Calibration is a fundamental stage of the radiocarbon (14C) dating process if one is to derive meaningful calendar ages from samples' 14C measurements. For the first time, the IntCal09 calibration curve (Reimer et al. 2009) provided an internationally ratified calibration data set across almost the complete range (0 to 50,000 cal BP) of the 14C timescale. However, only the last 12,550 cal yr of this record are composed of terrestrial data, leaving approximately three quarters of the 14C timescale necessarily calibrated via less secure, marine records (incorporating assumptions pertaining to the temporally variable “marine reservoir effect”). The predominantly annually laminated (varved) sediment profile of Lake Suigetsu, central Japan, offers an ideal opportunity to derive an extended terrestrial record of atmospheric 14C across the entire range of the method, through pairing of 14C measurements of terrestrial plant macrofossil samples (extracted from the sediment) with the independent chronology provided through counting of its annual laminations.
This paper presents new data (182 14C determinations) from the upper (largely non-varved) 15 m of the Lake Suigetsu (SG06) sediment strata. These measurements provide evidence of excellent coherence between the Suigetsu 14C data and the IntCal09 calibration curve across the last ~12,000 cal yr (i.e. the portion of IntCal based entirely on terrestrial data). Such agreement demonstrates that terrestrial plant material picked from the Lake Suigetsu sediment provides a reliable archive of atmospheric 14C, and therefore supports the site as being capable of providing a high-resolution extension to the “wholly terrestrial” (i.e. non-reservoir-corrected) calibration curve beyond its present 12,550 cal BP limit.