A new approach to process planktonic foraminifera for radiocarbon measurements

Abstract

Carbonate shells from foraminifera are often analyzed for radiocarbon to determine the age of deep-sea sediments or to assess radiocarbon reservoir ages. The Centro Nacional de Aceleradores (CNA) is equipped for the AMS radiocarbon analysis with a MICADAS (MIni CArbon DAting System), and a sample processing line including vial flushing, carbonate dissolution and transfer of the evolved CO2 from the septum sealed tubes to the automated graphitization equipment (AGE). In this work, we have tested a fullyautomated setup from sampling the released CO2 from small carbonate samples (i.e. foraminifera shells) for radiocarbon analysis, where the formed CO2 is later flushed by helium flow by means of a double-wall needle mounted from the tubes to the zeolite trap of the existing AGE-2. This carbonate dissociation line essentially replaces the elemental analyser normally used for the combustion of organic samples to further reduce the effort involved for sample preparation. The automated method yields in low sample blanks of about 50,000 years. Results of the processed reference materials (IAEA-C1 and IAEA-C2) are in agreement with their consensus values. Using this automated dissociation line we were able to date samples of monospecific foraminifera shells (~10 mg) of ~ 1000 radiocarbon years.