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| Titel |
Monitoring of a fast-growing speleothem site from the Han-sur-Lesse cave, Belgium, indicates equilibrium deposition of the seasonal δ¹⁸O and δ¹³C signals in the calcite |
| VerfasserIn |
M. Van Rampelbergh, S. Verheyden, M. Allan, Y. Quinif, E. Keppens, P. Claeys |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1814-9324
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| Digitales Dokument |
URL |
| Erschienen |
In: Climate of the Past ; 10, no. 5 ; Nr. 10, no. 5 (2014-10-22), S.1871-1885 |
| Datensatznummer |
250117061
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| Publikation (Nr.) |
 copernicus.org/cp-10-1871-2014.pdf |
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| Zusammenfassung |
Speleothems provide paleoclimate information on multimillennial to decadal
scales in the Holocene. However, seasonal or even monthly resolved records
remain scarce. Such records require fast-growing stalagmites and a good
understanding of the proxy system on very short timescales. The Proserpine
stalagmite from the Han-sur-Less cave (Belgium) displays well-defined/clearly
visible darker and lighter seasonal layers of 0.5 to 2 mm
thickness per single layer, which allows a measuring resolution at a monthly
scale. Through a regular cave monitoring, we acquired a good understanding
of how δ18O and δ13C signals in modern calcite
reflect climate variations on the seasonal scale. From December to June, outside
temperatures are cold, inducing low cave air and water temperature, and
bio-productivity in the soil is limited, leading to lower pCO2 and
higher δ13C values of the CO2 in the cave air. From June
to December, the measured factors display an opposite behavior.
The absence of epikarst water recharge between May and October increases
prior calcite precipitation (PCP) in the vadose zone, causing drip water to
display increasing pH and δ13C values over the summer months.
Water recharge of the epikarst in winter diminishes the effect of PCP and as
a result the pH and δ13C of the drip water gradually decrease.
The δ18O and δ13C signals of fresh calcite
precipitated on glass slabs also vary seasonally and are both reflecting
equilibrium conditions. Lowest δ18O values occur during the
summer, when the δ13C values are high. The δ18O
values of the calcite display seasonal variations due to changes in the cave
air and water temperature. The δ13C values reflect the seasonal
variation of the δ13CDIC of the drip water, which is
affected by the intensity of PCP. This same anticorrelation of the δ18O versus the δ13C signals is seen in the monthly
resolved speleothem record that covers the period between 1976 and 1985 AD.
Dark layers display lower δ18O and higher δ13C
values. The cave system varies seasonally in response to the activity of the
vegetation cover and outside air temperature between a "summer mode" lasting
from June to December and a "winter mode" from December to June. The low
δ18O and high δ13C values of the darker speleothem
layers indicate that they are formed during summer, while light layers are
formed during winter. The darker the color of a layer, the more compact its
calcite structure is, and the more negative its δ18O signal and
the more positive its δ13C signal are. Darker layers deposited
from summer drip water affected by PCP are suggested to contain lower
Ca2+ concentration. If indeed the calcite saturation represents the
main factor driving the Proserpine growth rate, the dark layers should grow
slower than the white layers. |
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