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.