HETEROGENEITY IN TRACE ELEMENT INCORPORATION AND THE DEVELOPMENT OF µ-XRF SPECTROMETRY CALIBRATION FOR LOW-SR SPELEOTHEMS

Geochemical proxies from speleothem calcite have been shown to be important indicators of past climate variability. Trace metal Sr concentration has been utilized in paleoclimate reconstructions as an indicator of the residence time of water in the epikarst, which is a direct result of the amount of effective precipitation and infiltration into the karst system. During periods of low precipitation, higher concentrations of Sr speleothem calcite can result through an increase in water residence time as well as through the process of prior calcite precipitation, which serves to decrease Ca relative to Sr.

The utilization of conventional down-axis transects in geochemical analysis of speleothems prompts the investigation of proxy behavior along flank-thinning laminae. Sr excursions evidenced through abrupt variations in Sr concentration should be investigated as a consequence of changes in the meteoric precipitation regime or the heterogeneous incorporation of Sr. Using the Bruker Artax µ-XRF spectrometer, area scans of multiple speleothems reveal varying degrees of heterogeneity in Sr counts along laminae. The use of area scans in trace metal acquisition in speleothems can aid in understanding the timing and duration of climatic changes.

Many speleothem samples, particularly those that are fast-growing, are not typically good candidates for the use of µ-XRF in Sr analysis. Low Sr values necessitate much longer count times for each measurement, which can prohibit the construction of high-resolution records. Here we present methods and a low-Sr counts-to-concentration calibration in speleothems, with direct implications for those speleothems from tropical regions.