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Multiple Equilibria in Atmospheric Oxygen: Archean , Proterozoic , Phanerozoic .

Multiple Equilibria in Atmospheric Oxygen: Archean , Proterozoic , Phanerozoic . Tom Laakso & Dan Schrag Goldschmidt Geochemistry June 13, 2014. Multiple Equilibria in p O 2. Kump 2008. Multiple Equilibria model: Proterozoic / Phanerozoic 3-box ocean/atmosphere model

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Multiple Equilibria in Atmospheric Oxygen: Archean , Proterozoic , Phanerozoic .

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  1. Multiple Equilibria in Atmospheric Oxygen: Archean, Proterozoic, Phanerozoic. Tom Laakso & Dan Schrag Goldschmidt Geochemistry June 13, 2014

  2. Multiple Equilibria in pO2 Kump 2008

  3. Multiple Equilibria model: • Proterozoic / Phanerozoic • 3-box ocean/atmosphere model • oxygen, carbon, sulfur, iron cycles • first order kinetics • oxygen-sensitive organic carbon burial efficiency • oxygen-sensitive recycling of sedimentary P • oxygen-sensitive riverine P flux

  4. Multiple Equilibria model: Proterozoic / Phanerozoic Laakso & Schrag 2014

  5. The Great Oxidation Event Kump 2008

  6. hydrogen outgassing serpentinization Archeanredox budget: prebiotic world

  7. mantle hydrogen source Archeanredox budget: prebiotic world

  8. hydrogen escape mantle hydrogen source Archeanredox budget: prebiotic world

  9. hydrogen escape mantle hydrogen source chemoautotrophy: 2 H2 + CO2 H2O + CH2O Archeanredox budget: early life

  10. hydrogen escape mantle hydrogen source chemoautotrophy: 2 H2 + CO2 H2O + CH2O organic burial (< nutrient input) Archeanredox budget: early life

  11. hydrogen escape mantle hydrogen source oxygenic photosynthesis CH2O + O2 CO2 + H2O chemoautotrophy: 2 H2 + CO2 H2O + CH2O organic burial (< nutrient input) Archeanredox budget: oxygenic photosynthesis

  12. hydrogen escape oxidation: atmosphere mantle hydrogen source oxygenic photosynthesis CH2O + O2 CO2 + H2O chemoautotrophy: 2 H2 + CO2 H2O + CH2O oxidation: seafloor, aqueous, continental organic burial (< nutrient input) Archeanredox budget: oxygenic photosynthesis

  13. Archean equilibrium redox budget Hydrogen: Oxygen: mantle H2 source = nutrient source = hydrogen escape + aqueous & crustal oxidation + atmospheric chemistry atmospheric chemistry

  14. Is this model consistent with the Proterozoic? Hydrogen: Oxygen: mantle H2 source = nutrient source = hydrogen escape + aqueous & crustal oxidation + atmospheric chemistry atmospheric chemistry Across the GOE:

  15. Is this model consistent with the Proterozoic? Hydrogen: Oxygen: mantle H2 source = nutrient source = hydrogen escape + aqueous & crustal oxidation + atmospheric chemistry atmospheric chemistry Across the GOE: 1. crustal oxidation rises => atmospheric sink must decrease

  16. Is this model consistent with the Proterozoic? Hydrogen: Oxygen: mantle H2 source = nutrient source = hydrogen escape + aqueous & crustal oxidation + atmospheric chemistry atmospheric chemistry Across the GOE: 1. crustal oxidation rises => atmospheric sink must decrease 2. Slower atmos. chemistry, increasing O2 => decreasing H2

  17. Is this model consistent with the Proterozoic? Hydrogen: Oxygen: mantle H2 source = nutrient source = hydrogen escape + aqueous & crustal oxidation + atmospheric chemistry atmospheric chemistry Across the GOE: 1. crustal oxidation rises => atmospheric sink must decrease 2. Slower atmos. chemistry, increasing O2 => decreasing H2 3. Decreasing H2 => decreased H2 escape

  18. Is this model consistent with the Proterozoic? Hydrogen: Oxygen: mantle H2 source = nutrient source = hydrogen escape + aqueous & crustal oxidation + atmospheric chemistry atmospheric chemistry Across the GOE: 1. crustal oxidation rises => atmospheric sink must decrease 2. Slower atmos. chemistry, increasing O2 => decreasing H2 3. Decreasing H2 => decreased H2 escape 4. Hydrogen budget cannot be balanced in the Proterozoic!

