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Improved Precision of Radiocarbon Measurements for CH4 and CO2 Using GC and Continuous-Flow AMS Achieved by Summation of Repeated Injections

Published online by Cambridge University Press:  09 February 2016

Cameron P McIntyre ,
Ann P McNichol ,
Mark L Roberts ,
Jeffrey S Seewald ,
Karl F von Reden  and
William J Jenkins
Cameron P McIntyre*
Affiliation:
Dept. of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts, USA Laboratory of Ion Beam Physics, ETH Zurich, Switzerland
Ann P McNichol
Affiliation:
NOSAMS, Dept. of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts, USA
Mark L Roberts
Affiliation:
NOSAMS, Dept. of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts, USA
Jeffrey S Seewald
Affiliation:
Dept. of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts, USA
Karl F von Reden
Affiliation:
NOSAMS, Dept. of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts, USA
William J Jenkins
Affiliation:
Dept. of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts, USA NOSAMS, Dept. of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts, USA
*
Corresponding author. Email: mcintyre@phys.ethz.ch.
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Abstract

Compound specific radiocarbon measurements can be made instantaneously using a gas chromatograph (GC) combustion system coupled to a 14C AMS system fitted with a gas ion source. Samples below 10 μg C can be analyzed but the precision is reduced to 5–10% because of lower source efficiency. We modified our GC for CH4 and CO2 analysis and injected samples multiple times to sum data and increase precision. We attained a maximum precision of 0.6% for modern CO2 from 25 injections of 27 μg C and a background of ≃0.5% (40 kyr) for ancient methane. The 14C content of dissolved CO2 and CH4 in water samples collected at a deep-sea hydrothermal vent and a serpentine mud volcano was measured and the results for the vent sample are consistent with previously published data. Further experiments are required to determine a calibration and correction procedure to maximize accuracy.

Type
Articles
Information
Radiocarbon , Volume 55 , Issue 2: Proceedings of the 21st International Radiocarbon Conference (Part 1 of 2) , 2013 , pp. 677 - 685
Copyright
Copyright © 2013 by the Arizona Board of Regents on behalf of the University of Arizona 

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