Abstract
ABSTRACTEarly researchers of radiocarbon levels in Southern Hemisphere tree rings identified a variable North-South hemispheric offset, necessitating construction of a separate radiocarbon calibration curve for the South. We present here SHCal20, a revised calibration curve from 0–55,000 cal BP, based upon SHCal13 and fortified by the addition of 14 new tree-ring data sets in the 2140–0, 3520–3453, 3608–3590 and 13,140–11,375 cal BP time intervals. We detail the statistical approaches used for curve construction and present recommendations for the use of the Northern Hemisphere curve (IntCal20), the Southern Hemisphere curve (SHCal20) and suggest where application of an equal mixture of the curves might be more appropriate. Using our Bayesian spline with errors-in-variables methodology, and based upon a comparison of Southern Hemisphere tree-ring data compared with contemporaneous Northern Hemisphere data, we estimate the mean Southern Hemisphere offset to be 36 ± 2714C yrs older.
Highlights
The conversion of terrestrial radiocarbon (14C) ages into calendar time requires a calibration curve that accurately reflects past atmospheric 14C levels
Paired decadal measurements made from contemporaneous British oak (Quercus petraea) and New Zealand (NZ) cedar (Libocedrus bidwillii) or silver pine (Manoao colensoi) tree rings from 1000–0 cal BP by Queen’s University Belfast and Waikato University, showed there were differences between the structural forms of the radiocarbon calibration curves for each hemisphere
There are some aspects of SHCal13 that have potentially important implications for SHCal20: 1. The value of 129 ± 14 BP from Pretoria for 100 cal BP (1850 CE) that was used in SHCal04 and SHCal13 is incorrect
Summary
The conversion of terrestrial radiocarbon (14C) ages into calendar time requires a calibration curve that accurately reflects past atmospheric 14C levels. Paired decadal measurements made from contemporaneous British oak (Quercus petraea) and New Zealand (NZ) cedar (Libocedrus bidwillii) or silver pine (Manoao colensoi) tree rings from 1000–0 cal BP by Queen’s University Belfast (identifier UB) and Waikato University (identifier Wk), showed there were differences between the structural forms of the radiocarbon calibration curves for each hemisphere They demonstrated that the N-S offset was not constant but varied with time, with a periodicity of approximately 130 cal yrs, and amplitudes ranging from 8–80 14C yrs (McCormac et al 1998a, 1998b; Hogg et al 2002). The other three Huon pine data sets (SRT-781, -782, and -783) have been omitted from SHCal
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