Presentation on theme: "Carbon Cycle Adapted in part from lectures by Dr. Gerardo Chin-Leo, TESC Chautauqua UWA-6, Dr. E.J. Zita 9-11 July 2007 Fire, Air, and Water: Effects of."— Presentation transcript:
Carbon Cycle Adapted in part from lectures by Dr. Gerardo Chin-Leo, TESC Chautauqua UWA-6, Dr. E.J. Zita 9-11 July 2007 Fire, Air, and Water: Effects of the Sun, Atmosphere, and Oceans in Climate Change and Global Warming
Milankovitch Mechanism is not a complete explanation for glaciation cycles…
Evidence for carbon feedback contribution to long-term climate regulation
Feedback Loop Linking Glaciations, Atmospheric CO 2 and Phytoplankton C-burial Interglacial Period Small Ice Caps Large Exposed Continental Mass More Nutrients to the Sea From Land Erosion High Productivity High C-Burial Low CO 2 Cool Temperatures Ice Age Large Ice Caps Small Exposed Continental Mass Few Nutrients to the Sea From Land Erosion Low Productivity Low C-Burial High CO 2 Warm Temperatures
Chemistry of Inorganic C in Water Carbonate buffering and pH CO 2 + H 2 O H 2 CO 3- (carbonic acid) H 2 CO 3 H + + HCO 2- (bicarbonate) HCO 3- H + + CO 3 2+ (carbonate)
Atmospheric O 2 and the C Cycle
Isotope composition of carbonate sediments reveals the net production of O 2 Photosynthesis selects C 12 over C 13, thus organic material is depleted (isotopically lighter) in C 13 During times of increased net O 2 production, more organic C is buried, thus atmospheric and oceanic C becomes richer (isotopically heavier) in C 13 This enrichment of C 13 in the environment is reflected in carbonate sediments Assuming a constant total mass of C 13 and C 12, the faster the organic C is buried (more O 2 accumulates) the heavier (enriched C 13) the carbonates become
13 C Isotope Signature Scale (Del) C 13 in ‰ (C 13 / C 12 ) sample - (C 13 / C 12 ) standard = X 1000 (C 13 / C 12 ) standard Example: [( – )/ ]*1000 = 1.78 ( C 13 / C 12 ) standard is the ratio in a standard sample of the fossil invertebrate Belemnitella americana (Cretaceous Peedee formation in South Carolina)
Evidence for the relative constancy of O 2 in the atmosphere There is evidence for the existence of forests dating back to ~360 mya. These forests need O 2 to exist There is evidence of forest fires ever since (charcoal in sediment) Forest fires cannot occur if O 2 < 13% If O 2 > 35% fires burn so fiercely that all forests would have disappeared Consequently, O 2 is believed to have remained in the range of 13-35% (current concentration is 21%)
13 C as an Indicator of Ancient CO 2 Levels 13 C is taken by plants slower than 12 C. Thus organic matter is depleted in 13 C compared to CO 2. However, when CO 2 concentrations are low, plants do not discriminate 13 C from 12 C as much as when CO 2 levels are high. Thus, the 13 C: 12 C ratio in organic matter under low CO 2 levels is higher (more 13 C relative to 12 C) than during times of high CO 2 levels (more 13 C relative to 12 C).
Use of 13 C in Ecology 13 C is fractionated (or discriminated) by physical processes (e.g evaporation/precipitation). There is less 13 C in atmospheric CO 2 than in dissolved CO 2 (bicarbonate) Consequently land plants are isotopically lighter than aquatic plants There is another fractionation of 13 C based on the photosynthetic metabolism of the plant (C3, C4 or CAM). Consequently organic matter from C3, C4 or CAM plants can be distinguished from each other based on their - 13 C signatures.
Through condensation-evaporation, water gets isotopically “lighter” as it moves to higher latitudes. Polar ice is depleted in 18 O.
18 O indicates ancient ice volumes and temperatures Volume: Evaporation/precipitation and formation of polar ice excludes 18 O. During ice ages the concentration of 18 O in the oceans increases. Benthic foraminifera fossils show the 18 O: 16 O of ancient seawater Paleothermometer: the formation of CaCO 3 by foraminifera excludes 18 O as a function of temperature. Benthic foraminifera form shells under constant temperature thus their 18 O: 16 O reflects the isotope composition of the water. Planktonic foraminifera experience temperature fluctuations and these are recorded as changes in their 18 O: 16 O relative to benthic forms
Relationship Between 18 O Content and Temperature Water 18 O is derived from benthic (deep) foraminifera. Carbonate 18 O is derived from planktonic foraminifera
From: Introduction to Marine Biogeochemistry -Libes (1992)
Evidence that Increasing Atmospheric CO 2 is Anthropogenic Increase consistent with onset and development of industrialization Magnitude and rate of increase consistent with magnitude and rates of fossil fuels consumption Suess effect: Lowering of 14 C: 12 C in CO 2 by the input of “old” carbon from fossil fuel burning (Higher 14 C when lower solar magnetic activity shields Earth less from incoming cosmic rays)
Lower recent C 14 /C 12 from fossil fuel burning Evidence of anthropogenic source for greenhouse gases Little Ice Age: low solar magnetic activity throughout?
Solar magnetic activity and C 14 production Cosmic rays excite N 14 → decays to C 14 Solar max: magnetic solar wind sweeps away cosmic rays → less *N 14 → less C 14
Car & Driver: Global warming is natural Earth has been getting steadily warmer since the last ice age – a few more degrees would be nice All CO 2 is the same, whether it comes from a Porsche or your lungs – anthropogenic CO 2 does no extra harm There’s 30 times as much natural CO 2 as man-made Water vapor is the dominant greenhouse gas, so why worry so much about CO 2 ? We can’t do anything about water vapor, so Kyoto targeting CO 2 is trivial. Discuss and analyze these claims, given what we now know.
Inconvenient truth: accelerated GW is anthropogenic Bad news: we can’t do anything about Milankovitch cycles Increasing solar luminosity Increasing solar magnetic activity Good news: We CAN do something about anthropogenic emissions of greenhouse gases Oceans and plants will absorb as much CO 2 as they can.