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The Rise of Atmospheric O2 Images removed due to The Faint Young copyright restrictions. Sun Paradox & The Geochemical C Cycle & Climate on Geologic Time Scales 12.007 Geobiology Paleoclimate Lec. 1 Spring 2007 Paleoclimate: outline • Incoming and outgoing • Climate change examples: radiation balance; greenhouse – Permo-Carboniferous glaciations effect • Continental arrangement • Land Plants and carbon cycle • Faint Young Sun Paradox – Mesozoic warmth: • Global carbon cycle • warmer equator, decreased • Weathering and “reverse equator-pole temperature gradient, ?higher CO ? weathering” 2 – Cenozoic cooling • Snowball earth climate •? Lower CO2? (early maybe, but not considerations: can the earth later). Roles of mountain uplift, escape from a snowball? weathering, seafloor spreading rates? – Pleistocene glaciation cycles • Oxygen isotope paleoclimatology • Milankovitch insolation cycles • Ice cores and greenhouse gas changes • Abrupt climate change Image removed due to copyright restrictions. Please see Fig. 3 in Rottman, Gary, and George, Vanessa. “An Overview of the Solar Radiation and Climate Experiment (SORCE).” The Earth Observer 14 (May/June 2002): 17-22. Greenhouse Gases absorb IR radiation efficiently (1) Molecules acquire energy when they absorb photons. (2) This energy will be released later as re-emitted photons. (3) Atmospheric molecules are rotating rapidly (and in aggregate, randomly), so the re- emitted energy is random in direction. (4) So: half of the re-emitted radiation is directed back towards the earth. Image removed due to copyright restrictions. Please see Fig. 10.1.4 in Sarmiento, J. and Gruber, N. Ocean Biogeochemical Dynamics. Princeton, NJ: Princeton University Press, 2005. http://press.princeton.edu/chapters/s10_8223.pdf Contemporary Solar Variability Image removed due to copyright restrictions. Please see Fig. 9 in Fröhlich, C. “Solar Irradiance Variability since 1978.” Space Science Reviews 125 (August 2006): 53-65. •Contemporary Solar Variability ~0.1% •Associated with 11-year sunspot cycle Energ y Balan ce Greenhouse Gases Figure by MIT OCW. Courtesy of NASA http://www.nasa.gov/images/content/136048main_bm_012004.jpg Simple Planetary Energy Balance •Likely solution to FYSP requires understanding of Earth’s energy balance (& C cycle) 2πk 4 π 4 σ = = 5.67 •10−8 w m−2 °K −4 h3c2 15 Adapted from Kump et al. (1999) Energy Absorbed Adapted from Kump et al. (1999) Neither albedo nor geothermal heat flux changes can keep the earth from freezing w/ 30% lower S Adapted from Kump et al. (1999) Lower S compensated by larger greenhouse effect? Adapted from Kump et al. (1999) But: the atmosphere is a leaky greenhouse… If we assume that the atmospheric gas composition is what it is today, and then do the full radiative calculations assuming that the atmosphere does not convect, then the earth would be ~30°C warmer than it is. That is, the earth’s greenhouse effect is only ~50% efficient. The difference is due to convection: when the near-surface air warms up, it rises in the atmosphere and can lose radiation to space more effectively. Paleoclimate: outline • Incoming and outgoing • Climate change examples: radiation balance; greenhouse – Permo-Carboniferous glaciations effect • Continental arrangement • Land Plants and carbon cycle • Faint Young Sun Paradox – Mesozoic warmth: • Global carbon cycle • warmer equator, decreased • Weathering and “reverse equator-pole temperature gradient, weathering” ?higher CO2? – Cenozoic cooling • Snowball earth climate • ? Lower CO2? (early maybe, but considerations: can the earth not later). Roles of mountain uplift, escape from a snowball? weathering, seafloor spreading rates? – Pleistocene glaciation cycles • Oxygen isotope paleoclimatology • Milankovitch insolation cycles • Ice cores and greenhouse gas changes • Abrupt climate change The ‘Faint Young Sun Paradox’ Faint Faint Young Sun Paradox Young Sun Paradox 4 1H-->4He Incr. density= incr. luminosity Liquid H2O existed >3.5 Ga (sed. rocks, life, zircon δ18O) Enhanced CO2 Greenhouse Effect seems Necessary! Image removed due to copyright restrictions. Please see p. 94 in Kasting, James F., et al. “How Climate Evolved on the Terrestrial Planets.” Scientific American 256 (1988): 90-97. http://www.geosc.psu.edu/~kasting/PersonalPage/Pdf /Scientific_American_88.pdf shaded region shows greenhouse effect (incl. water vapor feedback and const. O2 of 340 ppm) PrecambrianPrecambrian ppCOCO22 EstimatesEstimates Image removed due to copyright restrictions. Please see Fig. 3 in Kaufman, Alan J., and Xiao, Shuhai. "High CO2 levels in the Proterozoic atmosphere estimated from analyses of individual microfossils." Nature 425 (September 18, 2003): 279-282. Earth’s Climate History: MostlyMostly sunnysunny withwith aa 10%10% Image removed due