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Atmospheric Methane: How well can we apportion present sources and predict future changes?. William S. Reeburgh Earth System Science University of California Irvine [email protected]. Wahlen , 1993. Geochemical Approaches. Four R’s of Geochemistry (Dayton Carritt) Routes Rates - PowerPoint PPT Presentation
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Atmospheric Methane: How well Atmospheric Methane: How well can wecan we apportion present sources apportion present sources and predictand predict future changes? future changes?
William S. ReeburghWilliam S. Reeburgh
Earth System ScienceEarth System Science
University of California IrvineUniversity of California Irvine
[email protected]@uci.edu
Wahlen, 1993
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GeochemicalGeochemical ApproachesApproaches
• Four R’s of GeochemistryFour R’s of Geochemistry (Dayton Carritt)(Dayton Carritt)• RoutesRoutes• Rates Rates • ReactionsReactions • ReservoirsReservoirs
• Inverse Chemical EngineeringInverse Chemical Engineering (W. S. Broecker) (W. S. Broecker) Considers Earth as a chemical plant with no blueprints. Task of Considers Earth as a chemical plant with no blueprints. Task of geochemistry is to produce the missing blueprints with measurements of geochemistry is to produce the missing blueprints with measurements of concentrations, fluxes, reaction rates, etc. concentrations, fluxes, reaction rates, etc.
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Rate MeasurementsRate Measurements
Flux MeasurementsFlux Measurements (chamber, eddy (chamber, eddy flux)flux)
Sulfate Reduction Sulfate Reduction 3535SOSO44
-2-2 H H223535S (1.4 Ci S (1.4 Ci
mmolemmole-1-1) ) (carrier-free)(carrier-free)
Methane OxidationMethane Oxidation Aerobic and AnaerobicAerobic and Anaerobic
Carbon (Carbon (1414C)C) 1414C-CHC-CH44 1414COCO2 2 (55 (55 mCi mmolmCi mmol-1-1))
Hydrogen (Hydrogen (33H)H) 33H-CHH-CH4 4 33HH220 (3 0 (3 Ci mmolCi mmol-1-1))
Methane SourcesMethane Sources
MicrobialMicrobial
Competitive substrates (anoxic Competitive substrates (anoxic conditions)conditions) COCO22 reduction reduction COCO22 + 4H + 4H22 CH CH44 + 2H + 2H22O O
Acetate fermentationAcetate fermentation CHCH33COOH CHCOOH CH44 + CO + CO22
Non-competitive substrates (oxic Non-competitive substrates (oxic conditions?)conditions?) Methylated Compounds Methylated Compounds (methylamines, DMS, DMDS, (methylamines, DMS, DMDS, methane thiol, methane thiol, methyl phosphonate)methyl phosphonate)
Methane SourcesMethane Sources
AbioticAbiotic “ “Serpentinization Reaction”Serpentinization Reaction”
6[(Mg6[(Mg1.51.5FeFe0.50.5)SiO)SiO44] + 7H] + 7H22O O olivineolivine
3[Mg3[Mg33SiSi22OO55(OH)(OH)44] + ] + FeFe33OO44 + H + H22
serpentineserpentine magenetitemagenetite
and and
COCO22 + 4H + 4H22 (300 C, 500bar)(300 C, 500bar) CH CH44 + 2H + 2H22OO
“ “Thermal Cracking”, PyrolysisThermal Cracking”, Pyrolysis
1414CHCH44 added by PWR’s added by PWR’s
Methane Sinks
Microbial Aerobic Oxidation 2CH2CH44 + O + O2 2 2CO2CO2 2 + 2H+ 2H2200
(decreases pH, dissolves (decreases pH, dissolves carbonates)carbonates)
Anaerobic Oxidation (AOM or AMO)(AOM or AMO) CHCH44 + SO + SO44
-2 -2 HCO HCO33-- + HS + HS--
+ H+ H2200 (increases alkalinity; (increases alkalinity; isotopically light isotopically light carbonates precipitate.)carbonates precipitate.)
““Reverse Methanogenesis”Reverse Methanogenesis” CHCH44 + 2H2H220 CO0 CO2 2 + 4H+ 4H22
Methane SinksMethane Sinks
Photochemical Oxidation Photochemical Oxidation (principal atmospheric sink)(principal atmospheric sink)
OO33 + h + h O( O(11D) + OD) + O22 = 315 nm= 315 nm
O(O(11D) + HD) + H22O 2OHO 2OH
CHCH44 + OH H + OH H220 + CH0 + CH33
Cicerone & Oremland, 1988
Methane budget is well-constrained. Methane budget is well-constrained. We know the total well, but We know the total well, but individual source terms are individual source terms are uncertain to a factor of 2 or more. uncertain to a factor of 2 or more. A “bird’s eye” budget; considers net A “bird’s eye” budget; considers net additions to the atmosphere. A net additions to the atmosphere. A net atmospheric budget.atmospheric budget.
