Atmospheric and Soil Signals in a Climate Dependent Stalagmite Radiocarbon Record from Northern Turkey

The climatic controls of stalagmite radiocarbon (¹⁴C) remain one focus of modern paleoclimatology due to recent efforts and achievements in ¹⁴C calibration. The Hulu cave ¹⁴C record (Cheng et al., 2018) has proven the potential of stalagmites from temperate climate zones for atmospheric ¹⁴C reconstruction. However, a constant dead carbon fraction (DCF) in stalagmites over long periods is rather exceptional. In our study, a high-resolution ¹⁴C record (N=111) of a precisely U-Series dated stalagmite from Sofular Cave (Northern Turkey) with elemental Mg/Ca ratio data is presented. A phase of low and constant DCF (12.5% ± 1.6%, N=20) between 10 and 14 kyr BP, together with relatively stable Mg/Ca ratios suggest stable hydrological soil/karst conditions above the cave. However, we observe unstable soil conditions for the period before 14 kyr BP where DCF is strongly variable between a lower threshold of approximately 5% and an upper limit of 25%. Near a phase of slow growth at ~17 kyr BP DCF as high as 38% is observed on sub-centennial timescales.  The combination of stable isotopes, element ratios, radiocarbon and U-series data allows for multi-proxy analysis of the impact of rapid climate changes like D/O events on the incorporation of ¹⁴C into stalagmites. Between 15 and 27 kyr BP, hydrological changes have a large impact on limestone dissolution systematics which is reflected in fast DCF variations on sub-centennial timescales. A growth stop between 21 and 23 kyr BP is resolved. Although a comprehensive reconstruction of atmospheric ¹⁴C variations is not possible for the entire growth period, the stalagmite reproduces the deviation from the IntCal13 record (Reimer et al. 2013) seen in the Hulu ¹⁴C data at ~40 kyr BP during the Laschamp geomagnetic reversal and provides further inside on the climate dependency of ¹⁴C incorporation in stalagmites.

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., Bard, E., Bayliss, A., et al.: IntCal13 and Marine13 Radiocarbon Age Calibration Curves 0–50,000 Years cal BP, Radiocarbon, 55(4), 1869–1887, doi:10.2458/azu_js_rc.55.16947, 2013.