Radiocarbon Calibration and Comparison to 50 Kyr BP with Paired ¹⁴C and ²³⁰Th Dating of Corals from Vanuatu and Papua New Guinea

Abstract

We calibrated portions of the radiocarbon time scale with combined 230Th, 231Pa, 14C measurements of corals collected from Espiritu Santo, Vanuatu and the Huon Peninsula, Papua New Guinea. The new data map 14C variations ranging from the current limit of the tree-ring calibration [11,900 calendar years before present (cal BP), Kromer and Spurk 1998, now updated to 12,400 cal B P, see Kromer et al., this issue], to the 14C-dating limit of 50,000 cal BP, with detailed structure between 14 to 16 cal kyr BP and 19 to 24 cal kyr BP. Samples older than 25,000 cal BP were analyzed with high-precision 231Pa dating methods (Pickett et al. 1994; Edwards et al. 1997) as a rigorous second check on the accuracy of the 230Th ages. These are the first coral calibration data to receive this additional check, adding confidence to the age data forming the older portion of the calibration. Our results, in general, show that the offset between calibrated and 14C ages generally increases with age until about 28,000 cal BP, when the recorded 14C age is nearly 6800 yr too young. The gap between ages before this time is less; at 50,000 cal BP, the recorded 14C age is 4600 yr too young. Two major 14C-age plateaus result from a 130 drop in Δ14C between 14–15 cal kyr BP and a 700 drop in Δ14C between 22–25 cal kyr BP. In addition, a large atmospheric Δ14C excursion to values over 1000 occurs at 28 cal kyr BP. Between 20 and 10 cal kyr BP, a component of atmospheric Δ14C anti-correlates with Greenland ice δ18O, indicating that some portion of the variability in atmospheric Δ14C is related to climate change, most likely through climate-related changes in the carbon cycle. Furthermore, the 28-kyr excursion occurs at about the time of significant climate shifts. Taken as a whole, our data indicate that in addition to a terrestrial magnetic field, factors related to climate change have affected the history of atmospheric 14C.

Comparison of 14C and U-Th Ages in Corals from IODP #310 Cores Offshore Tahiti

“…Tahiti data (red circles) have been corrected from a reservoir age of 300 yr . Comparison of the new results from Tahiti with the other corals data sets: Araki, Barbados, and Kirimati (dark blue triangles, Fairbanks et al 2005); Vanuatu and Papua New Guinea (gray diamonds, Cutler et al 2004); Barbados (light blue triangles), Tahiti, and Mururoa (green circles, Bard et al 1998). The error bars for 14 C ages and U-Th ages are given at the 2 level.…”

“…Still, marine archives present the advantage of covering the complete 14 C time window. In this respect, fossil corals have been regarded as one of the best candidates for extending the 14 C calibration because they are the most suitable material for combining high-accuracy and -precision U-Th dating and 14 C age measurements (Bard et al 1990a(Bard et al ,b, 1993Edwards et al 1993;Cutler et al 2004;Paterne et al 2004;Fairbanks et al 2005). This approach, however, is limited by the scarcity of adequate coral sequences that cover the 14 C timescale beyond the tree-ring records: corals that thrived during the last glaciation or during marine isotope stage 3 are now as much as 100 m below present sea level.…”

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

“…Because of the potential for coral alteration (especially of pre-LGM corals), the IntCal group has adopted a set of screening and pretreatment protocols which must be met for all coral data incorporated into the IntCal radiocarbon calibration, which (1998), Yokoyama et al (2000) , and Cutler et al (2004). In doing so, they neglected to clearly state that the data reported by Yokoyama et al (2000) did not meet quality criteria set by the IntCal group Reimer et al, 2002)) and were thus not selected for inclusion in the IntCal compilation Reimer et al, 2004).…”

Modern and Pleistocene Reservoir Ages Inferred from South Pacific Corals

“…There is no question about the source of carbon or where it was acquired. The calendar age of modern samples (up to 500 yr old) can be established directly by counting annual growth bands, and paleocorals can be accurately dated with U/Th and 231 Pa techniques (Edwards et al 1987;Cutler et al 2004). Corals are widespread and common throughout the South Pacific, and many live for decades to centuries, so very long records can be constructed, with annual to subannual resolution.…”