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| Titel |
High-precision dual-inlet IRMS measurements of the stable isotopes of CO2 and the N2O / CO2 ratio from polar ice core samples |
| VerfasserIn |
T. K. Bauska, E. J. Brook, A. C. Mix, A. Ross |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1867-1381
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Measurement Techniques ; 7, no. 11 ; Nr. 7, no. 11 (2014-11-19), S.3825-3837 |
| Datensatznummer |
250115954
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| Publikation (Nr.) |
 copernicus.org/amt-7-3825-2014.pdf |
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| Zusammenfassung |
| 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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