble gas;
paleoclimate;
hydrology.
Index Terms: 1620 Global Change: Climate dynamics (0429, 3309); 1829 Hydrology: Groundwater hydrology; 1833 Hydrology: Hydroclimatology; 1899 Hydrology: General or miscellaneous.
Read Full Article (file size: 225403 bytes) Cited by
Citation: Sun, T., C. M. Hall, M. C. Castro, K. C. Lohmann, and P. Goblet
(2008),
Excess air in the noble gas groundwater paleothermometer: A new model based on diffusion in the gas phase,
Geophys. Res. Lett.,
35,
L19401,
doi:10.1029/2008GL035018.
Copyright 2008 by the American Geophysical Union.
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