1 / 32

Major Chemical Cycles in Earth's System

Explore the chemical reservoirs in Earth's system, the role of photosynthesis and respiration, the burial of plant tissue, and the impact of weathering on atmospheric CO2. Discover how carbon isotopes reveal the geologic history of carbon burial and the influence of greenhouse gases on climate change.

danielsanders
Download Presentation

Major Chemical Cycles in Earth's System

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Chapter 10 Major Chemical Cycles

  2. 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?

  3. Major Chemical Cycles • Greenhouse gases • Atmospheric gases that trap warming solar radiation near Earth’s surface • Climate change throughout Earth’s history

  4. 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

  5. Chemical Reservoirs • Feedbacks • Negative feedback • Opposes expansion • Positive feedback • Accelerates expansion

  6. 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

  7. Carbon Dioxide, Oxygen and Biological Processes • Plants remove CO2 for growth and reproduction • Plants: • Are consumed • Decay • Are buried in sediment

  8. 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

  9. 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

  10. Burial of plant debris affects atmospheric chemistry Removal of plants from system Burial Reservoir of reduced C Erosion usually balances it Carbon Dioxide, Oxygen and Biological Processes

  11. 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

  12. 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

  13. 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

  14. Carbon Isotopes • Isotopes in limestone (CaCO3) • Phanerozoic record indicates intervals of great change • Late Carboniferous swamps • Excess 13C in atmosphere and oceans

  15. Carbon Isotopes • Marine phytoplankton • Preserved in times of anoxia • Store 12C • Enrich oceans in 13C

  16. 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

  17. 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

  18. 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

  19. Phanerozoic Trends in CO2 • Mesozoic Era • Reduced mountain building • Reduced weathering • Increased CO2 • Evolution of calcareous nannoplankton and foraminifera • Pelagic oozes • Stored CO2 as CaCO2

  20. Phanerozoic Trends in CO2 • Cenozoic Era • Increased mountain building • Increased weathering • Decreased CO2 • Increased aridity • Reduced groundwater flow, further decreased weathering • Decreased CO2 • Aided in glaciation

  21. 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.)

  22. 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

  23. 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

  24. Oxygen Isotopes • Common isotopes • 16O and 18O • Organisms incorporate oxygen into shells • Ratio depends on • Temperature • Salinity • Ratio of water

  25. 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

  26. 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

  27. Oxygen Isotopes • Late Pleistocene record of glaciation • Higher 18O/ 16O during glacial periods • Lower 18O/ 16O during interglacial periods

  28. 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

  29. Skeletal Mineralogy • 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

  30. 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

More Related