Radiocarbon calibration curves are essential for converting radiocarbon-dated chronologies to the calendar timescale. Prior to the 1980s numerous differently derived calibration curves based on radiocarbon ages of known age material were in use, resulting in "apples and oranges" comparisons between various records (Klein et al., 1982), further complicated by until then unappreciated inter-laboratory variations (International Study Group, 1982). The solution was to produce an internationally agreed calibration curve based on carefully screened data with updates at 4-6 year intervals (Klein et al., 1982; Stuiver and Reimer, 1986, 1993; Stuiver et al., 1998). The IntCal working group has continued this tradition with the active participation of researchers who produced the records that were considered for incorporation into the current, internationally ratified calibration curves, IntCal04, SHCal04, and Marine04, for Northern Hemisphere terrestrial, Southern Hemisphere terrestrial, and marine samples, respectively (Hughen et al., 2004; McCormac et al., 2004; Reimer et al., 2004). Fairbanks et al. (2005), accompanied by a more technical paper, Chiu et al. (2005), and an introductory comment, Adkins (2005), recently published a "calibration curve spanning 0-50,000 years". Fairbanks et al. (2005) and Chiu et al. (2005) have made a significant contribution to the database on which the IntCal04 and Marine04 calibration curves are based. These authors have now taken the further step to derive their own radiocarbon calibration extending to 50,000 cal BP, which they claim is superior to that generated by the IntCal working group. In their papers, these authors are strongly critical of the IntCal calibration efforts for what they claim to be inadequate screening and sample pretreatment methods. While these criticisms may ultimately be helpful in identifying a better set of protocols, we feel that there are also several erroneous and misleading statements made by these authors which require a response by the IntCal working group. Furthermore, we would like to comment on the sample selection criteria, pretreatment methods, and statistical methods utilized by Fairbanks et al. (2005) in derivation of their own radiocarbon calibration.
Bibliographical noteFunding Information:
The authors wish to thank S. Sépulcre for measuring the XRD spectra presented in Fig. 2 . We also wish to thank A. Mix for a thorough and critical review which resulted in improvements to this comment. A portion of the work on the IntCal04 project was funded by a grant from the Leverhulme Trust.