Preprints
https://doi.org/10.5194/cp-2022-77
https://doi.org/10.5194/cp-2022-77
 
10 Oct 2022
10 Oct 2022
Status: this preprint is currently under review for the journal CP.

Distinguishing the vegetation and soil component of δ13C variation in speleothem records from degassing and prior calcite precipitation effects

Heather M. Stoll1, Chris Day2, Franziska Lechleitner3, Oliver Kost1, Laura Endres1, Jakub Sliwinski1, Carlos Pérez-Mejías4, Hai Cheng4, and Denis Scholz5 Heather M. Stoll et al.
  • 1Department of Earth Sciences, ETH Zurich, Sonneggstrasse 5, 8006 Zürich, Switzerland
  • 2Department of Earth Sciences, University of Oxford, South Parks Road, OX1 3AN Oxford, UK
  • 3Department of Chemistry and Biochemistry & Oeschger Centre for Climate Change Research, University of Bern, Freiestrasse 3, 3012 Bern, Switzerland
  • 4Institute of Global Environmental Change, Xi’an Jiaotong University, Xi’an, China
  • 5Institute of Geosciences, University of Mainz, Mainz, Germany

Abstract. The carbon isotopic signature inherited from soil/epikarst processes may be modified by degassing and prior calcite precipitation (PCP) before its imprint on speleothem calcite. Despite laboratory demonstration of PCP effects on carbon isotopes and increasingly sophisticated models of the governing processes, to date, there has been limited effort to deconvolve the dual PCP and soil/epikarst components in measured speleothem isotopic time series. In this contribution, we explore the feasibility, advantages, and disadvantages of using trace element ratios and δ44Ca to remove the overprinting effect of PCP on measured δ13C to infer the temporal variations in the initial δ13C of dripwater. In 8 examined stalagmites, the most widely utilized PCP indicators Mg/Ca and δ44Ca covary as expected. However, Sr/Ca does not show consistent relationships with δ44Ca so PCP is not universally the dominant control on Sr/Ca. From δ44Ca and Mg/Ca, our calculation of PCP as fCa, fraction of initial Ca remaining at the deposition of the stalagmite layer, yields multiple viable solutions depending on the assumed δ44Ca fractionation factor and inferred variation in DMg. Uncertainty in the effective fractionation of δ13C during degassing and precipitation contributes to uncertainty in the absolute value of estimated initial δ13C. Nonetheless, the trends in initial δ13C are less sensitive to these uncertainties. In coeval stalagmites from the same cave spanning 94 to 82 ka interval, trends in calculated initial δ13C are more similar than those in measured δ13C, and reveal a common positive anomaly initial δ13C during a stadial cooling event. During deglaciations, the trend of greater respiration rates and higher soil CO2 is captured in the calculated initial δ13C, despite the tendency of higher interglacial dripwater situation to favor more extensive PCP.

Heather M. Stoll et al.

Status: open (until 08 Jan 2023)

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Heather M. Stoll et al.

Heather M. Stoll et al.

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Short summary
Stalagmites formed in caves provide valuable information about past changes in climate and vegetation conditions. In this contribution, we present a new method to better estimate past changes in the soil and vegetation productivity using the carbon isotopes and trace elements measured in stalagmites. Applying this method to other stalagmites should provide a better indication of past vegetation feedbacks to climate change.