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| Titel |
A radiocarbon-based inventory of methane and inorganic carbon dissolved in surface lake waters in arctic Alaska, USA |
| VerfasserIn |
Claudia Czimczik, Elder Clayton, Xiaomei Xu, Jennifer Lehman, Amy Townsend-Small |
| 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 |
250094090
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| Publikation (Nr.) |
 EGU/EGU2014-9453.pdf |
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| Zusammenfassung |
| Major uncertainties in land-atmosphere carbon (C) exchange in the rapidly warming and
wetting Arctic are 1) the magnitude and timing of net losses of ancient permafrost C to the
atmosphere and 2) the relative changes of C exchange as carbon dioxide (CO2) or the more
powerful greenhouse gas methane (CH4). For CH4, the role of diffusive fluxes versus
plant-mediated and ebullition fluxes is poorly constrained. Radiocarbon (14C) is a unique
tracer for distinguishing ancient permafrost C from C rapidly cycling between the land and
atmosphere. In addition, stable isotope ratios (13C/12C and D/H) provide insight to trace gas
production and consumption pathways. Previous measurements, however, have focused on
CH4 from ebullition fluxes due to technical and logistical challenges in 14C-CH4
analysis.
We quantified the 14C content and δ13C signatures of dissolved CH4 and DIC in lake
surface waters along a north-south transect on the North Slope of Alaska, USA
(69.9°N to 71.28°N, -156.12°W to -156.32°W). Samples were collected at the end
of winter before ice break-up (April 2013) and during summer (August 2012 &
2013) in 1 L bottles. A subset of samples was also analyzed for CH4 and CO2
concentrations and stable isotope ratios by the Circumarctic Lakes Observation Network
(CALON). In addition, in August 2013, we measured the 14C content and δ13C
ratios of lake-atmosphere CH4 and CO2 exchange near Barrow, AK, USA (71°N,
-156°W). We obtained dissolved CH4 and CO2 sufficient for 14C analysis from lakes
with concentrations as low as 0.01 mg C /L) using a novel, in situ preconcentration
method (liqui-cel, Membrana). And, we measured and collected isoflux samples of
simulated, near-shore ebulltion-derived CH4 and CO2 using floating headspace
chambers.
Isotope samples were processed using a novel, flow-through vacuum line and analyzed at the
KCCAMS facility at the University of California, Irvine, USA with accelerator (0.5MV
1.5SDH-2, National Electrostatics Corporation) and isotope-ratio mass spectrometry (Gas
Bench coupled with Finnigan DeltaPlus, Thermo).
Preliminary data indicate that along the transect summertime DIC concentrations range from
112.4 μM to 1619.8 μM, with a 14C content of 0.87 FM to modern and δ13C ratios of -23.5
to +3.0 o. We found no relationship between 14C content and latitude, however regional
clusters of lakes had similar isotope signatures.
Summertime concentrations of dissolved CH4 were mostly below the analytical limit for 14C
analysis, except for one modern sample.
Within the Barrow region, summertime dissolved CH4 was depleted in 14C in lakes with
surface areas ≥8 ha, but modern in ponds |
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