Disentangling climate-dependent stalagmite proxies using radiocarbon timeseries

The transport and incorporation mechanisms of radiocarbon (¹⁴C), stable carbon isotopes (δ¹³C) and trace metal ratios into speleothems have been investigated intensively in the past. This provides a crucial understanding for the detection of climate and ecosystem signals (precipitation, vegetation variability) or even changes in atmospheric composition like radionuclide concentration. The Dead Carbon Fraction (DCF) in tropical settings often revealed a positive correlation with hydrological proxies, highlighting its relation with the amount of soil water infiltration. In contrast, more arid regions can have dominant aged stocks of soil organic matter (SOM) diluting the ¹⁴C concentration of the soil CO₂, which is responsible for an enhanced decoupling between speleothem DCF and hydrological proxies.

Here, we present a compilation of several new and published stalagmite ¹⁴C records in context with the predominant climatic parameters controlling their carbon signature. The records cover humid, tropical climates in Puerto Rico, temperate settings in Northern Turkey, as well as semi-arid alpine caves, and arid locations on the Arabian Peninsula. The range of mean DCF values is extreme, from below 10 to more than 60 % with δ¹³C values between -10 and 0 ‰. Climate-controlled mechanisms like the sensitivity of vegetation to net-infiltration changes are revealed, especially for more arid regions where aged SOM significantly contributes to stalagmite geochemistry.

In a first application, we revisit a published multi-proxy glacial record of a stalagmite from Socotra Island, which allows us to disentangle the increasing soil infiltration towards Termination I and the resulting long-term DCF trends. This is achieved by exploiting the correlation of a humidity proxy (Mg/Ca) with DCF and implementing a transfer function to correct for soil carbon effects in ¹⁴C.

Our approach hints at vast opportunities to better understand the control mechanisms in stalagmite carbon signature and correct for climate-induced effects. Therefore, it can aid future research in the search for stalagmite records which trace, for instance, atmospheric nuclide signals or bear unresolved climate-related trends.