Drivers of speleothem carbon isotope and radiocarbon variability explored using Earth System Model output as input of a dripwater and speleothem chemistry model
- 1Institute for Environmental Physics, Ruprecht-Karls-Universität Heidelberg, Im Neuenheimer Feld 229, 69120 Heidelberg, Germany
- 2Helmholtz Centre for Environmental Research – UFZ, Permoserstr. 15, 04318 Leipzig, Germany
- 3Max Planck Institute for Meteorology, Bundesstr. 53, 20146 Hamburg, Germany
- 4Institute of Earth Sciences, Ruprecht-Karls-Universität Heidelberg, Im Neuenheimer Feld 236, 69120 Heidelberg, Germany
Interpreting carbon isotopes in speleothems is challenging due to the multiple interacting in-soil and in-cave chemical processes. The degree of free soil CO2, the relative abundance of aged soil organic matter (SOM) and bedrock dead carbon modifies the carbon isotopic composition in speleothems in addition to fractionation during speleothem formation or prior calcite precipitation. Knowledge of the relevant drivers of DCF and stable C isotope variability may help deciphering the climate impact imprinted on speleothem carbon isotopes.
Here, we combine Earth System Model output (Max Planck Institute Earth System Model version 1.2, Kleinen et al. 2020), a simplistic soil model, IntCal20, and the speleothem chemistry and isotope equilibrium model CaveCalc (Owen et al., 2018) to produce 25'000 yearlong DCF and d13C time series for numerous speleothems and several cave environments.
The modelling results are tuned to reasonable agreement with the respective DCF and d13C mean measurement values at each cave location for intermediate openness values of 5-120 L/kg. However, all model tuning attempts fail to reproduce fast (centennial) isotope and DCF variability. To overcome this limitation, we explore possibilities to include climate driven changes in vegetation, aged SOM, and how water availability drives the openness of the dissolution system. Extending the modelling framework to include vegetation changes produces d13C time series with more small-scale variability. Interestingly, accounting for aged SOM not only results in higher modelled DCF values, but also adds small-scale variability, assuming 20% higher fractions of aged SOM with mean soil ages for each cave location from Shi et al. (2020). Thus, our modelling efforts permit exploring the role of climate and Karst chemical processes to investigate DCF and d13C variability in speleothems over millennial time scales.
References:
Kleinen, T., Mikolajewicz, U., and Brovkin, V.: Terrestrial methane emissions from the Last Glacial Maximum to the preindustrial period, Clim. Past, 16, 575–595, doi:10.5194/cp-16-575-2020, 2020.
Owen, R., Day, C. C., and Henderson, G. M.: CaveCalc: A new model for speleothem chemistry & isotopes, Computers & Geosciences, 119, 115–122, doi:10.1016/j.cageo.2018.06.011, 2018.
Shi, Z., Allison, S.D., He, Y. et al.: The age distribution of global soil carbon inferred from radiocarbon measurements, Nature Geoscience, 13, 555–559, doi:10.1038/s41561-020-0596-z, 2020.
How to cite: Seubert, P., Frank, N., Hubig, A., Kleinen, T., and Warken, S.: Drivers of speleothem carbon isotope and radiocarbon variability explored using Earth System Model output as input of a dripwater and speleothem chemistry model , EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-13027, https://doi.org/10.5194/egusphere-egu23-13027, 2023.
