COMPARING DIRECT CARBONATE AND STANDARD GRAPHITE <sup>14</sup>C DETERMINATIONS OF BIOGENIC CARBONATES
Jordon Bright, Chris Ebert, Matthew A. Kosnik, John Southon, Katherine Whitacre, Paolo G. Albano, Carola Flores, Thomas K. Frazer, Quan Hua, Michał Kowalewski, Julieta Martinelli, David Oakley, Wesley Parker, Michael J. Retelle, Matias do Nascimento Ritter, Marcelo M. Rivadeneira, Daniele Scarponi, Yurena Yanes, Martin Zuschin, Darrell S. Kaufman
Abstract
ABSTRACT The direct carbonate procedure for accelerator mass spectrometry radiocarbon (AMS 14 C) dating of submilligram samples of biogenic carbonate without graphitization is becoming widely used in a variety of studies. We compare the results of 153 paired direct carbonate and standard graphite 14 C determinations on single specimens of an assortment of biogenic carbonates. A reduced major axis regression shows a strong relationship between direct carbonate and graphite percent Modern Carbon (pMC) values (m = 0.996; 95% CI [0.991–1.001]). An analysis of differences and a 95% confidence interval on pMC values reveals that there is no significant difference between direct carbonate and graphite pMC values for 76% of analyzed specimens, although variation in direct carbonate pMC is underestimated. The difference between the two methods is typically within 2 pMC, with 61% of direct carbonate pMC measurements being higher than their paired graphite counterpart. Of the 36 specimens that did yield significant differences, all but three missed the 95% significance threshold by 1.2 pMC or less. These results show that direct carbonate 14 C dating of biogenic carbonates is a cost-effective and efficient complement to standard graphite 14 C dating.