COMPARING DIRECT CARBONATE AND STANDARD GRAPHITE ¹⁴C DETERMINATIONS OF BIOGENIC CARBONATES

Abstract

The direct carbonate procedure for accelerator mass spectrometry radiocarbon (AMS 14C) 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 14C 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 14C dating of biogenic carbonates is a cost-effective and efficient complement to standard graphite 14C dating.

Chronology, time averaging, and oxygen isotope composition of harvested marine mollusk assemblages from Ifri Oudadane, northeast Morocco

“…However, the shells analyzed here did not show visual evidence of heat exposure, and further research is needed to evaluate the potential effects of diagenetic alteration in radiocarbon results. This work illustrates that the rapid and more affordable carbonate-target radiocarbon method proved to be a valid and reliable tool for calculating the age of Holocene archaeological shells, in agreement with previous studies testing the validity of the method and successfully applying it (e.g., Kowalewski et al, 2018;New et al, 2019;Bright et al, 2021).…”

“…The carbonate-target radiocarbon dating is approximately one-third the cost of traditional graphite-target radiocarbon dating. Moreover, for samples that are younger than 10,000 yr old, this method yields statistically indistinguishable results compared with the traditional graphite-target method (Bush et al, 2013;Bright et al, 2021). To test the potential radiocarbon offsets within different layers of the same shell, three shells were selected to assess whether or not the outer and inner aragonitic portion of the same shell would yield statistically equivalent radiocarbon ages.…”

Native biodiversity collapse in the eastern Mediterranean

“…We focused on three native bivalve species that were still extant in the study area. Shells were dated by accelerator mass spectrometry (AMS), using powdered carbonate targets [23,24]. The 149 obtained radiocarbon ages were converted to calendar ages.…”

Non‐indigenous molluscs in the Eastern Mediterranean have distinct traits and cannot replace historic ecosystem functioning

“…To enable a rigorous temporal interpretation of the ecological information extracted from time-averaged death assemblages, we quantified their shell age distributions by radiocarbon dating (see Albano et al, 2021). At each station, we dated 10 to 15 valves of common native bivalve species that were also recorded alive in our samples (see Supporting Information Table S1.2 for further details and a list of dated species), using accelerator mass spectrometry (AMS) of powdered carbonate targets (Bright et al, 2021;Bush et al, 2013). Ages are reported in calendar years before the year of sample collection.…”