1 / 43

The Carbon Cycle

The Carbon Cycle. Oral review presentation, 2/7/2005 Jinbao LI (Modified from Chengyuan Xu’s presentation in 2004). What Is the Carbon Cycle ?. Carbon has two stable isotopes: 12 C (98.9%), 13 C (1.1%); one unstable isotope: 14 C

rufus
Download Presentation

The Carbon Cycle

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. The Carbon Cycle Oral review presentation, 2/7/2005 Jinbao LI (Modified from Chengyuan Xu’s presentation in 2004)

  2. What Is the Carbon Cycle? • Carbon has two stable isotopes: 12C (98.9%), 13C (1.1%); one unstable isotope: 14C • Carbon Cycle is the process by which carbon is exchanged between the biosphere, geosphere, hydrosphere and atmosphere of the Earth.

  3. Diagram of the Carbon Cycle Source: http://earthobservatory.nasa.gov/Library/CarbonCycle/carbon_cycle4.html

  4. Why Study the Carbon Cycle? • Carbon is the key element of life, thus its cycle is the most fundamental biogeochemical cycle • CO2 is the most important greenhouse gases (or called trace gases)

  5. Outline • Current change (last ~50yrs) • Historical time (<103yrs) • Glacial – Interglacial variation (103-105yrs) • Geological scale (>108yrs) (IPCC, 2000)

  6. Current CO2 Change

  7. Anthropogenic led CO2 increase • Seasonal oscillation – vegetation phenology • Increased amplitude – CO2 and N fertilization • Flattening – photosynthesis and ocean absorption http://www.cmdl.noaa.gov/ccgg/iadv/

  8. http://www.cmdl.noaa.gov/ccgg/iadv/

  9. Carbon Cycle Budget for Anthropogenic Effects

  10. Missing carbon sink: 2.8 Gt It must hide in the terrestrial biosphere Two proposed mechanisms: CO2 fertilization: fatter forests & richer soil humus N fertilization Where is the missing carbon gone?

  11. Methods to investigate the missing sink • The Mirror Image Approach • Quantifying the ocean uptake • Measure terrestrial sink

  12. Basic Reactions • Photosynthesis 6CO2+12H2*OC6H12O6+6*O2+6H2O • Respiration C6H12O6+6O26CO2+6H2O • Ocean absorption of CO2 CO2+CO32-+H2O2HCO3- CO2+H4BO4-HCO3-+H3BO3 • Weathering in soil CO2+H2OH2CO3H++HCO3-

  13. The Mirror Image Approach • 10mol CO2= 15mol O2 • 95% O2 in ATM; 5% in Ocean • Assuming no O2 exchange between Ocean-ATM • Cons: • Difficult to measure ATM O2 changes • Currently based on d(O2/ • N2)

  14. Atmosphere CO2 exchange rate (0.064mol m-2 yr-1μatm-1 ) Ocean Mixed Layer 75m Ocean Interior Eddy Diffusivity 2.4cm2s-1 The Role of the Ocean • Turnover rate about 1000 years, can totally uptake 5/6 of the excess CO2 if in equilibrium with ATM • Thickness of mixed layer (wave) • Currently, uptake about 50% missing carbon (2-3Gt) • Eddy diffusivity (bomb 3H and 14C penetration in ocean) • The extent of vertical mixing varies as the square root of time

  15. Modeling Ocean Uptake of CO2 • Key: Ocean-ATM CO2 exchange rate • Methods: • Use natural and bomb 14C, Radon, fossil fuel 13C as tracer gases

  16. Other Scenarios • Use gas exchange rate and air-ocean pCO2 gradient to estimate CO2 uptake – too large error bar (4± 4 ppm difference, 8ppm equals 2Gt uptake)

  17. Interhemisphere CO2 gradient • Increased gradient since 1950 • Higher CO2 in South hemisphere before 1950 • Excess CO2 carried by NADW to Antarctic (0.6Gt) • Due to the difference of nutrients contents (PO4) • 0.8umoles/l in North Atantic; 1.6umoles/l in Antatctic Ocean

  18. Terrestrial Carbon Sink • Photosynthesis reaction to CO2 • In general, 10% growth increase if [CO2] content 30% higher • Nitrogen fertilization

  19. Leaf 2yrs Model 150Gt 0.2Gt/yr Wood 60yrs 500Gt 0.3Gt/yr • 1.1 Gt in all for CO2 fertilization mainly in North America and Euroasia • 0.5 Gt for Nitrogen fertilization Active Soil 15 yrs 75% 500Gt 0.5Gt/yr Inert Soil 3500 yrs Additionally, 0.04Gt N fertilization/yr and C/N=12

  20. Historical Change

  21. Historical Change Pre-industrial:280ppm Current: ~380ppm http://www.acad.carleton.edu/curricular/GEOL/DaveSTELLA/Carbon/carbon_intro.htm

  22. Glacial-Interglacial Change

  23. Glacial-Interglacial CO2 variation • Vostok ice core in Antarctic showed 80ppm CO2 rise (200 to 280) when glacial era ends (till 400,000 years ago) • Ice core in Dansgarard-Oeschgar is Greenland was contaminated by acid released CO2 from CaCO3

