class7_w08

class7_w08 - Methane levels - 7.66 mm absorption band -...

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Methane levels - 7.66 μ m absorption band - about 2.5-fold increase since 1800 - leveling off since 1999 is not well understood (Bousquet et al., Nature 443 , 439 (2006); Wuebbles & Hayhoe, Earth-Sci Rev . 57, 177-210 (2002)) Chief atmospheric sink for methane : CH 4 + ·OH ·CH 3 + H 2 O (residence time ~ 12 years)
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Sources of methane – anthropogenic and natural Natural sources Anthropogenic sources Approximate overall estimates Natural : 140-235 Tg CH 4 /yr Agriculture : 141 Tg CH 4 /yr Anthro, non-Ag : 217 Tg CH 4 /yr What is the ultimate origin of CH 4 ? “marsh gas”
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Methanococcus jannaschii Strict anaerobe Optimal growth temperature = 85°C Autotrophic, nitrogen fixer 4H 2 + CO 2 CH 4 + 2H 2 O (ΔG = -131 kJ/mol) Exclusively hydrogenotrophic Central role in global carbon cycling “black smoker chimney” East Pacific Rise Methanogens account for 70% of the total global methane source
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Methanogenesis Hmd/Mtd
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Schimel J, PNAS 101 , 12400 (2004) microbial ecology industrial emissions Competition between methanogens and sulfate reducing archaebacteria, for nutrients in anaerobic environments, is affected by sulfur emissions. In turn, levels of atmospheric methane are affected.
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class7_w08 - Methane levels - 7.66 mm absorption band -...

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