Radiocarbon measurement of CO2 from carbonate minerals using a gas ion source with an open split interface
Mr Brett Longworth1, Mr Joshua Burton1, Dr. Simon Pendleton1, Mr. Joshua Hlavenka1, Ms. Sydney Moser2, Dr. Mark Roberts1, Dr. Mark Kurz1
1Woods Hole Oceanographic Institution, Woods Hole, United States, 2University of Ottawa, Ottawa, Canada
We have developed a method for measurement of radiocarbon in carbonate minerals as CO2 gas via a NEC MCSNICS hybrid sputter gas ion source (HGIS). The method uses helium as a carrier gas to displace CO2 from sample vials to an open split, where a glass capillary samples the mixture for delivery directly to the HGIS. This method skips the gas transfer and quantification steps used in a closed inlet HGIS system, simplifying sample measurement. Samples larger than 10 mg carbonate can currently be measured. Results from measurements of consensus standards (TIRI-I, IAEA C2, and an internal modern shell standard), and samples from a marine core (40-115 pMC) show that the method agrees well with traditional AMS measurement of the same samples as graphite, and that the method error is less than 1.5 pMC. We discuss advantages and disadvantages of continuous flow sample introduction, and the effect of reduced precision on calibrated age-depth models produced using gas-source data.
I am a research associate at the National Ocean Sciences AMS (NOSAMS) facility at the Woods Hole Oceanographic Institution. I operate, maintain and develop the AMS systems at NOSAMS, develop new analysis methods, and work with radiocarbon data for quality control and carbon cycle research. I occasionally spend time at sea gathering samples, and I teach programming for reproducible data science.