Soil Carbon Dynamics and Atmospheric Signals in Stalagmite Radiocarbon at Sofular Cave, Turkey

The climatic controls of stalagmite radiocarbon remain one focus of modern paleoclimatology due to recent efforts and achievements in radiocarbon calibration. The Hulu cave radiocarbon record (Cheng et al., 2018) has proven the potential of stalagmites from temperate climate zones for atmospheric radiocarbon reconstruction. However, a constant dead carbon fraction (DCF) in stalagmites over long periods of time is rather exceptional. In our study, a high-resolution radiocarbon record (N>100) of a U-Series dated stalagmite from Sofular Cave, Northern Turkey, with elemental Mg/Ca ratio data is presented. From 14 to 10 kyr BP, the radiocarbon signal reveals changing climatic conditions throughout Termination I with warm periods affiliated with increased soil activity and lower DCF. We observe unstable soil conditions for the period before 14 kyr BP where DCF is strongly variable between a lower threshold of ca. 5% and an upper limit of 25%. The combination of stable isotopes, element ratios, radiocarbon and U-series data allows a multi-proxy analysis of the impact of fast climate changes like D/O events on the incorporation of radiocarbon into stalagmites. Between 15 and 27 kyr BP, hydrological changes and soil carbon cycling have a large impact on limestone dissolution systematics which is reflected in fast changing DCF on sub-centennial time scales. Although the reconstruction of atmospheric radiocarbon variability is not possible for the entire growth period, the stalagmite closely reproduces the increased atmospheric radiocarbon concentration at ca. 40 kyr BP during the Laschamp geomagnetic reversal, which has been implemented into radiocarbon calibration curves with the publication of IntCal20 (Reimer et al. 2020). Our record provides new insights in the climatic influence on stalagmite radiocarbon and as to how precision and accuracy of calibration can benefit from comprehensive multi-proxy stalagmite records.

References

Cheng, H., Lawrence Edwards, R., Southon, J., et al.: Atmospheric 14C/12C changes during the last glacial period from Hulu cave, Science, 362(6420), 1293–1297, doi:10.1126/science.aau0747, 2018.

Reimer, P. J., Austin, W. E. N., Bard, E., Bayliss, A., et al.: The IntCal20 Northern Hemisphere Radiocarbon Age Calibration Curve (0–55 cal kBP), Radiocarbon, 62(4), 725-757. doi:10.1017/RDC.2020.41