Infiltration water organic matter and trace element geochemistry in a semi-arid karst environment: implications for speleothem paleoclimatology

A series of short-term field infiltration experiments were conducted at Wellington caves, NSW, Australia, a semi-arid karst environment. Coupled with laboratory soil leaching experiments, our results, highlight important implications for the interpretation of paleoclimate records in stalagmites in these regions. Cave dripwater was collected from two adjacent drip sites that activated during the infiltration experiment. The trace element and fluorescent dissolved organic matter (fDOM) content were analyzed. Principal component analysis showed that the variation in the dataset could be explained by two components: soil-derived and bedrock-derived. The soil component was identified based on its correlation with fDOM. Barium, magnesium, copper and nickel were also associated with the soil component. The bedrock component comprised silicon and the elements associated with carbonate such as calcium, strontium, magnesium. These results were confirmed by the soil leaching experiments. In addition to the soil leaching experiments, the site was characterized by the elemental and mineralogy analysis of soil and limestone collected from above the cave. Using the iTRAX core scanner, sediment/limestone cores collected down to 30m from the site were also analyzed and similar elemental correlations were investigated. In this semi-arid environment, barium and magnesium, elements normally bedrock associated, show different behavior. Barium is derived from the soil and magnesium is derived from both the bedrock and soil. An important observation is that magnesium, previously reported as a proxy for effective rainfall, may not be suitable tracer in semi-arid environments, due to the additional contribution from the soil. However this study has identified the potential of barium in stalagmites as a soil tracer, and silicon as a bedrock tracer, in our semi-arid environments. We present our preliminary results of LA ICPMS trace element analysis of stalagmites collected from the same site and deposited over the last 100 years. We compare the stalagmite proxy records to our laboratory and field calibration and historical climate records.