Geology Reference
In-Depth Information
Table 4. Indicative ICP-MS analyses (in ppb) of drip water trace element compositions for SH3 (Obi55,
month-long collection) and SH4 (Obi84, instantaneous collection)
Al
Si
P
Fe
Cu
Zn
Sr
Y
Ba
Pb
SH3 (n ¼ 12)
mean
31
781
48
287
6.7
48
38
0.020
128
3.0
stdev
31
295
76
36
5.5
24
2
0.023
4
2.3
SH4 (n ¼ 6)
mean
33
707
38
270
4.8
48
34
0.021
115
2.9
stdev
29
240
14
38
0.8
25
2
0.021
8
2.1
Table 5. Summary of water-calcite partitioning calculations for the top 10 mm of Obi84 (SH4) from data in
Tables 1 and 4
Ca
Mg
Cu
Zn
Y
Pb
Distribution coefficient, calculated
-
0.017
0.059
9.1
0.122
22
% efficiency of removal
0.63
0.010
0.04
5.7
0.076
14
variability has been demonstrated (e.g. Johnson
et al. 2006; Mattey et al. 2008).
next year's growth. A similar approach was taken
to analyzing the last few years of growth at the top
of the sample (Fig. 7). Here laminae were not
visible in the precise area analyzed, but their
thicknesses on a lateral part of the section are in
agreement with the lamina positions that can be
deduced from the P peaks (although it should
be noted that the 1997 P peak is very small and
the 2000 P peak is double). Again the low-S
analyses are found to be overlapping with and fol-
lowing the P peaks, consistent with their formation
during the winter period. An additional feature of
Figure 7 is that an overall decline in mean S/Cis
found which is consistent with the fall in aqueous
sulphate observed from dripwater monitoring data
from 2002 - 2004 (Sp¨tl et al. 2005) as the catch-
ment recovers from the effects of acid deposition
in the late 20th century.
Sulphate
Sulphate can be expected to vary in abundance with
seasonal ventilation because of the influence of pH
on its incorporation into calcite. Frisia et al.
(2005) noted a significant annual variation in sul-
phate in stalagmite ER78 from Ernesto Cave
which was attributed to pH changes, based on the
model of Busenberg & Plummer (1985). These
authors proposed that sulphate incorporation could
be modelled by a distribution coefficient approach
where the ratio of interest [cf. equation (1)] was
SO 22 /CO 22 . Since aqueous sulphate does not
vary through the year, and the abundance of CO 22
is primarily controlled by pH in terms of its over-
riding control on the ratio of HCO 3 2 (the more abun-
dant species) to CO 22 , a low value for sulphate in
the speleothem each winter would be expected.
As was done by Frisia et al. (2005), synchrotron
radiation was used to confirm that S in Obi84 was
present as sulphate using the position of the domi-
nant X-ray absorption peak. However, quantitative
analysis of S content was impossible by this method
because the Ka emission line was swamped by Pb.
Instead, the ion microprobe was used to analyze S,
utilizing negative secondary ions, which permitted
the simultaneous determination of P. Results for
the 1958 - 1966 laminae illustrate that P peaks lie
close to or precisely on the visible event lamina.
In comparison with this, S also shows annual-scale
variability, but it is offset from P. Figure 6a illus-
trates that in most cases the low values also occur
predominantly from around the time of deposition
of the visible lamina through to the first half of the
Event laminae
Smith et al. (2009) reported ion probe analyses of
positive secondary ions from the Obir stalagmites
which demonstrated a strong annual covariation of
H, P, Na and Mg with enrichments centred around
the event laminae, where Sr decreases. The Sr
pattern was found to be most reliable for using
trace element layers to determine the rate of stalag-
mite growth. For Obi84, a principal component
analysis found that this explained 55% of the vari-
ation in elemental chemistry, with a further 23%
being explained by an independent mode of Sr and
Ba variability (these results were obtained on data
from which long-term trends had been removed).
This pattern of variability is illustrated for the
years 1958 - 1966 in Figure 8a. A discrepancy with
Grotta di Ernesto stalagmites is that Mg increases
 
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