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Unformatted text preview: IV. The Long-Term Organic Carbon Cycle Carbon
a. On longer time scales, the processes must On be closely in balance be
i. Fluxes involved are very large ii. Persistent imbalances would lead to intolerable Persistent fluctuations in atmosphere CO2 fluctuations b. Geological processes become important Geological controls of atmospheric CO2 controls
i. ii. Carbon fluxes are small Reservoirs are large IV. The Long-Term Organic Carbon Cycle IV.
c. Carbon burial in sedimentary rocks
i. Organic carbon is captured in rock until Organic weathering liberates the material to the biosphere biosphere ii. Carbon leaks and oxygen replenishment
1. Organic carbon burial is a leak from the short-term Organic cycle cycle 2. Maintains O2 in atmosphere
a. O2 removed from atmosphere 1. Chemical reactions with reduced materials (rust; Chemical oxidation) oxidation) 2. Volcanic gases H b. O2 is replenished by the leak of matter into the rock reservoir IV. The Long-Term Organic Carbon Cycle Carbon
c. Carbon burial in sedimentary rocks iii. Formation of fossil fuels 1. significant changes in structure and 1. chemistry of organic material chemistry 2. high temperature and pressures lead to 2. the formation of coal the 3. Marine sediments under similar 3. conditions can produce petroleum conditions 4. Material is fluid and flows until it is 4. trapped and accumulates trapped IV. The Long-Term Organic Carbon Cycle IV.
d. Weathering of organic carbon in sedimentary d. rocks rocks
i. An oxidation process requiring atmosphere O2
1. Direct exposure to atmosphere 2. Exposure to groundwater with O2 ii. Organic matter reacts with O2, releases CO2 iii. Mining, pumping, or combustion of fossil fuels Mining, accelerates weathering accelerates iv. Release of organic matter from rock is occurring Release much faster than it can be replenished much Short-term & Long-term organic carbon cycles carbon IV. The Long-Term Organic Carbon Cycle Carbon
e. Summary of the organic carbon cycle ii. Pathways exist to recycle carbon from . all reservoirs all iii. Every reservoir is connected to the i. atmosphere atmosphere iiii. The CO2 concentration of the ii. atmosphere changes continuously in response to changes in the flux of carbon carbon V. The Inorganic Carbon Cycle V.
a. Other sources and sinks for atmospheric a. CO2 CO
i. Dissolves in rain or sea water iii. Chemical reactions convert it to i. inorganic carbon inorganic iiii. Oxidized carbon becomes chemically ii. reactive reactive b. Important reservoirs include b. atmosphere, ocean, sediments and sedimentary rocks Global Inorganic Carbon Cycle V. The Inorganic Carbon Cycle V.
c. Carbon exchange between the ocean and atmosphere i. Continual exchange of CO2 ii. Distribution of sources and sinks is tied to circulation and productivity pattern 1. Regions with high primary productivity a. Surface water with low CO2 b. 2. CO2 diffuses from atmosphere to ocean Upwelling regions a. Surface waters have high CO2 and nutrient content b. iii.
1. 2. CO2 flow from ocean to atmosphere Before the carbon cycle was disturbed by humans
-the CO2 flux from oceanic sources was balanced by sinks Weak sources have now become sinks Whole ocean has become a sink for CO2 Sources and Sinks V. The Inorganic Carbon Cycle V.
d. The chemistry of inorganic carbon in water
i. i. Production of Carbon Acid CO2 + H 2O ↔ H 2CO3 Carbonic acid molecules break apart into ions
1. 2. 3. Anions- (-) charge Cations- (+) charge Concentration of carbon anions linked to pH of seawater V. The Inorganic Carbon Cycle V.
d. The chemistry of inorganic carbon in water i. Production of Carbon Acid CO2 + H 2O ↔ H 2CO3
(1) Carbon dioxide and water produce carbonic acid V. The Inorganic Carbon Cycle V.
d. The chemistry of inorganic carbon in water ii. Carbonic Acid, Bicarbonate, and Carbonate Ion Equilibrium H 2CO3 ↔ H + + HCO3− HCO3− ↔ H + + CO32− 1. Loss of H atom produces bicarbonate ion
a. b. c. Decreasing H+ concentration lowers pH More carbonic acid would dissociate to balance and bring equilibrium Carbonic acid is formed at the expense of bicarbonate ion acidic water 2. 3. 4. 5. Loss of a second H atom The relative amounts of bicarbonate and carbonate ions adjust to equilibrium As pH lowers decreases from alkaline to acidic , the ratio of carbonate to bicarbonate ion decreases Perturbation of equilibrium changes the pH
a. b. Anthropogenic CO2 Changes in pH impact relative concentrations i. CO2 dissolves carbonic acid, Carbonic dissolves acid to form bicarbonate, pH drops, H+ ions react with carbonate to form another bicarbonate V. The Inorganic Carbon Cycle V. V. The Inorganic Carbon Cycle V. Loss of an H atom produces a bicarbonate ion Loss of a second H atom converts bicarbonate ion to carbonate ion H 2CO3 ↔ H + HCO HCO ↔ H + CO
− 3 + 2− 3 + − (2) Carbonic acid dissociates to produce 3 bicarbonate ion
(3) Bicarbonate ion converted to carbonate ion V. The Inorganic Carbon Cycle V. The uptake of anthropogenic CO2 is the sum of 1, 2, and the reverse of 3 CO2 + H 2O ↔ H 2CO3 H 2CO3 ↔ H + HCO HCO ↔ H + CO
2− 3 − 3 + 2− 3 − 3 + − 3 CO2 + CO + H 2O ↔ 2 HCO Carbon dioxide, carbonate ion, water leads to 2 bicarbonate ions V. The Inorganic Carbon Cycle V.
e. Chemical Weathering
CaCO3 + H 2CO3 → Ca + + 2 HCO3− Weathering of calcium bearing minerals CaSiO3 + 2 H 2CO3 → Ca 2+ + 2 HCO3− + SiO2 + H 2O Ca ions are used by organisms to create shells and skeletons Carbonates- contain Ca, C, and O
a. b. Calcite, Dolomite Limestone, Dolostone ii. i. Exposed to rain both carbonate and silicates weather
1. Chemical weathering neutralizes the acidity of carbonic acid Silicate weathering consumes 2 times as much carbonic acid ...
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This note was uploaded on 04/11/2011 for the course EAS 253 taught by Professor Dr.emilyberndt during the Spring '11 term at Saint Louis.
- Spring '11