HOLOCENE CLIMATE AND ENVIRONMENTAL CHANGE FROM GEOCHEMISTRY OF A BELGIAN SPELEOTHEM

Speleothems are widely used as recorders of climate and environmental change. Here we report data from a speleothem collected from the Han-sur-Lesse cave in Belgium in 2000. The stalagmite has been U/Th dated, suggesting it started to grow more than 5300 years ago. Based on six U/Th dates spanning the 36 cm speleothem, an average growth rate of 7 mm per century was calculated, but growth rate increased during the last ~200 years of growth. Oxygen and carbon isotopes co-vary with speleothems from other nearby caves, but suggest a slight isotopic disequilibrium in this speleothem. Thus far only the top 16 mm have been analyzed by laser Ablation ICP-MS, with analysis of the remaining 36 cm underway. These preliminary data show a sharp steady rise in Pb over the past ~100 years, undoubtedly due to leaded gasoline. However, this steady rise is preceded by a small peak from 1894 to 1910. There is no correlation between Mg/Ca and Sr/Ca suggesting no prior calcite precipitation has affected the elemental signatures. Previous studies have shown that P, Mg and U are useful as palaeohydrological proxies and that Sr, Ba and Na are influenced by calcite precipitation rate linked to speleothem growth rate. We found some coincidence between δ¹⁸O values and Sr/Ca, Ba/Ca, and Mg/Ca, but not for P/Ca, U/Ca, or Na/Ca. Analysis of the remainder of the speleothem will allow comparison of these proxies across variable growth rates (from ~0.03 to 0.17 mm/yr).