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Ocean Carbon Cycle

Ocean Carbon Cycle. Figure credit US-OCB Program. Why study ocean carbon cycle?. CO 2 is an important greenhouse gas Ocean is a major sink of fossil fuel CO 2 Impacts on ocean chemistry. Rising atmospheric CO 2. SIO CO 2 program. Polar ice core data. Instrumental record.

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Ocean Carbon Cycle

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  1. Ocean Carbon Cycle Figure credit US-OCB Program

  2. Why study ocean carbon cycle? • CO2 is an important greenhouse gas • Ocean is a major sink of fossil fuel CO2 • Impacts on ocean chemistry

  3. Rising atmospheric CO2 SIO CO2 program Polar ice core data Instrumental record

  4. Global average ~ 1.2 TC/year/person

  5. Units for atmospheric CO2 • What do we mean by 390 ppmv? • About 0.039% of all gas molecules in the atmosphere is CO2 • CO2is a minor component of the atmospheric gases

  6. Current atmospheric CO2 is about 390 ppmv, which is equivalent of 780 GTC. Simple rule of thumb

  7. Unit matters • 1 molC = 12 gC = 44 gCO2 • 1 gC = 3.7 gCO2 • molC and gC are most frequently used in scientific literature • gCO2is also used in media, etc. • Watch out for different units!

  8. Global carbon inventory estimates • Atmosphere : 780 GTC • CO2 gas • Land biosphere : 2,000 GTC • Organic matter in forestand soils • Oceans : 38,000 GTC • Dissolved Inorganic Carbon (DIC) = CO2 gas dissolved in the seawater • Geological reservoirs • Seafloor sediment : 150 GTC • Oilreservoir : 500 GTC • Coal reservoir : 5,000 GTC

  9. Order of magnitude • 1 metric ton of C (TC) = 106gC • In 2009, US per capita carbon emission is 4.6 TC • Global CO2 emission in 2008 is about 9 GTC • 1 giga ton of C (GTC) • 1GTC = 109TC = 1015gC = 1 PgC • 1PgC = 1015gC x (1molC/12gC) = 8.3 x 1013molC 100 103 106 109 1012 1015 G k T M P kilo mega giga tera peta

  10. Concept test • Company A sells a product that reduces carbon emission at a cost of $10/TCO2 • Company B sells similar product ata cost of $20/TC • Which company is offering more cost-effective product?

  11. Concept test • If we consume entire oil reservoir, 500 GTC, how many ppmv increase do we expect in the atmosphere? • (case 1) No absorption into the ocean and/or land • (case 2) 50% absorption • (case 3) 75% absorption

  12. Emission due to human activities • DOE: Carbon Dioxide Information Analysis Center

  13. Oceans Biosphere CO2 changes in the last 50 yr

  14. The Carbon sinks • CO2 emission due to human activity • About 9 GTC/year • Time rate of increase in atmospheric CO2 • Late 2000s • Observed increase is about 4 GTC/year • Only about 45% of CO2 emitted by the human activity is remaining in the atmosphere • Where has the rest of CO2 gone?

  15. Land and ocean carbon sinks • Land biosphere • Carbon molecule is stored in trees, plants and soils • Ocean CO2 uptake • Absorption of CO2into the seawater • The carbon cycle has a stabilizing mechanism, mediating the growth of atmospheric CO2 by absorption into the land and oceans

  16. Photosynthesis and respiration • Solar energy + CO2 + H2O  Sugar + O2 • Most of energy stored in sugar is released by respiration when the biomass is consumed by animals, bacteria and people • If there is a net surplus in biomass production, biosphere can become a carbon sink

  17. Carbon uptake by the land biosphere • (Land uptake) = (Photosynthesis) – (Respiration) • Photosynthesis • Water, nutrients, sunlight • Respiration • Decomposition of organic matter • Organic matter  CO2 • Episodic events: ex. forest fires

  18. Air-sea gas transfer • Driven by turbulence at the air-sea interface • What controls the turbulent motion? Emerson and Hedges (2010)

  19. Gas transfer coefficient: G [ms-1] • Measures the strength of the air-sea gas transfer

  20. Modeling air-sea gas transfer • Sea-to-air gas flux [mol m-2 s-1] • Measures exchange of gas molecules per unit area and per unit time • Proportional to the degree of saturation Henry’s law coefficient

  21. Chemical reactions with the seawater • A series of reactions CO2 + H2O H2CO3 (carbonic acid) H2CO3 H+ + HCO3- (bicarbonate ion) HCO3-H+ + CO32- (carbonate ion) Textbook chapter 6, page 180-183

  22. Carbonate chemistry • DIC = (Dissolved Inorganic Carbon) = [CO2] + [H2CO3]+ [HCO3-]+ [CO32-] • DIC is a conserved quantity with respect to the carbonate chemistry

  23. Buffer (Revelle) factor • Fractional changes in pCO2 is related to that of DIC with a constant factor, B. • Buffer (Revelle) factor is about 10 for the modern oceans • 10% increase in pCO2 leads to 1% increase in DIC

  24. Concept test • Since industrial revolution, atmospheric pCO2 has increased from 280 to 390 ppmv. • How accurate do we need to measure DIC in order to detect the influence of rising CO2on the surface ocean DIC concentration?

  25. A little more challenging test • Let’s assume that we consume entire oil reservoir, 500 GTC, and half of coal reservoir, 2500 GTC. • If this carbon remains in the atmosphere, what would be the resulting pCO2? • What happens if we allow the entire ocean carbon reservior to respond to the rising CO2?

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