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This Week: Biogeochemical Cycles

This Week: Biogeochemical Cycles. Hydrologic Cycle Carbon Cycle. Announcements. Reading: Chapters 4 (p. 74 – 81) and 8 Another Problem Set (Due next Tuesday) Exam 2: Friday Feb 29 My office hours today and next week rescheduled to Thurs 3 - 4 pm. Water Cycle “Box Model”.

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This Week: Biogeochemical Cycles

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  1. This Week: Biogeochemical Cycles Hydrologic Cycle Carbon Cycle

  2. Announcements • Reading: Chapters 4 (p. 74 – 81) and 8 • Another Problem Set (Due next Tuesday) • Exam 2: Friday Feb 29 • My office hours today and next week rescheduled to Thurs 3 - 4 pm

  3. Water Cycle “Box Model” Burden: amount of material in reservoir Source/Sink: flow rate into/out of reservoir Reservoir: region where material stored; each box

  4. There’s ~ 1.3x1018 m3 of H2O in the oceans. About 3.6x1015 m3 of H2O per year evaporate from the oceans. How long does the average H2O molecule reside in the ocean? • 36 years • 360 years • 3600 years

  5. Precipitable Water Distribution Precipitable water greatest over oceans, in tropics.

  6. Spatially Resolved Precipitation Rate Subsiding branches of Hadley Cells

  7. Precipitation Rate Minus Evaporation Rate green (positive): net water gain yellow/brown (negative): net water loss

  8. Water Cycle and Terrestrial Biosphere Forest Grassland Tundra Precipitation Desert 0oC Temperature

  9. Precipitation Changes with Global Warming Climate Model Predictions

  10. Announcements • Problem Set 4 Due Tuesday Feb 26 • Group Choices by Friday • Seminar on Thursday 12:30 310c ATG

  11. Carbon Cycle • Short-term biosphere-driven cycle • Terrestrial biosphere • Marine biosphere • Long-term inorganic cycle • Weathering-volcanism thermostat

  12. Global Biogeochemical Cycles Oxidation Oxidized gas/ particle Reduced gas Emission Deposition Uptake EARTH SURFACE Reduction

  13. Atmospheric CO2 Seasonal Cycle Atmosphere responds to biosphere on short timescales

  14. Mass Units of Geologic Scale • 1 Gigaton = 1x109 tons = 1x1012 kg = 1 x 1015 grams = 1 Petagram • 1 Gigaton = 1 Petagram

  15. Terrestrial Biosphere C Cycle Flows in units of Gtons C per year Atmosphere 780 Gtons NPP: 60 Decay/resp: 49 52 Living Biomass 750 Gtons Litter 110 Gtons Decay/resp: 11 8 3 Steady State? Longest lifetime? Shortest lifetime? Soil 2000 Gtons

  16. The effect of deforestation on atmospheric CO2 is • to increase it (source) • to decrease it (sink) • negligible

  17. Under conditions of higher CO2 (and sufficient nutrient supply), plants have been shown to increase photosynthesis rates. • Positive feedback • Negative feedback • Not a feedback

  18. Marine Organic C Cycle CO2 death/fecal matter OrgC sinks OrgC and nutrients O2 CO2(aq) a tiny bit to sediments Photosynthesis Surface Ocean CO2(aq) + nutrients decay Deeper Ocean

  19. Biological OrgC Pump: Key Points 1. Surface depleted (relatively) in C and nutrients 2. Deep ocean enriched in C and nutrients 3. Atmospheric CO2 responds to net pumping CO2 and nutrients pumped down by biota Thermo-Haline Circulation ~1000 yrs Surface Ocean Deeper Ocean OrgC + O2 CO2(aq)

  20. Marine Productivity Global map of ocean color from SEAWIFS satellite chlorophyll phytoplankton (where the nutrients are) remember upwelling and convection?

  21. Reservoirs of (Inorganic) Carbon Atmosphere 790 Gtons Mainly as CO2 Ocean 3.7x104 Gtons Mainly as HCO3- Lithosphere 4x107 Gtons Mainly as CaCO3 Carbon in the oceans is mostly in an inorganic form

  22. Shell Formation Slow THC death/shells sink slow DIC CaCO3(s) Small amnt to sediments Shell formation (CaCO3(s)) CO32- + Ca2+ Surface Ocean Deep Ocean

  23. Carbonate shell formation ___________ the ocean’s capacity to take up atmospheric CO2 • increases • decreases

  24. The “Ultimate” Inorg C Cycle Chemical Weathering CaSiO3 + CO2 CaCO3 + SiO2 Volcanism

  25. Silicate Weathering CaSiO3 + CO2 CaCO3 + SiO2 Rain/runoff Ca2+ CO32- SiO2 CO2 (atm) CaCO3 + SiO2 CaSiO3 Rock CaSiO3 Rock Chemical Weathering Rate Faster with higher CO2, higher T, higher rainfall Oceans

  26. Volcanic Degassing Volcanism causes reverse of weathering HEAT CaSiO3 + CO2CaCO3 + SiO2 Tectonic activity converts CaCO3 rocks back to silicate rocks in the mantle (magma). CO2 released finds way to atmosphere via vents

  27. Silicate Weathering “Thermostat” CO2 Chemical weathering CaSiO3 CaCO3 + SiO2 Precip/runoff CaCO3 +SiO2 burial CaCO3 + SiO2 CaCO3 + SiO2 CaSiO3 + CO2 This cycle operates on 0.5 – 1 million year timescale.

  28. Is the silicate weathering – volcanism InorgC cycle a positive or negative feedback? • Positive • Negative

  29. Silicate Weathering Feedback + Temperature/ Precipitation Negative Feedback—Stabilizing Climate - CO2 Silicate Weathering Rate + Initial Forcing +

  30. Does the silicate weathering feedback loop explain the glacial-interglacial cycling of atmospheric CO2? • Yes • No

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