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| Titel |
Atmospheric methane isotope records during MIS 4 |
| VerfasserIn |
Todd Sowers, Michael Bock, Hailey Mitchell |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250092566
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| Publikation (Nr.) |
 EGU/EGU2014-8218.pdf |
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| Zusammenfassung |
| The long-term δ13CH4record has led to a new paradigm in our thinking of the biogeochemistry
of atmospheric CH4 (Möller et al. 2013). Throughout the last glacial period, abrupt D/O
CH4changes appear to be decoupled from δ13CH4, while for δDCH4 we are still missing the
big picture. The lack of a clear long-term relationship between loading changes and the
isotopic composition of atmospheric CH4suggests multiple sources/sinks were responsible
for the observed changes and/or that the characteristic isotope value for some of these sources
may have changed over time.
During the early part of MIS 4, we observed a ~4oincrease in δ13CH4during a period
when CH4changes were less than 50 ppb. We measured 12 ice core samples from the NEEM
core for δDCH4 covering DO 8 and the MIS 5-4 transition. These new δDCH4 data
compliment previously published δDCH4 data from EDML covering the same period (Möller
et al. 2013). Replicate analyses of NEEM ice from DO 8 agreed with previously measured
samples from NGRIP (Bock et al., 2010). External precision of the analyses based on
replicate air standards run throughout each analytical day were ±1.8oṪhese data were
overlain on previously measured δ13CH4data from the Vostok and EDML ice cores from the
same periods. The δ13CH4data for the MIS4 start at ~ -48oaround 75ka and increase to
-44oat 65ka and then decrease to -46oby 59ka. In contrast, NEEM δDCH4 values start at
-90oat 70ka and decrease to -97oat 64ka before increasing to -92oby 59ka.
These two records appear to be roughly in phase with one another but opposite in
the sign of their changes. Comparison between NEEM and EDML δDCH4 data
for MIS4 suggest the interpolar δDCH4 difference increases somewhat during the
δ13CH4transition.
We plan to discuss these records in terms of constraints on the biogeochemistry of
atmospheric methane during MIS 4.
Bock, M., J. Schmitt, L. Möller, R. Spahni, T. Blunier and H. Fischer (2010). "Hydrogen
Isotopes Preclude Marine Hydrate CH4 Emissions at the Onset of Dansgaard-Oeschger
Events." Science 328(5986): 1686-1689, 10.1126/science.1187651.
Möller, L., T. Sowers, M. Bock, R. Spahni, M. Behrens, J. Schmitt, H. Miller and H.
Fischer (2013). "Independent variations of CH4 emissions and isotopic composition over the
past 160,000 years." Nature Geoscience10.1038/ngeo1922. |
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