A new approach to process planktonic foraminifera for radiocarbon measurements

foraminifera and corals, requires the extraction of about 1 mg C (10 mg CaCO3). Most laboratories prepare samples by decomposition of carbonates by phosphoric acid in evacuated glass tubes, with the formed CO2 requiring further cleaning and conversion to graphite, the entire process being time consuming. We tested a new approach for a simplified acid decomposition of carbonates with the Carbonate Handling System IonPlus+ using radiocarbon-free samples as blanks (Reference Material for Contemporary Modern Carbon-14, NIST 4990c Oxalic Acid II) and IAEA standards (IAEA-C1 Marble and IAEA-C2 Travertine) after dissolution with phosphoric acid and graphitization by the AGE as unknowns. Radiocarbon measurements of the reference carbonate materials were very well reproduced and in agreement with their consensus values. A comparison of the results with the new set up with the Carbonate Handling System IonPlus+ and the AGE system did not show any significant difference between 30 and 60 minutes acid decomposition time. Monospecific planktonic foraminifera (Globigerinoides inflata and Globigerinoides ruber; size ˃250 μm diameter) from the deep Mediterranean Sea were pretreated similarly following a 30 min dissolution time with the new system. Radiocarbon measurements, reported as percent Modern Carbon (pMC), were accomplished with the AMS system MICADAS at the Centro Nacional de Acceleradores (CNA, Seville), and dates are reported as conventional 14C age to obtain the reservoir-corrected age. Calibration of radiocarbon dates was undertaken using the Marine13 radiocarbon calibration curves. Some age uncertainties remain due to possible reworking of foraminifer shells, as well as large and variable reservoir effects within the Mediterranean Sea.