High-precision dual-inlet IRMS measurements of the stable isotopes of CO₂ and the N₂O/CO₂ ratio from polar ice core samples Public Deposited

http://ir.library.oregonstate.edu/concern/articles/xd07gv786

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  • An important constraint on mechanisms of past carbon cycle variability is provided by the stable isotopic composition of carbon in atmospheric carbon dioxide (δ¹³C-CO₂) trapped in polar ice cores, but obtaining very precise measurements has proven to be a significant analytical challenge. Here we describe a new technique to determine the δ¹³C of CO₂ at very high precision, as well as measuring the CO₂ and N₂O mixing ratios. In this method, ancient air is extracted from relatively large ice samples (~400 g) with a dry-extraction “ice grater” device. The liberated air is cryogenically purified to a CO₂ and N₂O mixture and analyzed with a microvolume-equipped dual-inlet IRMS (Thermo MAT 253). The reproducibility of the method, based on replicate analysis of ice core samples, is 0.02‰ for δ¹³C-CO₂ and 2 ppm and 4 ppb for the CO₂ and N₂O mixing ratios, respectively (1σ pooled standard deviation). Our experiments show that minimizing water vapor pressure in the extraction vessel by housing the grating apparatus in a ultralow-temperature freezer (-60°C) improves the precision and decreases the experimental blank of the method to -0.07 ± 0.04‰. We describe techniques for accurate calibration of small samples and the application of a mass-spectrometric method based on source fragmentation for reconstructing the N₂O history of the atmosphere. The oxygen isotopic composition of CO₂ is also investigated, confirming previous observations of oxygen exchange between gaseous CO₂ and solid H₂O within the ice archive. These data offer a possible constraint on oxygen isotopic fractionation during H₂O and CO₂ exchange below the H₂O bulk melting temperature.
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  • Bauska, T. K., Brook, E. J., Mix, A. C., & Ross, A. (2014). High-precision dual-inlet IRMS measurements of the stable isotopes of CO₂ and the N₂O/CO₂ ratio from polar ice core samples. Atmospheric Measurement Techniques, 7(11), 3825-3837. doi:10.5194/amt-7-3825-2014
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  • description.provenance : Submitted by Erin Clark (erin.clark@oregonstate.edu) on 2015-01-16T00:33:03Z No. of bitstreams: 2 license_rdf: 1370 bytes, checksum: cd1af5ab51bcc7a5280cf305303530e9 (MD5) BauskaThomasCEOASHighPrecisionDual.pdf: 622051 bytes, checksum: 3b1441ecd5aacc7f192179acda961290 (MD5)
  • description.provenance : Made available in DSpace on 2015-01-16T00:33:23Z (GMT). No. of bitstreams: 2 license_rdf: 1370 bytes, checksum: cd1af5ab51bcc7a5280cf305303530e9 (MD5) BauskaThomasCEOASHighPrecisionDual.pdf: 622051 bytes, checksum: 3b1441ecd5aacc7f192179acda961290 (MD5) Previous issue date: 2014-11-19
  • description.provenance : Approved for entry into archive by Erin Clark(erin.clark@oregonstate.edu) on 2015-01-16T00:33:23Z (GMT) No. of bitstreams: 2 license_rdf: 1370 bytes, checksum: cd1af5ab51bcc7a5280cf305303530e9 (MD5) BauskaThomasCEOASHighPrecisionDual.pdf: 622051 bytes, checksum: 3b1441ecd5aacc7f192179acda961290 (MD5)

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