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Guiding Questions• What are the chemical reservoirs in the Earth system? • What is the difference between photosynthesis and respiration?• What happens to sugars that plants produce?• How does burial of dead plant tissue affect atmospheric CO2
and O2?• Where is organic carbon buried in large quantities?• How can carbon isotopes reveal the geologic history of carbon
burial? • How does weathering affect atmospheric CO2?
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Major Chemical Cycles• Greenhouse gases
– Atmospheric gases that trap warming solar radiation near Earth’s surface
– Climate change throughout Earth’s history
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Chemical Reservoirs• Bodies of chemical
entities that occupy particular spaces– Atmosphere– Oceans– Portion of crust– Biomass
• Flux– Expansion and contraction
of reservoirs with changes in rates at which elements or compounds flow through them
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• Feedbacks– Negative feedback
• Opposes expansion
– Positive feedback• Accelerates
expansion
Chemical Reservoirs
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Carbon Dioxide, Oxygen and Biological Processes
• Photosynthesis- respiration cycle– Water– CO2
• Photosynthesis– Captures energy– Creates sugars– Oxygen is a by-product
• Respiration– Releases energy through
oxidation of reduced carbon
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Carbon Dioxide, Oxygen and Biological Processes
• Plants remove CO2
for growth and reproduction– Plants:
• Are consumed• Decay• Are buried in
sediment
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Carbon Dioxide, Oxygen and Biological Processes
• Respiration– Gases are exchanged with
the environment– Animals respire to gain
energy from sugars from plants
• Plant and animals are in balance– To increase animals, must
increase plants – Double biomass, double O2
and CO2 fluxes
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Carbon Dioxide, Oxygen and Biological Processes
• Decomposers– Break down dead
organic debris not consumed by animals
– Bacteria, Fungi• Use respiration to
break down tissues
– Extract O2, release CO2
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Carbon Dioxide, Oxygen and Biological Processes
• Burial of plant debris affects atmospheric chemistry
• Removal of plants from system– Burial
• Reservoir of reduced C
• Erosion usually balances it
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Carbon Dioxide, Oxygen and Biological Processes
• Change in burial can increase atmospheric concentrations– O2 increases when carbon is
buried• Decomposers cannot act on
reduced carbon• Oxygen remains in atmosphere• In marine systems, aquatic
planktonic algae fulfills roles of plants
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Carbon Dioxide, Oxygen and Biological Processes
• Carbon is introduced to oceans through rivers
• Marine plankton provide additional carbon
• Anoxia aids in burial of carbon– Virtual absence of CO2
• Anoxia was widespread in mid-Cretaceous– Organic-rich mud became
black shales
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Carbon Isotopes• Carbon isotopes can trace some
aspects of atmospheric chemistry
• 12C used by plants in greater proportion than present in the atmosphere
• Rapid burial impacts atmospheric isotopic ratio– Remove proportionately more 12C– Atmosphere enriched in 13C– Oceans follow
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Carbon Isotopes
• Isotopes in limestone (CaCO3)
• Phanerozoic record indicates intervals of great change– Late Carboniferous
swamps• Excess 13C in
atmosphere and oceans
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Carbon Isotopes
• Marine phytoplankton– Preserved in times
of anoxia– Store 12C– Enrich oceans in
13C
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Carbon Isotopes
• Weathering of CaCO3 releases Ca++ and HCO3-
– Carried to oceans– Precipitate limestone
skeletal material– Carbon is stored for
long time period– Released upon
subduction
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Weathering and CO2• Mountain Building
– Weathering and erosion require CO2
• Temperature– Higher temperatures increase rates
of chemical reactions
• Precipitation– Aids in chemical weathering– Continental configuration pattern
• Vegetation– Weathering in forests higher
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Phanerozoic Trends in CO2
• Computer model for CO2
• Paleozoic Era– Devonian decrease
• Widespread forests• Increase in weathering
– Carboniferous• Burial in swamps• Aided in Gondwanaland
glaciation
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• Mesozoic Era– Reduced mountain
building• Reduced weathering• Increased CO2
– Evolution of calcareous nannoplankton and foraminifera
• Pelagic oozes• Stored CO2 as CaCO2
Phanerozoic Trends in CO2
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• Cenozoic Era– Increased mountain
building• Increased weathering
• Decreased CO2
– Increased aridity• Reduced groundwater flow,
further decreased weathering
• Decreased CO2
• Aided in glaciation
Phanerozoic Trends in CO2
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Frozen Methane• CH4
– Most produced by Archean prokaryotes
• Herbivore flatulence– Significant warming
• Stored frozen on sea floor and deep under tundra– Low temperature, high
pressure formation– Also found on continental
slope (400–1000 m w.d.)
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Frozen Methane• Release of frozen methane releases
carbon– Water at depth warms– Rapid release of greenhouse gases
(methane)– Positive feedback
• Continue to warm• Signal is 12C dominated
• Early Jurassic (Toarcian)– Climate warmed– Ocean circulation dropped– Black muds predominated
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Role of Negative Feedbacks• Temperature
– High CO2
• High temperatures• Increase weathering• Decrease CO2
– Low CO2
• Temperatures decrease• Weathering decreases• Increase CO2
• Precipitation– Ocean temperatures impact moisture
• Warm oceans decrease aridity, aid forests
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Oxygen Isotopes• Common isotopes
– 16O and 18O
• Organisms incorporate oxygen into shells
• Ratio depends on– Temperature– Salinity– Ratio of water
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Oxygen Isotopes• Temperature
– More 18O at lower temperatures
– Value can change with diagenesis and recrystallization
• Rudists– Cretaceous reef builders– Indicates seasonal
temperature range from 22–32°C
• Warmer than today
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Oxygen Isotopes• Precipitate skeletons in
proportion to water they live in
• Salinity and glaciers affect seawater ratios– Salinity increases 18O
abundance– Glaciers increase 16O
abundance in ice on land, and 18O abundance in seawater
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Oxygen Isotopes• Late Pleistocene record of glaciation
– Higher 18O/ 16O during glacial periods– Lower 18O/ 16O during interglacial periods
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Skeletal Mineralogy• Type of CaCO3 to precipitate
depends on abundance of Ca++ and Mg ++
• Mg, Ca swap in calcite– High-magnesium calcite– Mg too small to fit into
aragonite lattice
• High Mg ++/Ca ++ precipitates aragonite and high-magnesium calcite
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• Mid-ocean ridge ion exchange system– Extract Mg++ from seawater,
release Ca ++ to it– Lower Mg ++/Ca ++ when
ridges are abundant
• Correlates with sea-level change– High MOR volume, high
sea level
Skeletal Mineralogy
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Skeletal Mineralogy• Upper Cretaceous
Series chalks– Prolific calcareous
nannofossils– Accumulated rapidly
• 1 mm/year
– Driven by very low ratio of Mg++ to Ca ++
• Easy precipitation of calcite