Geology Reference
In-Depth Information
an adit from an abandoned Pb - Zn mine at an alti-
tude of 1090 m. The adit was opened in 1870,
partly closed in the second half of the 20th
century, and then re-opened before a door, with
slits to allow movement of bats, was installed in
1999. In this area several chambers around 200 m
into the hillside have been monitored, displaying a
remarkably congruent pattern of variation in PCO
2
through the year. Of these, S¨ulenhalle lies at a
depth of c. 70 m from the surface and is accessible
via a narrow horizontal passage opening to a
chamber several metres in size in each dimension.
The overlying vegetation is a spruce-dominated
forest underlain by a brown forest soil. Annual pre-
cipitation lies within the range 1100 - 1600 mm,
mostly in the second half of the year and the water-
excess peaks in October and November. The
temperature is below freezing normally between
November and March and the ground is snow-
covered for most of this period. The air temperature
in S¨ulenhalle, which should be close to the annual
mean, is 5.8 + 0.1 8C throughout the year and
dripwaters in the same chamber are 5.8 + 0.2 8C.
Sp¨tl et al. (2005) presented several years of
hydrochemical data from three representative drips
in the cave system which varied from near-invariant
in drip rate to displaying modest seasonal changes
through to more extreme and inter-annual variabil-
ity. Despite differences in hydrological behaviour
they showed a consistent pattern of seasonal
changes in the carbonate system, but no seasonal
variations in other chemical parameters. In the
winter: (1) pH rises, in equilibrium with changing
PCO
2
of cave air and calcite saturation rises simi-
larly; (2) d
13
C of dissolved inorganic carbon rises
from a base of 211.2 to 211.9‰ by 2 to 7‰ as iso-
topically light CO
2
is degassed; and (3) in some
drips, there is a modest decrease in Ca and alkalinity
(most precisely monitored by changes in the electro-
conductivity of the solution) indicative of some
CaCO
3
precipitation; winter precipitation is also
seen
on
the
surface
of
a
pool
(Silbersee)
in
S¨ulenhalle.
The three studied stalagmites from S¨ulenhalle
(Obi12, Obi55 and Obi84) are all approximately
cylindrical structures 3 - 4 cm in diameter fed by sta-
lactites a few cm to dm above. The elemental com-
position of four drip water sites, including the three
feeding the three stalagmites, is summarized in
Table 1. The drips feeding the studied stalagmites
are very similar in: (1) major and minor element
compositions; (2) the consistent Ca concentrations
of 51 - 53 + 5mgl
21
; and (3) calcite saturation
indices
(around
0.44 - 0.58 + 0.1)
controlled
by
seasonally changing ventilation.
Generally, no relationship between instan-
taneous measurements of drip rate and EC (electri-
cal conductivity, a proxy for total ion content) was
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