to chancechance ofof snowsnow copyright restrictions. Please see Kump, L. R., et al. The Earth System. Upper Saddle River, NJ: Pearson Prentice Hall, 1999. Image removed due to copyright restrictions. Please see Fig. 1 in Lubick, Naomi. “Palaeoclimatology: Snowball Fights.” Nature 417 (May 2, 2002): 12-13. •What caused these climate perturbations? Paleoclimate: outline • Incoming and outgoing • Climate change examples: radiation balance; greenhouse – Permo-Carboniferous glaciations effect • Continental arrangement • Land Plants and carbon cycle • Faint Young Sun Paradox – Mesozoic warmth: • Global carbon cycle • warmer equator, decreased • Weathering and “reverse equator-pole temperature gradient, weathering” ?higher CO2? – Cenozoic cooling • Snowball earth climate • ? Lower CO2? (early maybe, but considerations: can the earth not later). Roles of mountain uplift, escape from a snowball? weathering, seafloor spreading rates? – Pleistocene glaciation cycles • Oxygen isotope paleoclimatology • Milankovitch insolation cycles • Ice cores and greenhouse gas changes • Abrupt climate change Carbon Cycle: Strong driver of climate on geologic timescales Earth's Carbon Budget Biosphere, Oceans and Atmosphere 3.7x1018 moles Crust Corg Carbonate 1100 x 1018 5200 x 1018 mole mole Mantle 100,000 x 1018 mole CarbonCarbon Reservoirs,Reservoirs, FluxesFluxes andand ResidenceResidence TimesTimes Species Amount Residence Time (yr)* δ 13 C 18 (in units of 10 gC) %o PDB** Sedimentary carbonate-C 62400 342000000 ∼ 0 Sedimentary organic-C 15600 342000000 ∼ -24 Oceanic inorganic-C 42 385 ∼ +0.46 Necrotic-C 4.0 20-40 ∼ -27 Atmospheric-CO2 0.72 4 ∼ -7.5 Living terrestrial biomass 0.56 16 ∼ -27 Living marine biomass 0.007 0.1 ∼ -22 Rapid Turnover Steady State & Residence Time Steady State: Inflows = Outflows Any imbalance in I or O leads to changes in reservoir size Inflow: Outflow: 60 Gton C/yr Atmospheric CO2 60 Gton C/yr Respiration Photosynthesis 760 Gton C 1 Gton = 109 * 1000 kg = 1015 g The Residence time of a molecule is the average amount of time it is expected to remain in a given reservoir. Example: tR of atmospheric CO2 = 760/60 = 13 yr The bio-geochemical carbon cycle Paleoclimate: outline • Incoming and outgoing • Climate change examples: radiation balance; greenhouse – Permo-Carboniferous glaciations effect • Continental arrangement • Land Plants and carbon cycle • Faint Young Sun Paradox – Mesozoic warmth: • Global carbon cycle • warmer equator, decreased • Weathering and “reverse equator-pole temperature gradient, weathering” ?higher CO2? – Cenozoic cooling • Snowball earth climate • ? Lower CO2? (early maybe, but considerations: can the earth not later). Roles of mountain uplift, escape from a snowball? weathering, seafloor spreading rates? – Pleistocene glaciation cycles • Oxygen isotope paleoclimatology • Milankovitch insolation cycles • Ice cores and greenhouse gas changes • Abrupt climate change Chemical Weathering = chemical attack of rocks by dilute acid CO2 + H2O <---> “H2CO3” ---------------------------------------------- biogeochemical 1. Carbonate Weathering: carbon cycle #2 2+ - CaCO3 + “H2CO3” --> Ca + 2 HCO3 2. Silicate Weathering: 2+ - CaSiO3 + 2 “H2CO3” --> Ca + 2HCO3 + SiO2 + H2O ============================= • Carbonates weather faster than silicates Carbonate rocks Image removed due to copyright restrictions. weather faster than silicate rocks… Products of Image removed due to copyright restrictions. weathering Please see Kump, L. R., et al. The Earth System. Upper Saddle River, NJ: Pearson precipitated Prentice Hall, 1999. as CaCO3 & SiO2 in ocean CaCO3 weathering is cyclic (CO2 is not lost from the system), but calcium silicate weathering results in the loss of CO2 to solid CaCO3: CaCO3 weathering cycle CaCO3 weathering: 2+ - CaCO3+ CO2 + H2O => Ca + 2 HCO3 CaCO3 sedimentation: 2+ - Ca + 2 HCO3 => CaCO3 + CO2 + H2O Silicate weathering cycle(?) Silicate weathering: 2+ - CaSiO3 + 2 CO2 + 2H2O => Ca + Si(OH)4 + 2 HCO3 CaCO3 and SiO2 sedimentation: 2+ - Ca + 2 HCO3 + Si(OH)4 => CaCO3+ SiO2•2H2O + 1 CO2 + H2O The weathering of other aluminosilicates results in the loss of CO2 AND makes the ocean saltier and more alkaline: Potassium feldspar weathering “cycle” weathering: + - 2 KAl2Si2O8 + 2 CO2 + 2H2O => 2 K + 2 HCO3 + 2 Si(OH)4 + Al2O3 (solid) sedimentation: + - + - 2 K + 2 HCO3 + 2 Si(OH)4 + Al2O3 => 2 SiO2•2H2O+ Al2O3 + 2 K + 2 HCO3 Problem: As CO2 is buried as CaCO3 in sediments, why doesn’t CO2 eventually vanish from the atmosphere? (It would take only ~400,000 years of silicate weathering to consume all of the carbon in today’s ocean/atmosphere system) Net Reaction of Rock Weathering + Carbonate and Silica Precipitation in Ocean CaSiO3 + CO2 --> CaCO3 + SiO2 • CO consumed 2 Net reaction of • Would deplete atmospheric
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