We can consider consumption or We can consider consumption or oxidation, but the previous oxidation, but the previous constraints do not apply. Oxidation constraints do not apply. Oxidation before emission to atmosphere has a before emission to atmosphere has a large effect.large effect.
InversionsInversions
Fung et al., 1997, JGR
Hein et al., 1997, GBC
Mikalof-Fletcher et al., 2004, GBC (CH4 & 13C-CH4)
Butler et al., 2005, JGR
Van der Werf et al., 2004, Science (wildfire contributions)
Bousquet et al., 2000, Nature
Recently Reported CHRecently Reported CH44 Sources Sources
Aerobic Methane Production by PlantsAerobic Methane Production by Plants
Siberian thaw lakes/Yedoma soilsSiberian thaw lakes/Yedoma soils
*Ocean Vent Additions: CH*Ocean Vent Additions: CH44-consuming benthic-consuming benthic communitiescommunities
*Methane Clathrate Hydrate, Mud Volcano Additions*Methane Clathrate Hydrate, Mud Volcano Additions
*Large “Fossil CH*Large “Fossil CH44” Additions to Anoxic Basins & Ocean” Additions to Anoxic Basins & Ocean
**oxidized in ocean; not emitted to atmosphereoxidized in ocean; not emitted to atmosphere
Aerobic ProductionAerobic Production
Aerobic ProductionAerobic Production
AerobicAerobic Production?Production?
Aerobic Production?Aerobic Production?
Siberian thaw lakes/Yedoma soilsSiberian thaw lakes/Yedoma soils
Siberian thaw lakes/Yedoma soilsSiberian thaw lakes/Yedoma soils
Lost City Hydrothermal FieldLost City Hydrothermal Field
Kelley Kelley et al.et al. (2005) (2005)Boetius (2005)Boetius (2005)
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Treude et al., 2003Treude et al., 2003
Michaelis Michaelis et al.et al. (2002) (2002)
3 - 4 m height3 - 4 m height
5 5 mm
Boetius Boetius et al.et al. (2000) (2000)
Clathrate HydratesClathrate Hydrates
Mud VolcanoesMud Volcanoes
http://www.crimea-info.orghttp://www.crimea-info.org
Fossil CHFossil CH44 Additions Additions
Cariaco BasinCariaco Basin
Fossil CHFossil CH44 Additions Additions
Black SeaBlack Sea
Future WorkFuture Work
Add Add 22H-CHH-CH44 and and 1313C-CHC-CH44 to NOAA time to NOAA time seriesseries
Natural hydrate dissociation rate?Natural hydrate dissociation rate?
More ocean measurements of natural More ocean measurements of natural 1414CHCH44
Ocean mixed layer maximum?Ocean mixed layer maximum?
Identify/isolate anaerobic methane Identify/isolate anaerobic methane oxidizer(s)oxidizer(s)
Determine determine mechanism for Determine determine mechanism for anaerobicanaerobic oxidizer(s). oxidizer(s).
ResourcesResources
(2003) In Vol. 4 (The Atmosphere) Treatise on Geochemistry(2003) In Vol. 4 (The Atmosphere) Treatise on Geochemistry , Eds. Turekian and Holland,, Eds. Turekian and Holland, Elsevier-Pergamon, Oxford. 2003 (2006 update for on-line version)Elsevier-Pergamon, Oxford. 2003 (2006 update for on-line version)
AcknowledgementsAcknowledgements
Support:Support: NSF Ocean SciencesNSF Ocean Sciences W. M. Keck Foundation - MS & AMSW. M. Keck Foundation - MS & AMS
Students:Students: David Heggie - Australian. Geol. Survey Org.David Heggie - Australian. Geol. Survey Org. Marc Alperin - UNC Chapel HillMarc Alperin - UNC Chapel Hill Jennifer King - Univ. of MinnesotaJennifer King - Univ. of Minnesota David Valentine - UC Santa BarbaraDavid Valentine - UC Santa Barbara John Kessler - Princeton postdocJohn Kessler - Princeton postdoc Mary Pack - UCI currentMary Pack - UCI current
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Clathrate HydratesClathrate Hydrates
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Approaches to Estimating the Clathrate-Derived
Methane Flux to the Ocean
Global Methane Budget SinksGlobal Methane Budget Sinks
Aerobic oxidation of methaneAerobic oxidation of methane 2CH2CH44 + O + O2 2 2CO2CO2 2 + 2H+ 2H2200
(decreases pH, dissolves carbonates)(decreases pH, dissolves carbonates)
Anaerobic oxidation of methane (AOM or AMO)Anaerobic oxidation of methane (AOM or AMO) CHCH44 + SO + SO44
-2 -2 HCO HCO33-- + HS + HS-- + H + H2200
(increases alkalinity; carbonates w/light(increases alkalinity; carbonates w/light isotopic signature ppt.)isotopic signature ppt.)