Title: Seasonal microclimate control of calcite fabrics, stable isotopes and trace elements in modern speleothem from St Michaels Cave, Gibraltar
Abstract: Abstract Detailed monitoring of three drip sites in New St Michael's Cave, Gibraltar, reveals a strongly coherent seasonal pattern of dripwater chemistry despite each site having significantly different flow paths and discharge patterns. Calcite saturation is closely linked to regular seasonal variations in cave air pCO 2 caused by seasonally reversing ventilation driven by temperature difference between the cave interior and the air outside. A coupled model of CO 2 degassing and calcite precipitation links seasonal δ 13 C variations in coexisting dripwater, cave air CO 2 and speleothem calcite to large variations in pCO 2 that are driven by cave ventilation. The relationships between stable isotope ratios, Sr/Ca and speleothem fabrics across annually formed calcite laminae are consistent with a degassing–calcite precipitation process in which rapid degassing controls the δ 13 C of both drip water DIC and calcite whereas a much slower rate of calcite precipitation causes seasonal cycles of Sr in a more complex manner. By demonstrating the causes of laminated speleothem fabrics plus trace element and isotope cycles in modern speleothem from a closely monitored cave, this study provides clear links between the local microclimate and the proxy record provided by speleothem geochemistry. In Gibraltar, low cave air pCO 2 in summer is unusual compared to what has been revealed by cave monitoring carried out elsewhere and shows that caution is needed when linking paired speleothem fabrics to specific seasons without knowledge of local processes operating in the cave.
Publication Year: 2010
Publication Date: 2010-01-01
Language: en
Type: article
Indexed In: ['crossref']
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Cited By Count: 112
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