Petrology and geochemistry of annually laminated stalagmites from an Alpine cave (Obir, Austria): seasonal cave physiology - Tufas and Speleothems: Unravelling the Microbial and Physical Controls - page 300

An example of an incipient hiatus, representing
probably of the order of a month's gap in growth,
is shown between the 1999 and 2000 annual layers
in Figure 3a. Essentially it represents a re-nucleation
horizon where some new crystallites of diverse
optical orientation are found and which can persist
upwards (e.g. the upwards-expanding crystallite
under the word 'top' in Fig. 3a). Such an intra-year
hiatus can be seen to pass laterally into a more pro-
found pause in growth in Figure 4b and this is typi-
cally of the lamina geometry as they are traced into
the flanks of the stalagmites.
In summary, it is notable that hiatuses are devel-
oped at different times in the three specimens and
that they do not represent significant time gaps.
The presence of inter-annual slowdowns in drip
rate mentioned earlier in the paper (and found else-
where, e.g. by Baldini et al. 2006) provides a poss-
ible mechanism for hiatus development, growth
being limited by lack of ion supply through drip-
water. Where the monitored drip rates (Fig. 1) go
well below 0.36 ml hr 21 (1 ml sec 21 ), significantly
slower growth would be expected from the quanti-
tative model of Dreybrodt (1988) and Baker et al.
(1998). However, since the different drips in S¨u-
lenhalle do not vary in discharge synchronously,
this phenomenon is not of climatic significance.
At least several hundred laminae of similar type
and spacing are present at the top of the sample.
Specifically a lamina chronology for Obi84 for the
past 140 years is shown in Figure 5b. The mean
annual growth thickness is 141 + 25 mm and the
robustness of the series is shown by the low mean
relative standard deviation of measurement of any
individual year, which is 19%. Note that there is
an overall reduction in annual growth thickness
with time. This contrasts with the record in Grotta
di Ernesto stalagmites where there is a strong
increase, correlated with Northern Hemisphere
temperature trends (Frisia et al. 2003; Smith et al.
2006). An increase would also have been expected
had the opening of the mine adit at Obir had any
appreciable influence on studied cave chamber.
Hence we regard the circulation as essentially a
natural feature of the cave system, mainly utilizing
small openings in the rock.

samples is their extremely high content of Zn (typi-
cally c. 5000 ppm) and Pb (400 - 1400 ppm). These
contents tend to reduce over time, albeit somewhat
irregularly from the early 19th century to the late
20th century. Cu shows a similar trend in Obi84,
but concentrations are low. Other trace elements
(Mg, P, Mn, Y, Sr and Ba) show steady compo-
sitions, but S (present in the calcite in the form of
sulphate) increases strongly with time. This paral-
lels the impact of late 20th century pollution
recorded in speleothem ER78 from Ernesto cave
(Frisia et al. 2005). In work presented elsewhere
(Wynn et al. 2010), we confirm this using the first
in-situ micro-measurements of d 34 S in carbonate-
associated sulphate.
The trace element content explains X-ray dif-
fraction data which demonstrate that there is a small
reduction in (hexagonal) unit cell size (a ¼ 4.985 ˚ ,
c ¼ 17.042 ˚ ) compared with pure calcite (a ¼
4.9896 ˚ ,c¼ 17.06 ˚ ; Reeder 1983). The mean
composition of the top cm of the sample in molar
terms is Ca 0.989 Zn 0.0070 Mg 0.0042 Pb 0.0003 CO 3 .For
ions that form isomorphous carbonates with calcite,
there is a linear change in unit cell size with sub-
stitution of trace species and both Mg and Zn have
the effect of decreasing cell size. From data in
Reeder (1983) and Mackenzie (1983), and assuming
an additive effect of the two ions, the observed
Mg and Zn concentrations predict parameters of
a ¼ 4.986 ˚ and 17.038 ˚ , very close to the observed
values. Therefore, it is interpreted that these ions are
dominantly substituted for Ca.
For Mg and Sr, it is appropriate to calculate a
distribution coefficient to express the fractionation
in the ratio of the ion to calcium where:

(Tr=Ca) CaCO 3 ¼ K Tr (Tr=Ca) solution (1)

where Tr is the trace ion and K Tr is the distribution
coefficient, which may vary to a greater or lesser
extent with temperature, precipitation rate, crystal
morphology, or other aspects of solution chemistry
(Fairchild & Treble 2009). The resulting values in
Table 3 are reasonably consistent with those
observed by slow-growth, low ionic-strength exper-
iments and in Ernesto cave speleothems (Huang &
Fairchild 2001), but kinetic and competition
factors are known to be important for Sr (Borsato
et al. 2007).
The behaviour of sulphate is being studied in
much more detail and will be presented elsewhere,
but it should be noted that the concentrations in
drip water and in the speleothems are similar to
the Ernesto stalagmite ER78 (Frisia et al. 2005).
In both cases sulphate partitions into calcite to a
lesser extent than would be expected from the exper-
iments of Busenberg & Plummer (1985), which

Trends in chemical composition and
comparison with dripwaters
Trace elements

Figure 5 summarizes the variations in chemistry
found in stalagmites Obi84 (Fig. 5a, c) and Obi12
(Fig. 5d) over the past 200 years. Trace elements,
including some additional elements not showing
temporal variation, are also summarized in

Table 2. The most unusual feature about both