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158 CHAPTER 4. AQUATIC SYSTEMS
4.1.5 Advancing the use of noble gases as palaeoclimate indicators
Participating scientists Laszlo Palcsu, Werner Aeschbach-Hertig
Abstract A better understanding of gas partitioning during groundwater infiltration is a prerequisite
for the reliable use of noble gases as palaeoclimate proxies. The primary goal of the present project
is to obtain a detailed understanding of the physical mechanisms linking climate and soil parameters
to the noble gas patterns imprinted during groundwater recharge.
Figure 4.5: Results of stability tests of the new noble gas system, showing the deviation of different
noble gas measurements from the average (X-axis: number of measurements, Y-axis: deviation in %).
Background The analysis of dissolved noble
gas concentrations in groundwater has proven to
be a reliable method to determine quantitative
palaeotemperatures [Kipfer et al. , 2002]. Noble
gas studies in semi-arid regions have shown that
in addition to recharge temperatures, the ”excess
air” phenomenon may be useful as a proxy for
the important climate parameter humidity [Beyerle
et al. , 2003]. The present project aims at
advancing and broadening the scope and applicability
of noble gases in palaeoclimatology and hydrology,
in particular at establishing the palaeoclimatic
significance of excess air. This objective
shall be achieved by careful analysis of noble gas,
climate, and soil data from several semi-arid regions,
complemented by experiments on the scale
of laboratory soil columns and test-fields.
Methods and results To interpret the dissolved
noble gases in water as noble gas temperature
and excess air component with low error it is
necessary to achieve a very precise measurement
of noble gases. Therefore, the accuracy of each
noble gas measurement should be around 1 % or
better. Noble gas measurents are performed by a
new GV 5400 noble gas mass spectrometer which
was purchased and installed in 2004. The GV
5400 is an all-metal, statically operated, double focused,
90 ◦ sector field mass spectrometer with 57
cm extended geometry. So far, sensitivities and reproducibilities
were determined. According to the
acceptance specification, the achieved sensitivities
are 7.52·10 −4 Amps/Torr for 40 Ar, and 3.47·10 −4
Amps/Torr for 4 He, respectively. Stability and
reproducibility measurements were performed on
normal air samples. An individual sample could
be measured within a few permil relative error,
while the results of several measurements differed
from each other by 1-2 %. The standard deviation
of the 4 He and 3 He measurement were 0.6 %
and 1.2 %, whilst the measured data were varying
within the range of ±1 % and ±3 % around the
average (see Figure). The standard deviation of
the heavier noble gases were 0.3 % for neon, 0.5 %
for argon, 1.0 % for krypton, and 0.9 % for xenon.
These accuracies allow us to determine noble gas
temperatures with an error of about 0.5 ◦ C and
very precise excess air components.
Outlook/Future work Laboratory and field
experiments will be started in the next months
in order to investigate the mechanisms which are
responsible for the excess air formation. Furthermore,
using the ability for precise noble gas measurements,
the potential of fluid inclusions in stalagmites
and other carbonate deposits from caves
as palaeoclimate archives will also be investigated
(see section 4.1.4).
Funding This project is supported by the Marie
Curie Intra-European Fellowships program (reference
number: 009562).