Noble gas data from the Great Artesian Basin provide a temperature record of Australia on time scales of 105 years

 

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

Department of Environmental Physics, Swiss Federal Institute of Technology (ETH) Zurich and Swiss Federal Institute of Environmental Science and Technology (EAWAG), CH-8600 Dübendorf, Switzerland

 

Abstract

We report noble gas data from 13 artesian wells in the south-western part of the Great Artesian Basin (GAB) in Australia. Atmospheric noble gases dissolved in groundwater allow to reconstruct past soil temperatures of the recharge area and radiogenic noble gas abundances yield estimates of the groundwater residence time. All measured samples have large excesses of He relative to atmospheric solubility equilibrium. The 4He excess that generally tends to increase in direction of a supposed groundwater flow towards the central part of the investigated area is correlated with an increasing 40Ar/36Ar ratio. The calculated radiogenic 40Ar/4He ratio is 0.019±0.004, which is an order of magnitude lower than the radiogenic 40Ar/4He production ratio in crustal rocks. Radiogenic 4He concentrations, which were calibrated against 81Kr groundwater ages, yield groundwater residence times up to 550 kyr. The noble gas temperatures calculated from the atmospheric noble gas concentrations show clear fluctuations of the soil temperature in Australia during the last 550 kyr. These results suggest that the noble gas temperature method can be applied to reconstruct continental paleoclimate conditions on time scales up to a few hundred kyr.

 


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