The Biogeochemical Carbon Cycle: CO 2 ,the greenhouse effect, & climate feedbacks

1. The Biogeochemical Carbon Cycle: CO2,the greenhouse effect, & climate feedbacks Assigned Reading: Kump et al. (1999) The Earth System, Chap. 7.

2. Overhead Transparencies

3. Faint Young Sun Paradox 41H→4He Incr.density = Incr.luninosity Liquid H2O existed >3.5 Ga (sed. Rocks, life, zircon 18O)

4. Simple Planetary Energy Balance •Likely solution to FYSP requires understanding of Earth’s energy balance (& C cycle)

5. Energy Absorbed

6. Neither Albedo or Geothermal Heat Flux Changes Can Keep the Earth from freezing w/ 30% lower S

7. Lower S compensated by larger greenhouse effect

8. The Electromagnetic Spectrum

9. Incoming UV, Outgoing IR “Greenhouse Gases” absorb IR radiation efficiently

10. Molecules Acquire Energy when they Absorb Photons

11. 1.CO2 Feedbacks: Geochemical Carbon cycle ‧Transfer of C between rocks and ocean/atmosphere (> 106-yr) can perturb CO2 greenhouse effect ‧Ocean/atmosphere C reservoir small w.r.t. rock reservoir and the transfer rates between them Carbon Cycle: Strong driver of climate on Geologic timescales 2.Evidence for Long-Term CO2-Climate Link 3.Case Studies: Permo-Carboniferous Glaciations Warm Mesozoic Period Late Cenozoic Cooling

12. The Geochemical Carbon Cycle The Bio- Geochemical carbon Cycle 1. Organic Carbon Burial and Weathering 2. Tectonics: Seafloof spreading Rate Mantle CO2 from Mid-Ocean Ridges 3. Carbonate-Silicate Geochemical Cycle Chemical Weathering Consumes CO2 Carbonate Metamorphism Produces CO2

13. Chemical Weathering = chemical attack of rocks by dilute acid Geochemical Carbon Cycle #2 • Carbonate Weathering: 2. Silicate Weathering: consumption for silicates Carbonates weather faster than silicates

14. Carbonate Rocks Weather faster than Silicate rocks!

15. Net Reaction of Rock Weathering Carbonate and Silica Precipitation in Ocean Net reaction of geochemical carbon cycle (Urey Reaction) consumed Would deplete atmospheric Plate tectonics returns via Volcanism and Metamorphism Carbonate Metamorphism produced from subducted marine sediments

16. Geologic record indicates climate has rarely reached or maintained extreme Greenhouse or Icehouse conditions....Negative feedbacks between climate andGeochemical Carbon Cycle must existThus far, only identified for Carbonate-Silicate Geochemical Cycle: Temp., rainfall enhance weathering rates (Walker et al, 1981) (I.e., no obvious climate dependence of tectonics or organic carbon geochemical cycle.) How are CO2 levels Kept in Balance? Feedbacks • Adapted from Kump • et al. (1999)

17. A Closer Look at the Biogeochemical Carbon & the Organic Carbon Sub-Cycle

18. BIOGEOCHEMICAL CARBON CYCLE ATMOSPHERE CO2 Exhalation CO2 rock weathering sink dissolution sink fixation OCEANS CONTINENTAL EROSION IGNEOUS ROCKS Uplift BIOSPHERE SEDIMENTS METAMORPHIC ROCKS lithification SEDIMENTARY ROCKS Organic matter Corg

19. Earth's Carbon Budget Biosphere, Oceans and Atmosphere Crust Mantle

20. Steady State & Residence Time Steady State: Inflows = Outflows Any imbalance in I or O leads to changes in reservoir size Inflow: Outflow: Atmospheric Respiration Photosynthesis The Residence timeof a molecule is the average amount of time it is expected to remain in a given reservoir. of atmospheric Example

21. Carbon Reservoirs, Fluxes and Residence Times Species Amount Residence Time Sedimentary carbonate-C Sedimentary organic-C Oceanic inorganic-C Necrotic-C Atmospheric-CO2 Living terrestrial biomass Living marine biomass

22. Carbonate-Silicate Geochemical Cycle • CO2 released from volcanism dissolves in H2O, forming carbonic acid H2CO3 • CA dissolves rocks • Weathering products transported to ocean by rivers • CaCO3 precipitation in shallow & deep water • Cycle closed when CaCO3 metamorphosed in

23. Simple Carbon Cycle Modeling Total C entering atm. & oceans = Total C buried in sediments closed system 13C into atm. & oceans =13C being buried in sediments conservation of isotopes ~5 the avg. value for crustal C isotopic fifference between inorganic and organic carbon Hayes et al., Chem Geol. 161.37.1999; Des Mariais et al., Nature 359.605.1992

24. Carbon Isotopic Excursions 808-500Ma More complete sediment record + Improved chronology = More detailed picture showing Abrupt and extreme C-isotopic shifts A global composite of 13C data shows 4 excursions Plus one at the pC-C boundary

25. Carbon Isotopic Excursions 808-500Ma More complete sediment record + Improved chronology = More detailed picture showing Abrupt and extreme C-isotopic shifts

26. Modeling the Proterozoic Carbon Cycle • carb and org through time 2500-550 Ma in 100Ma increments • note the constancy of carbwhile org decreased. Why? biochemistry • or pCO2 • forg increased through this time, was episodic and was linked to periods of rifting and orogeny •  also associated with extreme glaciations • Increase in the crustal inventory of C requires increases in the inventories of crustal Fe3+ , crustal and marine sulfate, nitrate and atmospheric oxygen. •  SO4 , NO3- and O2 increases changed patterns of respiration •  NO3- would have forced productivity changes