  24. CO2 inventory during glacial era • Interglacial  Glacial: Atmosphere CO2 decrease 80 ppm • Glacial cooling: 20C cooling in North Atlantic decrease atmosphere CO2 by 20 ppm • Salinity: increase 3%, raising CO2 for 10 ppm • Reduction of terrestrial biosphere: equaling inject 56 ppm CO2 to atmosphere, among which 40 ppm is absorbed by ocean • In all, we still need to explain about 80 ppm CO2 decline

  25. Biological Pump • Nutrient limits productivity in ocean • Fe:P:N:C =1:1000:16000:125000 http://www.awi-bremerhaven.de/GEO/Publ/PhDs/RUsbeck/node5.html

  26. In regions of strong upwelling much of nutrients goes unused • If fully used, ATM CO2 drops to glacial level

  27. Iron Fertilization • Higher dust input to ocean during glacial • High Fe facilitated cynaobacteria in the tropic, which fix N • Several thousand years lag between dust decline and temperature increase

  28. Ocean Inorganic Carbon Pool and Lysocline • In ocean, [CO2] ≈ 1/[CO32-] • So dissolution of CaCO3 can decreased pCO2 • Lysocline marks the depth below which CaCO3 will dissolve • Lysocline is supposed to decline for 3000 meters if CO2 decrease 80 ppm, but we observed on 800m • Respiration of bacteria at ocean bottom can also dissolve CaCO3 and may decouple the relationship • Supported by paleo pH proxy (B(OH)3/B(OH)4-), pH increased 0.3 and [CO32-] doubled • Biological pump can increase organic C deposition and breed bacteria

  29. Other Scenarios • Coral reef growth releases CO2 into the atmosphere. • Coral Reef generation decreased during glacial time due to the decline of sea level and more coral exposed to air subjecting to erosion • Lower marine organism calcite production, perhaps due to the competition advance of diatom • Due to more freeze-thaw activity, more alkalinity input into ocean which increase [CO32-]

  30. Geological Time Scale

  31. Faint Young Sun Paradox • The Sun burns H to produce He (4H---> He); • Its energy was 30% lower 4.6 Bys ago (25% lower 3.8Bys) • Liquid water existed on earth for 3.8 Bys (sediment), indicating constant earth temperature • Some temperature regulator • Solution: Higher ATM CO2

  32. High ATM CO2: Warming or Cooling? • Venus • So much CO2 accumulate in the atmosphere that water evaporated before feedback works • No sediment can form and the regulation ends • 430°C at surface • Snowball Earth • If so few CO2 stay in atmosphere, the ATM temperature drop below to –80°C • Before melting the ice cover all CO2 outgassing become dry ice • Cool the earth

  33. our planet was thought to have been completely covered with ice at least twice during the late Proterozoic era (one 740 and another 550 million years ago). • Ice sheets may have reached the Equator • Glacial tills overlain by ‘cap carbonates’, indicating the events ended by CO2 warming • The deglaciation was associated with exceptionally severe wind and wave conditions, thus the snowball may go down a storm. Snowball Earth Hypothesis

  34. Global Carbon Cycle at Geological Scale Organic C

  35. BLAG Scenario • The rate of CO2 release from the Earth’s interior is proportional to the rate of sea-floor spreading. • The main factor perturbing the Earth’s CO2 budget over the last 100myrs was gradual slowdown of the sea-floor spreading rate.

  36. To Test the Scenario • Outgassing CO2 should equal CaCO3 subducted • Calcium input from terrestrial silicates should balance air CO2 deposited • The sea floor spread was much faster 1 Mys ago (Pittman and Hays), so there should be more CO2 outgassing. More CaCO3 sediments and weathering was expected to maintain the balance of carbon. • Warmer 1 Mys ago • Higher atmosphere CO2 concentration 1 Mys ago

  37. Another Test of BLAG • Polar climate cooled since 60 mys ago • Based on BLAG, CO2 release decreased, so is land chemical weathering

  38. Estimating Weathering rate • Use 87Sr/87Sr (Strontium) in foraminifera, which reflects ocean 87Sr/87Sr • Terrestrial derived Sr is more 87Sr enriched than hydrothermal ridge derived Sr • Unfortunately, the elevated 87Sr/87Sr since 40 Mys ago was caused by the rise of Himalaya, which brings 87Sr enriched Sr to continent

  39. (BLAG) Policeman in the ATM Ca supplied to the ocean is entirely removed as CaCO3 CaO is closely tied to CO2 BLAG vs GALB (GALB) • Policeman in the Ocean • Silicate minerals is an major additional sink for Ca • CaO is controlled by the pH of deep sea water

  40. Long Term CO2 Record Spread of vascular plants 550myrs “Snow Ball Earth” Event 440myrs First land plant 400myrs First tree like plant 360myrs First Soil Large glacial event

  41. Other Stuff to Remember • P-T (Permo-Triassic) Boundary • 250 million years ago • The greatest mass extinction in the history of marine life • Extinction hypotheses: intense volcanic activity

  42. Other Stuff to Remember • K-T (Cretaceous-Tertiary) Boundary • 65 million years ago • A large fraction of plant and animal families suddenly went extinct • Possibly caused by the impacts of Asteroids

  43. The End

More Related