  19. Is this model consistent with the Proterozoic? Hydrogen: Oxygen: mantle H2 source = nutrient source = hydrogen escape + aqueous & crustal oxidation + atmospheric chemistry atmospheric chemistry Across the GOE: 1. crustal oxidation rises => atmospheric sink must decrease 2. Slower atmos. chemistry, increasing O2 => decreasing H2 3. Decreasing H2 => decreased H2 escape 4. Hydrogen budget cannot be balanced in the Proterozoic! 5. …unless hydrogen escape increases, despite falling H2

  20. Oxygen-sensitive hydrogen escape • H2 escape depends on the temperature of the thermosphere. • Temperature depends on O2 absorption of UV radiation.

  21. Oxygen-sensitive hydrogen escape • H2 escape depends on the temperature of the thermosphere. • Temperature depends on O2 absorption of UV radiation. • Hydrodynamic model with Jeans boundaries • Temperature boundary related to O2 through thermosphere energy balance model (Bougher & Roble 1991)

  22. Oxygen-sensitive hydrogen escape

  23. Hydrogen escape and the Great Oxidation Archean: high H2, low O2 Oxygen controlled by reaction with free H2 Hydrogen controlled by oxidation and escape

  24. Hydrogen escape and the Great Oxidation Archean: high H2, low O2 Oxygen controlled by reaction with free H2 Hydrogen controlled by oxidation and escape Great Oxidation: large perturbation in pO2 Thermosphere warms, increasing H2 escape pH2 falls, slowing reaction with O2 Oxygen remains elevated

  25. Hydrogen escape and the Great Oxidation Archean: high H2, low O2 Oxygen controlled by reaction with free H2 Hydrogen controlled by oxidation and escape Great Oxidation: large perturbation in pO2 Thermosphere warms, increasing H2 escape pH2 falls, slowing reaction with O2 Oxygen remains elevated 3. Proterozoic: higher O2, lower H2 Oxygen controlled by weathering and respiration Hydrogen controlled by escape from a hot thermosphere

  26. Archean / Proterozoic biogeochemical model • Escape: • Hydrodynamic model with Jeans boundaries • Temperature boundary related to O2 through thermosphere energy balance model • Atmospheric chemistry: • Photochemical model of Pavlov et al. (2001) • Solid phase oxidation: • Pyrite: linear in pO2 up to 10-4 PAL • Organic carbon: linear in pO2 • Inputs: • P: 20% modern • H2: 1010 cm2 s-1

  27. Archean / Proterozoic biogeochemical model

  28. Archean / Proterozoic biogeochemical model

  29. Glaciation and oxidation Hoffman & Schrag 2002

  30. Glaciation and oxidation

  31. Glaciation and oxidation

  32. Glaciation and oxidation

  33. Glaciation and oxidation

  34. Glaciation and oxidation

  35. Glaciation and oxidation

  36. Multiple equilibria: a history of pO2

  37. Multiple equilibria: a history of pO2

  38. Multiple equilibria: a history of pO2

  39. Summary and Conclusions • The hydrogen escape rate are not diffusion limited for less-than-modern levels of pO2, but are in the Jeans regime. The escape rate varies strongly with pO2. • In our simple model, the Archean atmosphere is stabilized at low oxygen levels by the reaction kinetics between O2 and H2 in the atmosphere. Escape from the cold thermosphere is a secondary term in the H2 budget. • Hydrogen levels are suppressed at high pO2 by efficient escape from a hot thermosphere. This allows for a second equilibrium at high pO2: the weathering-dominated regime of the Proterozoic and Phanerozoic. • Transient slowing of atmospheric reactions during a >250,000 year glaciation pumps enough oxygen into the atmosphere to flip the atmosphere between its low- and high-oxygen states.

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