Radiocarbon calibration curve spanning 0 to 50,000 years BP based on paired 230Th/234U/238U and 14C dates on pristine corals

Abstract

Radiocarbon dating is the most widely used dating technique in the world. Recent advances in Accelerator Mass Spectrometry (AMS) and sample preparation techniques have reduced the sample-size requirements by a factor of 1000 and decreased the measurement time from weeks to minutes. Today, it is estimated that more than 90 percent of all measurements made on accelerator mass spectrometers are for radiocarbon age dates. The production of 14 C in the atmosphere varies through time due to changes in the Earth's geomagnetic field intensity and in its concentration, which is regulated by the carbon cycle. As a result of these two variables, a radiocarbon age is not equivalent to a calendar age. Four decades of joint research by the dendrochronology and radiocarbon communities have produced a radiocarbon calibration data set of remarkable precision and accuracy extending from the present to approximately 12,000 calendar years before present. This paper presents high precision paired 230 Th/ 234 U/ 238 U and 14 C age determinations on pristine coral samples that enable us to extend the radiocarbon calibration curve from 12,000 to 50,000 years before present. We developed a statistical model to properly estimate sample age conversion from radiocarbon years to calendar years, taking full account of combined errors in input ages and calibration uncertainties. Our radiocarbon calibration program is publicly accessible at: http://www.radiocarbon.LDEO.columbia.edu/ along with full documentation of the samples, data, and our statistical calibration model. r

Comment on “Radiocarbon calibration curve spanning 0 to 50,000 years BP based on paired 230Th/234U/238U and 14C dates on pristine corals” by R.G. Fairbanks et al. (Quaternary Science Reviews 24 (2005) 1781–1796)☆☆doi of original article: 10.1016/j.quascirev.2005.04.007 and “Extending the radiocarbon calibration beyond 26,000 years before present using fossil corals” by T.-C. Chiu et al. (Quaternary Science Reviews 24 (2005) 1797–1808)☆☆☆☆doi of original article: 10.1016/j.quascirev.2005.04.002

“…In figure (1) of the Fairbanks et al (2005) paper, they present a variety of radiocarbon records and imply that this is the current status of data suitable for estimating the radiocarbon calibration curve, although many of the data sets shown in their plot did not meet the criteria established by the IntCal Working Group (Reimer et al 2002). In Figure 1 we show the data sets actually used to derive the IntCal04 or Marine04 calibration curves.…”

“…The scatter may in some cases be due to inadequate screening or pretreatment methods, while the offsets are likely due to poorly determined calendar ages or reservoir corrections. Fairbanks et al (2005) and Chiu et al (2005) argue that their new coral based radiocarbon record is sufficiently well dated and robust that they can exclude all these other data sets to prepare a precise and accurate radiocarbon calibration for the period between 12,000 and 50,000 cal BP. They argue that for all other data sets except tree-rings and corals, the calendar age dating is too poorly determined to be used for calibration.…”

“…Also at issue is the conversion of the coral-based calibration curve to an atmospheric curve where large inter-annual variability in the sea-surface age reservoir age has been observed in the southwest Pacific where one of two sets of corals used were sampled. In addition we comment on the seemingly ad hoc statistical methods utilized by Fairbanks et al (2005) to construct their curve. We recognize the value of the Fairbanks et al (2005) coral radiocarbon data set, but reassert the need for multiple, independently derived data to provide confirmation and validation to all radiocarbon calibration data.…”

“…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). 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.…”

“…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.…”