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Should we correct speleothem carbon isotope records for degassing and prior calcite precipitation?

The carbon isotopic signature acquired from soil/epikarst processes may be a primary environmental signal of interest to interpret from speleothem d13C. However, this signal can be modified by prior calcite precipitation effects. To date, despite laboratory demonstration of PCP effects and increasingly sophisticated models fo the governing processes, there has been limited effort to deconvolve the dual PCP and soil/epikarst effects on measured speleothem carbon isotope time series. In this contribution we evaluate the feasibility, advantages, and disadvantages of using trace element ratios and the d44Ca calcium isotopic ratio to estimate PCP and isolate its contribution to the measured speleothem d13C. We assess the challenges in the PCP indicators, such as incongruent dissolution, detrital influence on trace elements, and temperature or saturation effects on partitioning. We use the CaveCalc model of multi-step degassing with equilibrium fractionation to estimate the minimum contribution of PCP on the measured d13C. We compare the resulting estimated initial (without PCP) d13C calculated for the speleothem with cave monitoring data of d13C of undegassed DIC in the modern system. We contrast the potential for estimates of absolute initial d13C with the potential to estimate the temporal trends in initial d13C.


Heather Stoll1, Franziska Lechleitner2, Christopher Day3, Oliver Kost1, Laura Endres1, Carlos Perez4
1ETH Zurich, Switzerland; 2University Bern, Switzerland; 3Oxford University, UK; 4Xian University, China
GeoKarlsruhe 2021