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| Titel |
Methane isotopic signature of gas bubbles in permafrost winter lake ice: a tool for quantifying variable oxidation levels |
| VerfasserIn |
C. J. Sapart, T. Boereboom, T. Roeckmann, J.-L. Tison |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250065676
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| Zusammenfassung |
| Methane (CH4) is a strong greenhouse gas and its atmospheric mixing ratio has strongly
increased since pre-industrial times. This increase was primarily due to emissions from
anthropogenic sources, but there is growing concern about possible feedbacks of natural
sources in a changing climate. Thawing of permafrost areas in the Arctic is considered as an
important feedback, since the Arctic region undergoes the fastest climate change and
hosts large carbon stocks. Subarctic lakes are considered as “hotspots” for CH4
emissions, but the role of the ice cover during the winter period is not well understood to
date.
Here, we present measurements of CH4 mixing ratio and δ13C-CH4 in 4 types of bubbles
identified in subarctic lake ice covers located in a sporadic or discontinuous permafrost area.
Our analysis reveals that different bubble types contain CH4 with different, specific isotopic
signatures. The evolution of mixing ratio and δ13C-CH4 suggest that oxidation of dissolved
CH4 is the most important process determining the isotopic composition of CH4 in
bubbles. This results from gas exsolution occurring during the ice growth process.
A first estimate of the CH4 oxidation budget (mean = 0.12 mg CH4 m-2 d-1)
enables to quantify the impact of the ice cover on CH4 emissions from subartic
lakes.
The increased exchange time between gases coming from the sediments and the
water column, due to the capping effect of the lake ice cover, reduces the amount of
CH4 released “as is” and favours its oxidation into carbon dioxide; the latter being
further added to the HCO3- pool through the carbonate equilibration reactions. |
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