ARCHER FIG. 8.1 5/5/2015 Fraction of Earth’s C 50x C of atmSeveral times more C than atm Lots of C!! Mostly limestone sedimentary rocks
1. C exists in a range of forms Most stable as CO 2 and CaCO 3 2. Photosynthesis stores energy by producing organic carbon 3. Atmosphere contains only a fraction of carbon 4. Biosphere has several more times carbon than atm Seasonal signal seen 5, Oceans contains 50x C of atmosphere Responsible for large changes in CO 2 over 100,000 year time scales 6. Weathering of rock consumes CO 2 on timescales of millions of years
CARBON SINKS (RESERVOIRS) Reservoir that uptakes a chemical element from another part of its cycle. Each year hundreds of billions of tons of carbon, in the form of CO 2, are absorbed by oceans, soils, plants.
SINKS (1) biosphere - living and dead material +organic matter in soils (2) atmosphere – CO 2 (3) lithosphere - fossil fuels, sedimentary rocks (4) Oceans - dissolved CO 2 & calcium carbonate (shells) in marine organisms. 5/5/2015
CARBON FLUXES Plants - CO 2 from atmosphere. CO 2 enters ocean by diffusion. Used to produce shells (coral, clams) Organisms die, shells sink to the ocean floor. After long periods of time, deposits are physically and chemically altered into sedimentary rocks.
CARBON FLUXES Carbon from ecosystems as CO 2 by respiration. Respiration - both plants and animals -breakdown of carbon-based organic molecules into CO 2 detritus food chain - decomposition of organic matter. Natural ecosystems store between 20 to 100x more CO 2 than agricultural land.
CARBON ON EARTH --- START HERE WEEK 9 Now let’s back up to the beg. of the chapter and think about Carbon in more detail… p. 89 Backbone for constructing the machinery of life & provides the means of storing energy. Photosynthesis – converts suns energy into carbon biomolecules. Energy then used by plant, or animal that eats it. 5/5/2015
CARBON ON EARTH Over geologic timescales, carbon stores energy on a planetary scale. “Charges up” the biosphere with a store of biomolecules like a giant battery. Extracting energy from fossil fuels harvests ancient energy stores of the biosphere. Rearranges the distribution of carbon among its reservoirs (sinks) on Earth. 5/5/2015
CARBON ‘Rich, wondrous chemistry’ Carbon chemistry is kept highly organized within living things. Then, after life is finished carbon left in soils, sediments, and rocks forms itself into humic acids or kerogen. The number of configurations of carbon is infinite. 5/5/2015
HUMIC ACIDS/HUMIC SUBSTANCES Major constituents of soil organic matter Precursors of fossil fuels found in peat, coal, streams/lakes, ocean Created by microbial degradation of dead plant and animal material. Most stable part of organic matter in soils, can persist for tens, hundreds or even thousands of years. 5/5/2015
KEROGEN Mixture of organic chemical compounds that make up a portion of the organic matter in sedimentary rocks. crude oil or natural gas, hydrocarbons oil shale deposits 5/5/2015
To understand carbon and all its forms, need to think about oxidation. 5/5/2015
REDUCTION-OXIDATION CHEMISTRY ‘Oxidation’ - measure of the surplus or deficit of electrons. Chemical reaction in which atoms have their oxidation number changed. Interaction between oxygen molecules and all the different substances they may contact, from metal to living tissue. Most elements have more than one possible oxidation state. 5/5/2015
P. 90 REDUCTION-OXIDATION CHEMISTRY OxidizedIntermediateReduced Simplest example CO 2 CH 2 0CH 4 C oxidation state +40-4 General Category Inorganic carbon CarbohydratesHydrocarbons 5/5/2015
‘ Oxidation’ is a measure of the surplus or deficit of electrons. Oxygen atoms each want to steal 2 electrons. Gives it its most stable electronic configuration. CO 2 – oxygen takes 4 electrons (+4) CH 4 – hydrogen atoms each give 1 electron to carbon (-4) CH 2 O – C gains 2 from H but give 2 to O C has many oxidation states so we group them into families. 5/5/2015
