20.02.2013 Views

Diploma thesis in Physics submitted by Florian Freundt born in ...

Diploma thesis in Physics submitted by Florian Freundt born in ...

Diploma thesis in Physics submitted by Florian Freundt born in ...

SHOW MORE
SHOW LESS

Create successful ePaper yourself

Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.

Chapter 2<br />

Theory<br />

2.1 Noble gas temperatures<br />

The concept of us<strong>in</strong>g dissolved noble gases <strong>in</strong> ground water as tracers for paleotemperature is<br />

based on the observed temperature dependency of gas solubility <strong>in</strong> water, the ma<strong>in</strong>ly atmospherical<br />

source of noble gases <strong>in</strong> ground water and the chemically <strong>in</strong>ert behavior of noble gases.<br />

With<strong>in</strong> the relevant temperature <strong>in</strong>terval found at ground water recharge areas the solubility<br />

decreases with <strong>in</strong>creas<strong>in</strong>g temperature, this effect is more dist<strong>in</strong>ctive for heavier noble gases.<br />

The ma<strong>in</strong> source of all stable noble gases found <strong>in</strong> meteoric and ground water is the Earth’s<br />

atmosphere. Radiogenic and terrigenic noble gas sources are of little <strong>in</strong>fluence, only 3 He, 4 He<br />

and sometimes 40 Ar are <strong>in</strong>fluenced <strong>by</strong> non-atmospheric sources [Kipfer et al., 2002]. Due to this<br />

<strong>in</strong>fluence and the small temperature dependance of its solubility, helium is not used for model<strong>in</strong>g<br />

paleotemperatures.<br />

F<strong>in</strong>ally, the chemical <strong>in</strong>ertness of the stable noble gases ensures the absence of chemical s<strong>in</strong>ks,<br />

mak<strong>in</strong>g dissolved noble gases a conservative tracer and lead<strong>in</strong>g to a preservation of the temperature<br />

<strong>in</strong>formation. This requires a conf<strong>in</strong>ed aquifer however, s<strong>in</strong>ce depressurization would cause<br />

degass<strong>in</strong>g and there<strong>by</strong> loss of the temperature <strong>in</strong>formation.<br />

When water from a conf<strong>in</strong>ed aquifer is sampled and analyzed for its noble gas concentrations,<br />

the result<strong>in</strong>g noble gas temperatures therefore represent mean annual soil temperatures at the<br />

ground water table of the recharge area. The temporal resolution of the noble gas temperatures<br />

depends on mix<strong>in</strong>g, dispersion and transport processes with<strong>in</strong> the aquifer and the accuracy of<br />

the water sample dat<strong>in</strong>g.<br />

The follow<strong>in</strong>g description of gas solubility and noble gas temperature calculation is largely based<br />

on Kipfer et al. [2002], Aeschbach-Hertig et al. [2008] and Schneider [2010].<br />

15

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!