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

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Presentation on theme: "Multiple Equilibria in Atmospheric Oxygen: Archean, Proterozoic, Phanerozoic. Tom Laakso & Dan Schrag Goldschmidt Geochemistry June 13, 2014."— Presentation transcript:

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

2 Kump 2008 Multiple Equilibria in pO 2

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 Kump 2008 The Great Oxidation Event

6 hydrogen outgassing serpentinization Archean redox budget: prebiotic world

7 mantle hydrogen source Archean redox budget: prebiotic world

8 mantle hydrogen source hydrogen escape Archean redox budget: prebiotic world

9 mantle hydrogen source hydrogen escape chemoautotrophy: 2 H 2 + CO 2 H 2 O + CH 2 O Archean redox budget: early life

10 mantle hydrogen source hydrogen escape organic burial (< nutrient input) chemoautotrophy: 2 H 2 + CO 2 H 2 O + CH 2 O Archean redox budget: early life

11 mantle hydrogen source hydrogen escape organic burial (< nutrient input) chemoautotrophy: 2 H 2 + CO 2 H 2 O + CH 2 O oxygenic photosynthesis CH 2 O + O 2 CO 2 + H 2 O Archean redox budget: oxygenic photosynthesis

12 mantle hydrogen source hydrogen escape organic burial (< nutrient input) chemoautotrophy: 2 H 2 + CO 2 H 2 O + CH 2 O oxygenic photosynthesis CH 2 O + O 2 CO 2 + H 2 O oxidation: seafloor, aqueous, continental oxidation: atmosphere Archean redox budget: oxygenic photosynthesis

13 Hydrogen: Oxygen: mantle H 2 source = nutrient source = hydrogen escape + aqueous & crustal oxidation + atmospheric chemistry atmospheric chemistry Archean equilibrium redox budget

14 Hydrogen: Oxygen: mantle H 2 source = nutrient source = hydrogen escape + aqueous & crustal oxidation + atmospheric chemistry atmospheric chemistry Across the GOE: Is this model consistent with the Proterozoic?

15 Hydrogen: Oxygen: mantle H 2 source = nutrient source = hydrogen escape + aqueous & crustal oxidation + atmospheric chemistry atmospheric chemistry Across the GOE: 1. crustal oxidation rises => atmospheric sink must decrease Is this model consistent with the Proterozoic?

16 Hydrogen: Oxygen: mantle H 2 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 O 2 => decreasing H 2 Is this model consistent with the Proterozoic?

17 Hydrogen: Oxygen: mantle H 2 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 O 2 => decreasing H 2 3. Decreasing H 2 => decreased H 2 escape Is this model consistent with the Proterozoic?

18 Hydrogen: Oxygen: mantle H 2 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 O 2 => decreasing H 2 3. Decreasing H 2 => decreased H 2 escape 4. Hydrogen budget cannot be balanced in the Proterozoic! Is this model consistent with the Proterozoic?

19 Hydrogen: Oxygen: mantle H 2 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 O 2 => decreasing H 2 3. Decreasing H 2 => decreased H 2 escape 4. Hydrogen budget cannot be balanced in the Proterozoic! 5. …unless hydrogen escape increases, despite falling H 2 Is this model consistent with the Proterozoic?

20 Oxygen-sensitive hydrogen escape H 2 escape depends on the temperature of the thermosphere. Temperature depends on O 2 absorption of UV radiation.

21 Oxygen-sensitive hydrogen escape H 2 escape depends on the temperature of the thermosphere. Temperature depends on O 2 absorption of UV radiation. Hydrodynamic model with Jeans boundaries Temperature boundary related to O 2 through thermosphere energy balance model (Bougher & Roble 1991)

22 Oxygen-sensitive hydrogen escape

23 Hydrogen escape and the Great Oxidation 1.Archean: high H 2, low O 2 Oxygen controlled by reaction with free H 2 Hydrogen controlled by oxidation and escape

24 Hydrogen escape and the Great Oxidation 1.Archean: high H 2, low O 2 Oxygen controlled by reaction with free H 2 Hydrogen controlled by oxidation and escape 2.Great Oxidation: large perturbation in pO 2 Thermosphere warms, increasing H 2 escape pH 2 falls, slowing reaction with O 2 Oxygen remains elevated

25 Hydrogen escape and the Great Oxidation 1.Archean: high H 2, low O 2 Oxygen controlled by reaction with free H 2 Hydrogen controlled by oxidation and escape 2.Great Oxidation: large perturbation in pO 2 Thermosphere warms, increasing H 2 escape pH 2 falls, slowing reaction with O 2 Oxygen remains elevated 3. Proterozoic: higher O 2, lower H 2 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 O 2 through thermosphere energy balance model Atmospheric chemistry: Photochemical model of Pavlov et al. (2001) Solid phase oxidation: Pyrite: linear in pO 2 up to PAL Organic carbon: linear in pO 2 Inputs: P: 20% modern H 2 : cm 2 s -1

27 Archean / Proterozoic biogeochemical model

28 Archean / Proterozoic biogeochemical model

29 Glaciation and oxidation Hoffman & Schrag 2002

30 Glaciation and oxidation

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36 Multiple equilibria: a history of pO 2

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39 Summary and Conclusions The hydrogen escape rate are not diffusion limited for less-than-modern levels of pO 2, but are in the Jeans regime. The escape rate varies strongly with pO 2. In our simple model, the Archean atmosphere is stabilized at low oxygen levels by the reaction kinetics between O 2 and H 2 in the atmosphere. Escape from the cold thermosphere is a secondary term in the H 2 budget. Hydrogen levels are suppressed at high pO 2 by efficient escape from a hot thermosphere. This allows for a second equilibrium at high pO 2 : 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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