Most of the C on Earth 1. Inorganic (oxidized) carbon - Most of the C on Earth Most stable form; CaCO 3 (Limestone) Dissolved in oceans 2. Organic Carbon (reduced & intermediate) - Hydrocarbons Oil Natural gas 3. Carbohydrates (life is comprised of C in the intermediate state) Sugars
Life on Earth is based on the ‘nifty trick’ of harvesting energy from the sun and storing it by creating organic carbon from inorganic (oxidized) carbon. CO 2 + H 2 O + energy CH 2 O + O 2 Photosynthesis – forward direction of eqn (plants) Respiration – backward direction of eqn (consumers)
PHOTOSYNTHESIS Serves 2 purposes in the biosphere: uses carbon in the oxidation state stores energy from the sun in the form of organic carbon Nearly all of the organic carbon produced by photosynthesis is respired sooner or later. Peat deposits may hold organic carbon for thousands of years. 5/5/2015
But, on geologic scales, only organic carbon that ends up in ocean sediments escapes degradation back to CO 2 Earth has built up sizable pool of carbon in the reduced form of ocean sediments and sedimentary rocks (former ocean sed. on land). 5/5/2015
FIG. 8.1 CO2 in atm – tiniest fraction of all C on Earth Atm contains 700 gigatons of C Gton = 1 billion (10 9 ) metric tons 5/5/2015 Other sinks have more C All ‘breathe’ CO2, causing atm CO 2 to vary naturally. Timescales – 1 yr. to millions.
THE LAND BREATHES 2 forms of carbon associated with the landscape; 1.Terrestrial biosphere (plants/animals) - similar in size to atm 2.Soil Carbon Pool -more C than in living biosphere -highly varied place to place 5/5/2015
THE OCEAN BREATHES Larger sink than land surface or atm. Dissolved inorganic C not only dead, it’s oxidized. CO 2, H 2 CO 3 (carbonic acid) Dissolved organic carbon detritus Living C Fish, algae Flux – similar to land C is released from water in some areas and dissolves in others
EVEN THOUGH OCEAN AND LAND FLUXES ARE SIMILAR… Oceans don’t effect the CO 2 levels of atm as quickly as biosphere can. Atm absorbs CO 2 from oceans until the rate in and out balances. It takes hundreds of years for this equilibrium, because the oceans circulate so slowly. Glacial/interglacial cycle are an example of how oceans effect atm CO 2 Ice age every 150 million years Interglacial last 10,000 years Very different timescale than atm/land flux!! 5/5/2015
Ice core data shows changes in CO 2 Glacial intervals 180 – 200 ppm CO 2 Interglacial 260 – 280 ppm (preindustrial) No one is sure why the CO 2 cycles up and down, but the oceans are thought to be the source.
THE ROCKS BREATHE Sedimentary rock carbon pool largest Limestone (CaCO 3 ) + some organic C (Kerogen) Fossil Fuels Flux is very small!! But sink is HUGE! 500x atm/land combined 5/5/2015
UREY REACTION CaSiO 3 + CO 2 CaCO 3 + SiO 2 Silicate rocks are weathered to produce sedimentary rocks. Flux is extremely small But, if degassing stopped CO 2 would be gone from atm in a few hundred thousand years. 5/5/2015 Takes CO 2 out of atm Puts CO 2 back into atm
THE CARBONATE-SILICATE CYCLE Also known as the Urey Reaction Rainfall acts to "wash" CO 2 out of the atmosphere in the form of carbonic acid: CO 2 (gas) + H 2 O (liquid) --> H 2 CO 3 (carbonic acid) The carbonic acid weathers the rocks on the Earth's surface, releasing ions of calcium (Ca ++ ) and bicarbonate (HCO - 3 ) into the oceans. 5/5/2015
These combine into calcium carbonate (CaCO 3 ) on the sea floor either through formation of carbonate rocks living organisms making carbonate shells The calcium carbonate is eventually subducted down into the Earth (via plate tectonics), where high temps and pressures convert it back to CO 2 gas. CO 2 gas gets outgassed from volcanos back into the atmosphere. 5/5/2015
TAKE HOME POINTS Most stable form of C is oxidized as CO 2 or CaCO 3 Photosynthesis stores energy by producing organic C There is less C in atm than any other sink. Land and ocean sinks effect atm C, seasonally for land, 100,000 year scale for oceans. Flux from sed. rock sink is small (weathering) though size of this sink is the largest. 5/5/2015