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The C-cycle

The C-cycle. a re-cycling system Biosphere subcycle —terrestrial and marine realms, inorganic and organic pathways, fast cycling Lithosphere subcycle —long term storage and tectonic re-cycling, slow cycling . Definitions. Nutrients —substances essential to life

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The C-cycle

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  1. The C-cycle • a re-cycling system • Biosphere subcycle—terrestrial and marine realms, inorganic and organic pathways, fast cycling • Lithosphere subcycle—long term storage and tectonic re-cycling, slow cycling

  2. Definitions • Nutrients—substances essential to life • Biosphere—the part of the Earth that supports life, including the oceans, atmosphere, land surface and soils • Organic carbon—associated with compounds of biologic systems (C-C and C-H bonds) • Inorganic carbon—associated with compounds of inorganic systems

  3. Elements of the C-cycle 10 y 50 y Decay in soils (oxidation)

  4. Elements of the C-cycle 10 y 50 y Decay in soils (oxidation) One atom of C cycles for about 30 Ky before leaking into sedimentary storage

  5. Elements of the C-cycle 10 y volcanism re-cycles C weathering re-cycles C 50 y Decay in soils (oxidation) uplift metamorphism subduction nMy

  6. Carbon Reservoir Dynamics • Carbon reservoirs • How does the size of each carbon reservoir respond to perturbations

  7. Carbon Reservoir Dynamicsatmospheric reservoir Seasonal fluctuation in atmospheric CO2 from Mauna Loa

  8. Carbon Reservoir Dynamicsatmospheric reservoir • Reservoirs are temporary repositories for mass that flows through them, their sizes depending on imbalances between inflow and outflow • Steady-state—no change in state of the system with time

  9. Carbon Reservoir Dynamicsperturbation of the atmospheric reservoir CO2 fertilization negative feedback loop  atm CO2 — photosynthetic rate (reduced organic carbon)— atm CO2

  10. Residence time • The average time that an element remains in a reservoir at steady-state • The time required to fill a reservoir to the steady-state concentration

  11. Carbon Reservoir Dynamicsresidence time of C in the atmosphere 760 Gton carbon / 60 Gton carbon/yr = 12.7 yr

  12. Organic C-cycle (short term) • Photosynthesis CO2 + H2O = CH2O + O2 • Primary producers • Consumers • Biomass = primary producers + consumers • Consumers are 1% of biomass

  13. Primary producers in the seaphytoplankton (upper 100m in photic zone) Coccolithoforid with calcite test (10mm diameter) Diatom with sliceous test (50mm diameter)

  14. Planktonic consumers in the seazooplankton Radiolarian with siliceous test (50mm diameter) Foraminifera with calcite test (600mm diameter)

  15. The biological pump • Primary production of organic C in surface waters — oxidation of organic C in deeper waters • Settling organic particles by-pass fluid advection • Balanced by upwelling

  16. The biological pump

  17. Nutrient limitation Concentration of some elements in seawater limit productivity (P, Si, Fe)

  18. Nutrient limitation

  19. Nutrient and oxygen distribution in the abyss

  20. Thermohaline circulation

  21. Nutrient limitation Vertical distribution of Fe

  22. Ocean productivity measured by satellite (chlorophyll) Summer Winter

  23. Upwelling and nutrient recycling

  24. Organic C-cycle (long term) • Geological processes control atmospheric CO2 on longer time scales • 0.1% of marine productivity leaks into long term geologic storage • This leak controls the O2 content of the atmosphere CO2 + H2O =  CH2O +  O2 • organic C in sedimentary rocks is the largest reservoir on earth (108 Gtons) • Residence time is 200 Ma

  25. Inorganic C-cycle • Describes sources and sinks of carbon other than respiration decomposition and weathering • CO2 reacts with water CO2 (g)+ H2O(l) = H2CO3(aq) H2CO3(aq) = H+ + HCO3– HCO3–= H+ + CO3–2 • Limestone (CaCO3) and dolostone (CaMg(CO3)2 are long term sedimentary archives of inorganic carbon Ca+2 + 2HCO3(aq)– = CaCO3 (s)+ H2CO3(aq)

  26. Seawater-atmosphere exchange of CO2

  27. Carbonate deposition in the oceans

  28. Chemical weathering of Ca-bearing minerals • Carbonate weathering CaCO3 (s)+ H2CO3(aq) = Ca+2 + 2HCO3(aq)– • Silicate weathering CaSiO3 (s)+ 2H2CO3(aq) = Ca+2 + 2HCO3(aq)– +SiO2 (aq) +H2O • Carbonate weathering on land consumes 1 mole of CO2 per mole of Ca released—the net effect on CO2(atm) is zero • Silicate weathering on land consumes twice the amount of CO2 as Ca—the net effect on CO2(atm) is a reduction of 1 mole equivalent

  29. Carbonate-silicate cyclelong term climate stability Carbonate metamorphism (reverse of silicate weathering) CaCO3 (s)+ SiO2 (s) = CaSiO3 (s)(wollastonite) + CO2 (g)

  30. Net result of silicate weathering CaSiO3 (s)+ 2H2CO3(aq) = Ca+2 + 2HCO3(aq)– +SiO2 (aq) +H2O Ca+2 + 2HCO3(aq)– = CaCO3 (s)+ H2CO3(aq) CO2 (g)+ H2O(l) = H2CO3(aq) CaSiO3 (s)+ CO2 (g) = CaCO3 (s) + SiO2 (aq)

  31. Net result of silicate weathering CaSiO3 (s)+ 2H2CO3(aq) = Ca+2 + 2HCO3(aq)– +SiO2 (aq) +H2O Ca+2 + 2HCO3(aq)– = CaCO3 (s)+ H2CO3(aq) CO2 (g)+ H2O(l) = H2CO3(aq) CaSiO3 (s)+ CO2 (g) = CaCO3 (s) + SiO2 (aq)

  32. Carbonate-silicate cyclelong term feedbacks ensure stability of the Earth’s climate system

  33. Carbonate-silicate cyclelong term feedbacks ensure stability of the Earth’s climate system C-leak Limestone deposition C-leak volcanism limestone metamorphism

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