vertical profiles of trapped greenhouse gases in alaskan permafrost active layers before the spring...
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Vertical Profiles of Trapped Greenhouse Gases in Alaskan Permafrost Active Layers Before the Spring ThawEunji Byun1, Ji-woong Yang1, Yongwon Kim2 and Jinho Ahn1
1School of Earth and Environmental Science, Seoul National University (SNU), Seoul, Korea2International Arctic Research Center (IARC), University of Alaska Fairbanks, Alaska, U.S.A.
CO2
CH4
Unfrozen SoilswithActivated CarbonActive
Frozen SoilswithStable Carbon Unactive
Modified from French (2007)
Increase of active partand decomposable carbons Amount and timing?
Atmospheric
GHGs
Soil GHGs can be transported by diffusion, ebullition and plant-mediated ways.• Can these processes always push GHGs
out from subsurface to the atmosphere?
Active layer freezes and thaws repeti-tively.• What if the active layer forms temporal
barriers to escape of GHGs?
Amount?
Timing?
The fate of GHGs under the active layer?
Trapped or Released
Depending on the permeabilityof surrounding soils
Instantly or More longer
Trapped ReleasedAccumulated Emitted at once
e.g. CH4 burst during transitional seasonsMastepanov et al. (2008); Song et al. (2012);
Chang et al. (2014)
TS: tundra vegetation
NY, SY and CR*: black spruce forests*fire burned in 2010
PF: peat mosses
Temperature logger
Drilling a frozen soil core
29 April 2013 – 10 May 2013 by Ji-woong Yang, Jinho Ahn and Yongwon Kim
Latitudinal variation along Alaskan highway
-27℃7.6 cm in
diameter and~90 cm long
Visual description on samples
Cut!
Cut!
Cut!
Cut!
Drilling soil coresbefore spring thaw Trapped gas extraction
from frozen soil samples(Headspace method)
NaCl saturated 10 mL
Left at 65℃for 30 min
Shaken over 2 min
(Kim et al., 2012; RESTEK, 2000)
Frozen
Thawed
CH4
CO2
CO2 and CH4 concentration measurements
7890A GC system with FID
and TCDAgilent
Technologies
Vertical profiles of measured values:(1) two peak CH4 results (PF and TS)(Byun et al. in
preparation)
Vertical pro-files of mea-sured val-ues:(2) results ofthree non-peak CH4 cases(NY, SY and CR)
(Byun et al. in preparation)
δ13CCH4
δDCH
4
Site Depth (cm) C1/C2 CH4 (ppmv*) (‰) (‰)
PF 72 1544 1390.0 -62.5 n.a.
TS 27 2083 6040.0 -63.0 n.a.
TS 81 3323 10300.0 -68.7 -206.6
*methane parts per million by volume (ppmv) of headspace (HS) gasn.a.: not available due to low concentration and/or limited sample volume
“CD-diagram for classification of bacterial and thermogenic natural gas
by the combination of δ13CCH4 and δDCH4 information.”
(Figure 4: Whiticar, 1999)
“Natural gas interpretative (“Bernard”) diagram combining
the molecular and isotope compositional information.” (Figure 12: Whiticar, 1999)
BacterialCarbonateReduction
Microbial oxidation
The trapped CH4?
All those three peak CH4 can be told to be generated microbially in soils by its isotopic information.
The measured amounts are not likely from instant production for just a few days. ( winter production or residuals from last summer)(Elberling et al., 2011; Lee et al., 2012)
Those were only extracted when the surrounding soils physically collapsed.
Temperature logger installed
Permafrost (perennially cryotic)
Active layer (seasonally frozen)
The fate of trapped CH4?
Downward thawing Downward freezing
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CH4
CH4
CH4
CH4
CO2
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CH4
CH4
CH4
Next summerThis winter
CH4
CH4
CH4
CH4
CH4
CH4
CH4 CO2
CO2
CH4
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The fate of trapped CH4 under frozen active layer?Inter-annually varied active layer thicknesses!
Shallower A.L.
Deeper A.L.
A.L. this year
Physical, chemical and biological factors of active layer soils can affect its formation and transportation.• Production can be influenced by nutritional levels,
microbial communities and temperatures.• Transportation can be inhibited by physical barriers
seasonally or even permanently depending on thaw range.Whether this phenomenon can be broad to some
other permafrost soils needs to be more investigated.• High levels of trapped CH4 were found from only 2
out of 5 soil cores in this study.• It can be improved by such a detailed subsurface
profiles accompanied by relevant efflux measurements at surface.
(Summary) Trapped CH4 under frozen active layer?
Any Questions and Comments:
Thank you all for being here andespecially Dona to bring me here
2015 EGU BG2.3“Vertical profiles of trapped greenhouse gases in Alaskan permafrost active layers before the spring thaw”