Ams Radiocarbon Dating Problems between 10 and 8 Ka Bp in Lacustrine Deposits from Lake Gun Nur, Northern Mongolia

Accelerator mass spectrometry (AMS) radiocarbon dating a continuous core from Lake Gun Nur, northern Mongolia, shows a period between 10 and 8 ka BP that could not be dated accurately. Further dating on alkali-insoluble residue and humic acid from the same samples in the Gun Nur core suggest that this AMS 14C date anomaly is neither analytical nor material related. We hypothesize that the 14C anomaly may be derived from increasing production rates of 14C caused by diminished solar activity, a low CO2/CO ratio in the atmosphere, or an unstable 14C flux in the lower atmosphere caused by changing geomagnetic field strength. Our results imply that the 14C data used for 14C age calibration cannot correct the agedepth regression between 8 and 10 ka BP to fit the age-depth model along with other time intervals.