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| Titel |
An automated GC-C-GC-IRMS setup to measure palaeoatmospheric δ13C-CH4, δ15N-N2O and δ18O-N2O in one ice core sample |
| VerfasserIn |
P. Sperlich, C. Buizert, T. M. Jenk, C. J. Sapart, M. Prokopiou, T. Röckmann, T. Blunier |
| 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 ; 6, no. 8 ; Nr. 6, no. 8 (2013-08-13), S.2027-2041 |
| Datensatznummer |
250085036
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| Publikation (Nr.) |
 copernicus.org/amt-6-2027-2013.pdf |
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| Zusammenfassung |
| Air bubbles in ice core samples represent the only opportunity to study the
mixing ratio and isotopic variability of palaeoatmospheric CH4 and
N2O. The highest possible precision in isotope measurements is required
to maximize the resolving power for CH4 and N2O sink and source
reconstructions. We present a new setup to measure δ13C-CH4, δ15N-N2O and δ18O-N2O isotope ratios in one ice core sample and with one single
IRMS instrument, with a precision of 0.09, 0.6 and 0.7‰, respectively, as
determined on 0.6–1.6 nmol CH4 and 0.25–0.6 nmol N2O. The isotope
ratios are referenced to the VPDB scale (δ13C-CH4), the
N2-air scale (δ15N-N2O) and the VSMOW scale (δ18O-N2O). Ice core samples of 200–500 g are melted while the air
is constantly extracted to minimize gas dissolution. A helium carrier gas
flow transports the sample through the analytical system. We introduce a new
gold catalyst to oxidize CO to CO2 in the air sample. CH4 and
N2O are then separated from N2, O2, Ar and CO2 before
they get pre-concentrated and separated by gas chromatography. A combustion
unit is required for δ13C-CH4 analysis, which is equipped
with a constant oxygen supply as well as a post-combustion trap and a
post-combustion GC column (GC-C-GC-IRMS). The post-combustion trap and the
second GC column in the GC-C-GC-IRMS combination prevent Kr and N2O
interferences during the isotopic analysis of CH4-derived CO2.
These steps increase the time for δ13C-CH4 measurements,
which is used to measure δ15N-N2O and δ18O-N2O first and then δ13C-CH4. The analytical
time is adjusted to ensure stable conditions in the ion source before each
sample gas enters the IRMS, thereby improving the precision achieved for
measurements of CH4 and N2O on the same IRMS. The precision of our
measurements is comparable to or better than that of recently published
systems. Our setup is calibrated by analysing multiple reference gases that
were injected over bubble-free ice samples. We show that our measurements of
δ13C-CH4 in ice core samples are generally in good
agreement with previously published data after the latter have been
corrected for krypton interferences. |
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