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2002; Frisia et al. 2003; Mattey et al. 2008), and
recent studies also suggest that the seasonality of
calcite deposition can affect stalagmite stable
isotope signatures (Baldini et al. 2005; Treble
et al. 2005; Baldini et al. 2008). Because stalagmite
growth rates affect how other paleoclimate proxy
records are recorded, fully understanding how
cave atmosphere P
CO
2
fluctuates and what effects
these shifts may have on stalagmite formation
is critical.
Previous researchers (Dreybrodt 1980;
Buhmann & Dreybrodt 1985a, b; Dreybrodt 1996)
used rate equations derived from the Plummer-
Wigley-Parkhurst (PWP) equation (Plummer et al.
1978; Busenberg&Plummer 1987) to predict calcite
deposition on stalagmites. Theoretical calcite
accumulation rates on stalagmites can therefore be
predicted based on multiple growth determining
variables such as thin film thicknesses, drip rate,
temperature, drip water [Ca
2þ
], and cave atmos-
phere P
CO
2
. However, studies attempting to use sta-
lagmites with well-constrained growth rates to
verify these theoretical results were only moderately
successful (Baker et al. 1998). One of the more
poorly characterized growth determining variables
at the studied cave sites was cave air P
CO
2
, and
better quantification through high resolution seaso-
nal studies might yield higher correlations.
Recent studies suggest that stalagmite growth
rates can be modelled more accurately if annual
ventilation and cave atmosphere P
CO
2
variations,
along with hydrochemical parameters, are known
(Baldini et al. 2008; Mattey et al. 2008). In this
study, our current understanding of the origins, dis-
tribution, and temporal variability of cave air P
CO
2
is
discussed, and the mechanisms through which cave
air P
CO
2
affects stalagmite climate records are
identified.
comparison of the spatial P
CO
2
variability in two
Belgian caves where respired CO
2
was absorbed
by a breathing apparatus filled with sodium carbon-
ate. A linear relationship existed between the dis-
tance from the cave entrances and cave air P
CO
2
.
Based on the CO
2
distribution in the caves, the
soil zone and an underground stream flowing
through one of the caves were inferred as two CO
2
sources. Another study presented data from
Belgium and numerous other countries, and demon-
strated that P
CO
2
is positively correlated with above-
ground temperature (Ek & Gewelt 1985) and that
P
CO
2
concentrations are higher near the ceiling of
passages. A study of the Aven d'Orgnac in France
suggested that air enriched with biogenic CO
2
moved through bedrock fissures into the cave
(Bourges et al. 2001). Troester & White (1984)
demonstrated that groundwater, in this case a cave
stream, can act as either a source or a sink for
CO
2
. Several studies have monitored cave air CO
2
in tourist caves in order to mitigate damage to
either speleothems or to pictographs (Pulido-Bosch
et al. 1997; Faimon et al. 2004; Denis et al. 2005),
and have shown that human respiration is a signifi-
cant source of CO
2
in these situations. Ahigh-spatial
resolution P
CO
2
surveywas conducted for a small cave
site in southern Ireland and demonstrated that cave air
P
CO
2
increased not with depth below the ground, but
with distance from the entrance (Fig. 2) (Baldini
et al. 2006). It also suggested that CO
2
at the site
was principally derived from soil organic matter
decay and root respiration. A five-month time-series
P
CO
2
dataset from the same site confirmed this
source, but also demonstrated that ventilation
played a key role in modulating the amount of CO
2
stored in the subsurface (Baldini et al. 2008). The
importance of ventilation was also well illustrated in
studies in Austria (Sp¨tl et al. 2005), Texas (Banner
et al. 2007) and Gibraltar (Mattey et al. 2008).
Cave air P
CO
2
can be measured by using meters
containing a chemical (usually hydrazine hydro-
chloride) whose colour changes depending on the
P
CO
2
, or by using more precise electronic meters
that use the absorptivity of infrared radiation by
CO
2
to calculate the P
CO
2
. Most modern studies
typically utilise the IR technology because it
allows the logging of P
CO
2
over long periods of
time rather than just obtaining a brief snapshot.
They also permit automatic logging without the
presence of an operator whose respiration might
otherwise affect the accuracy of the measurement.
Previous research and technology
Many previous researchers have measured P
CO
2
in caves but, until recently, very little research
existed combining high resolution spatial and/or
temporal P
CO
2
measurements. One difficulty was
that the presence of an operator alters the P
CO
2
values of the measurement. The P
CO
2
of human
respiration is approximately 4% atm, much higher
than the ambient P
CO
2
of most cave sites. Studies
illustrate that after five minutes a human presence
in a cave raises the P
CO
2
by c. 30% (assuming
an original P
CO
2
of 0.4% atm) (Ek & Gewelt
1985). If accurate measurements are important,
it is therefore imperative to use a breathing
apparatus to minimise the effects of respired P
CO
2
,
or to log P
CO
2
automatically without a human oper-
ator present. Gewelt & Ek (1983) published a
Cave air sources and circulation
Identifying CO
2
sources and sinks, and characteriz-
ing the dynamics of CO
2
in cave air, are critical for
modelling how cave air P
CO
2
might have varied in
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