4:30 PM - 4:45 PM
[MIS02-09] A mechanism for non-linear amplification of methane flux in the early Earth system with primitive biosphere
Keywords:Archean, Atmospheric photochemical model, Marine microbial ecosystem, Faint young Sun paradox, Earth-like exoplanet
Here, we investigate the mechanism for non-linear amplification of CH4 flux by detailed analysis with a coupled model of atmospheric photochemistry and marine ecosystem. We found that the difference between the two cases is derived from difference in redox balance at the same outgassing flux of H2. A net flux of reducing power increases with activity of Fe-using anoxygenic photoautotrophs. Two positive feedbacks for the production of H2 and CO, strongly impact on the CH4 flux and concentrations. Biogenic CH4 is converted back to H2 and CO by photolysis in the atmosphere, which are recycled by marine microbial ecosystem, forming organic matters followed by decomposition to produce CH4 again. That is, increase of H2 and CO concentrations owing to photolysis of CH4 in the atmosphere triggers positive feedback of CH4 flux. Increase of H2 concentration increases linearly, while CO concentration increases non-linearly with an increase in the CH4 flux. This result indicates that positive feedback with CO should contribute to amplification for CH4 flux more stronger than the positive feedback with H2.
We will also discuss on application of this model to Earth-like exoplanets orbiting around stars with different masses and spectral types.