G05_P03

Towards a comprehensive understanding of the drivers of the reservoir effect (dead carbon fraction) in stalagmites - a modelling approach

Lechleitner F¹,  Day C², Welte C³, Fohlmeister J⁴, Stoll H⁵

¹Department of Chemistry, Biochemistry and Pharmaceutical Sciences and Oeschger Centre for Climate Change Research, University of Bern, Bern, Switzerland, ²Department of Earth Sciences, University of Oxford, Oxford, UK, ³Department of Earth Sciences and Laboratory of Ion Beam Physics, ETH Zürich, Zürich, Switzerland, ⁴Federal Office for Radiation Protection, Berlin, Germany, ⁵Department of Earth Sciences, ETH Zürich, Zürich, Switzerland

A growing number of stalagmite ¹⁴C records have been generated over the past decades, from multiple climatic states, ecosystem types and lithologies. A number of processes have been identified that influence speleothem ¹⁴C activities, leading to deviations from the atmospheric value (the reservoir effect). However, it has so far been difficult to extract globally relevant relationships that describe the connection between environmental conditions and stalagmite ¹⁴C values.

Using numerical forward modelling and published datasets, we present a suite of sensitivity analyses that test the relative importance of different processes and carbon pools on the stalagmite reservoir effect. To evaluate model performance, we compare the model output of key chemical parameters in dripwaters relating to stalagmite ¹⁴C (δ¹³C, pH, Ca²+) from two independent geochemical models: PHREEQC-based CaveCalc (Owen et al., 2018) and a simpler calcite dissolution model (Fohlmeister et al., 2011).

Subsequenly, we test the sensitivity of the stalagmite reservoir effect to processes that depend on climate, ecosystem and lithological parameters above the cave. In particular we focus on the impacts of: i) a large pre-aged soil OM reservoir, ii) host rock dissolution under a suite of conditions from open to closed system, iii) pyrite oxidation. These processes have been suggested to play a significant role, particularly in stalagmites that have very high reservoir effect values (> 50%). Our results help to identify whether observed variations in stalagmite reservoir effect can be realistically explained by such processes, and contribute to a global understanding of the factors influencing the stalagmite reservoir effect.