Climate-induced speleothem radiocarbon variability on Socotra Island from the Last Glacial Maximum to the Younger Dryas

Abstract

In this study, the dead carbon fraction (DCF) variations in stalagmite M1-5 from Socotra Island in the western Arabian Sea were investigated through a new set of highprecision U-series and radiocarbon ( 14 C) dates. The data reveal an extreme case of very high and also climate-dependent DCF. For M1-5, an average DCF of 56.2 ± 3.4 % is observed between 27 and 18 kyr BP. Such high DCF values indicate a high influence of aged soil organic matter (SOM) and nearly completely closed-system carbonate dissolution conditions. Towards the end of the last glacial period, decreasing Mg/Ca ratios suggest an increase in precipitation which caused a marked change in the soil carbon cycling as indicated by sharply decreasing DCF. This is in contrast to the relation of soil infiltration and DCF as seen in stalagmites from temperate zones.

Changes in Cave Sedimentation Mechanisms During the Late Quaternary: An Example From the Lower Cerovačka Cave, Croatia

“…The radiocarbon age was calibrated using the OxCal v 4.2.4 software (Bronk Ramsey 2009, 2016 and IntCal20 calibration curves (Reimer et al, 2020). Speleothem radiocarbon date was presented without reservoir correction (dead carbon fraction, DCF 0), with DCF of 15% which is generally used for Dinaric secondary carbonates (Horvatinčić et al, 2003), and also with DCF of 12.5% determined at the Modrič cave near the LCC location (Rudzka et al, 2012), since DCF can vary with location (Srdoč et al, 1986;Krajcar Bronić et al, 1986, 1992Sironić et al, 2020) and time (Hua et al, 2017;Bajo et al, 2017;Therre et al, 2020). Reservoir corrections were reported according to Soulet et al (2016):…”

Climatic variations during the Holocene inferred from radiocarbon and stable carbon isotopes in a high-alpine cave

“…Thus, in addition to living vegetation, which contributes atmospheric radiocarbon, an old OM source, which respires radiocarbon-depleted CO2, is required to explain depleted δ 13 C values and elevated dcf. Such old OM is also argued to have contributed to the radiocarbon reservoir effect of Moomi Cave (Socotra Island) during the last glacial period (Therre et al, 2020). Observations from other cave and karst systems also point to important C pools deep in the vadose karst, e.g., (Benavente et al, 2010;Bergel et al, 2017;Breecker et al, 2012).…”

Heidelberg Radiocarbon Lab – Establishing a New Carbon Dioxide Extraction Line for Carbonate Samples

“…A combination of high-precision and high-accuracy U-series dating from Arps (2017) and Fohlmeister et al (2018), performed on the MC-ICPMS instrument at the Institute of Environmental Physics, Heidelberg, and nine radiocarbon dating results obtained by the Heidelberg 14 C Lab Extraction Line 921 procedure described in previous sections was used. The data allowed the calculation and uncertainty modelling of the DCF according to the procedure described in Griffiths et al (2012) and Therre et al (2020) in reference to the recently published IntCal20 record (Reimer et al 2020). The DCF time-series (Figure 5) revealed extremely high values above 50%, with a high intra-record variability ranging from (49.4 ± 0.4)% to (61.6 ± 0.4)% over the last 6000 yr. Alpine speleothems have previously revealed extremely high levels of dead carbon that were attributed to the enhanced dissolution of limestone due to sulphuric acid or to aged organic matter contributions (Spötl et al 2005;Welte et al 2020), which augments the share of very old carbon in the dissolved inorganic carbon in the percolation water (Bajo et al 2017).…”

“…In several studies, 14 C measurements were used to create age models of stalagmites (Fohlmeister et al 2017;Warken et al 2018). However, in combination with the established high-accuracy and highprecision U-series dating routine (Arps 2017;Wefing et al 2017), 14 C can be used as a climate proxy to determine the influence of paleoclimate dynamics on 14 C reservoir ages of corals and stalagmites (Therre et al 2020). To measure long-term trends as well as shorttime fluctuations of radiocarbon ages with high reproducibility, a reliable and robust 14 C sample preparation and measurement routine for carbonate samples is imperative.…”

“…Our setup provides the possibility to prepare six consecutive carbonate samples (6-12 mg) in less than three hours at typical vacuum levels in the order of 10 -5 mbar. After the extraction, samples are graphitized and subsequently measured by accelerator mass spectrometry (AMS), as was previously described in Therre et al (2020). The established sample preparation procedure and the existing measurement facility provide the prerequisites for numerous future 14 C studies on paleoclimate archives.…”