chapter_12 Part 2

chapter_12 Part 2 - IV The long Term Climate Record IV a...

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Unformatted text preview: IV. The long Term Climate Record IV. a. Geological indicators of Paleoclimate i. Recent periods 1. Deep sea sediment cores 2. Only good for 200 m.y. 3. Fossil record (estimate temp and precip) ii. Precambrian periods 1. Oxygen isotopes in rocks 2. Results conflict with sun’s dimness and glacial Results periods periods 3. Earth’s mean temperature was 70°C during Archean 4. 55-60°C during proterozoic IV. The long Term Climate Record Record b. Evidence of past glaciations i. Time scale of billions of years ii. Glacial deposits 1. Tillites and Moraines 2. Glacial Striations 3. Dropstones and Ice-Rafting 3. IV. The long Term Climate Record Record c. The long-term glacial record i. Mid-Archean glaciation 2.9 bya ii. Huronian glaciation 2.4 bya iii. Neoproterozoic 730 and 610 mya iv. Late Ordovician 440 mya v. Permian-Carboniferous 280 mya vi. Pleistocene 3 mya IV. The long Term Climate Record IV. d. Why did Earth experience major d. glaciations in the midst of an extended, ice-free stretch of history ice-free i. The rise of O2 (Huronian) ii. The rise of methane and organic haze(MidArchean) iii. Lower CO2 concentrations IV. The long Term Climate Record IV. e. Low-latitude glaciation: snowball Earth i. a. b. c. d. Low values of CO2 Increase organic carbon burial or some other process Significant amount of continental area in tropics Silicate weathering draws down CO2 levels When continents are at mid-high latitudes the feedback prevents global glaciation ii. a. Colder temperatures and polar ice sheets move south Once they reach ~20° latitude, ice albedo feedback becomes strong iii. iv. i. ii. iii. iv. Silicate weathering ceases and volcanic CO2 accumulates in atmosphere Ice melts over a to m.y. period - (300 times present CO2) Ice-albedo feedback works in opposite direction Ice cover would disappear in a few 1,000 years. CO2 rich atmosphere, lower albedo, warm surface temperature, and increased rates of silicate weathering rates This decreases CO2 concentration to restore the climate state V. Variations in CO2 & Climate during the Phanerozoic the a. CO2 and Climate during the Paleozoic Era i. Cambrian warmer then today ii. Mostly ice-free except for late Ordovician iii. Cooling after the Carboniferous iv. Why did the climate cool? 1. We’ve seen trade offs between solar luminosity and green house gases 1. By this time atmosphere was well oxygenated 1. CH4 probably low 2. Cooling probably result of decreased CO2 a. b. c. carbonate- silicate cycle? Plant? Formation of coal beds 1. Double organic carbon burial rate 2. Increase O2 3. 3. Descrease CO2 V. Variations in CO2 & Climate during the Phanerozoic the b. The Warm Mesozoic Era ii. Age of the dinosaurs . Age ii. Considered warmer than today iii. Ocean also warmer than today V. Variations in CO2 & Climate during the Phanerozoic the b. The Warm Mesozoic Era ii. Age of the dinosaurs . Age ii. Considered warmer than today iii. Ocean also warmer than today V. Variations in CO2 & Climate during the Phanerozoic the b. The Warm Mesozoic Era iv. What kept the climate warm? 1. higher CO2 by a factor of 4 2. higher rate of seafloor spreading 3. subduction and increased carbonate 3. metamorphism leading to more CO2 outgassing outgassing 4. higher sea level and less land area so 4. less silicate weathering less V. Variations in CO2 & Climate during the Phanerozoic the c. Carbon isotopic evidence of High c. Mesozoic CO2 levels Mesozoic c. Carbon isotopic evidence of High Mesozoic c. CO2 levels CO2 i. ii. Organisms take up C12 faster than C13 Take up is faster if CO2 is abundant V. Variations in CO2 & Climate during the Phanerozoic the iii. Photosynthetically created organic matter low Photosynthetically C13/C14 ratio (if CO2 was abundant) C13/C14 iv. If CO2 is scare, organisms use the available isotope isotope C13/C14 ratio is higher V. Variations in CO2 & Climate during the Phanerozoic Phanerozoic d. Other possible influences on the Mesozoic Climate i. small latitudinal temperature gradient ii. Factors 1. no polar ice 2. more effect heat transport to the poles via ocean currents and more winds winds a. Backward Thermohaline circulation b. Warm, high salinity deep water formed at low latitudes and Warm, upwells towards poles upwells c. Warmed the climate through evaporation (especially poles) 3. Hadley cell extended poleward 4. Less dimethly sulfide a. Reduced production of clouds due to less CCN (fewer and Reduced thinner) thinner) b. Less biological productivity (reduced nutrient supply in Less upwelling) upwelling) c. Strong thermocline acts as a barrier to upwelling d. Global warming and increased warming near poles Global V. Variations in CO2 & Climate during the Phanerozoic the e. Cooling during the Cenozoic Era i. Cooling started about 80 mya ii. Decrease in mid ocean ridge spreading rates Decrease and a reduction in atmospheric CO2 and iii.Cooling accelerated during the Oligocene but Cooling does not correlate with higher spreading rates does iv.Carbonate-silicate cycle perturbed by plate Carbonate-silicate tectonics tectonics Himalaya Mountains Himalaya were a new surface for weathering to occur over occur Creation of the Creation Tibetan Plateau provided enhanced uplift for precipitation uplift Monsoonal rains Monsoonal increase weathering rates rates Acceleration of Acceleration silicate weathering Reduction in CO2 Reduction levels levels Climate & Plate Tectonics Climate Main influence of plate tectonics on Main climate is indirect climate Changes the carbonate-silicate cycle Causes increases or decreases in Causes atmospheric CO2 concentrations atmospheric Indirectly impacts the greenhouse effect and Indirectly climate climate These changes along with changes in solar These luminosity account for main features of the long-term climate record long-term ...
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