Chapter 7: Trace-element variations in stalagmites: controls by climate and by karst-system processes
Ian J. Fairchild and Adam Hartland
Here we seek to address four issues. Firstly, we use strontium isotope ratios and sulphate concentrations and isotope ratios to illustrate how the changing elemental composition of the atmosphere (reflecting windiness or pollution e.g.) can be recorded in speleothems, although in the case of sulphur there can be significant lag and storage effects in the soil-ecosystem. Secondly, we illustrate how the differential dissolution rates of calcite (faster) and dolomite (slower) influences alkaline earth element chemistry in caves and speleothems, and how the occurrence of prior calcite precipitation in seasonally dry caves can be a useful signature of aridity. Thirdly, the impact of drip hydrology on speleothems is illustrated with two examples. Enrichments in alkaline earth elements tend to correspond with drier conditions. Many elements are transported preferentially in colloidal complexes, as is particularly clearly illustrated in hyperalkaline environments where the colloids are stabilized. Seasonal increases in colloidal abundance tend to be associated with enrichments in stalagmites in associated elements. Fourthly, the annual temperature cycle is difficult to recognize directly, but is seen indirectly in terms of its impact on cave air circulation, and in turn on PCO2, pH and hence sulphate concentrations in speleothems. Multiproxy approaches prove to be particularly valuable.
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