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
Burden: amount of material in reservoir Water Cycle Box Model Source/Sink: flow rate into/out of reservoir Reservoir: region where material stored; each box
There s ~ 1.3x10 18 m 3 of H 2 O in the oceans. About 3.6x10 15 m 3 of H 2 O per year evaporate from the oceans. How long does the average H 2 O molecule reside in the ocean? 1. 36 years 2. 360 years 3. 3600 years 61% 35% 5% 36 years 360 years 3600 years
Precipitable Water Distribution Precipitable water greatest over oceans, in tropics.
Spatially Resolved Precipitation Rate Subsiding branches of Hadley Cells
Precipitation Rate Minus Evaporation Rate green (positive): net water gain yellow/brown (negative): net water loss
Water Cycle and Terrestrial Biosphere Forest Precipitation Tundra Desert 0 o C Temperature Grassland
Precipitation Changes with Global Warming Climate Model Predictions
Announcements Problem Set 4 Due Tuesday Feb 26 Group Choices by Friday Seminar on Thursday 12:30 310c ATG
Carbon Cycle Short-term biosphere-driven cycle Terrestrial biosphere Marine biosphere Long-term inorganic cycle Weathering-volcanism thermostat
Global Biogeochemical Cycles Reduced gas Oxidation Oxidized gas/ particle EARTH SURFACE Emission Uptake Deposition Reduction
Atmospheric CO 2 Seasonal Cycle CO2 Mixing Ratio (ppm) at Mauna Loa 350 348 346 344 342 340 338 336 334 332 Monthly Mean CO 2 Mixing Ratio 330 1980 1981 1982 1983 1984 1985 Time Atmosphere responds to biosphere on short timescales
Mass Units of Geologic Scale 1 Gigaton = 1x10 9 tons = 1x10 12 kg = 1 x 10 15 grams = 1 Petagram 1 Gigaton = 1 Petagram
Terrestrial Biosphere C Cycle Flows in units of Gtons C per year NPP: 60 Living Biomass 750 Gtons Atmosphere 780 Gtons 52 Decay/resp: 49 Litter 110 Gtons 8 3 Decay/resp: 11 Steady State? Longest lifetime? Shortest lifetime? Soil 2000 Gtons
The effect of deforestation on atmospheric CO 2 is 1. to increase it (source) 2. to decrease it (sink) 3. negligible 94% 5% 2% to increase it (source) to decrease it (sink) negligible
Under conditions of higher CO 2 (and sufficient nutrient supply), plants have been shown to increase photosynthesis rates. 1. Positive feedback 2. Negative feedback 3. Not a feedback 27% 58% 15% Positive feedback Negative feedback Not a feedback
Marine Organic C Cycle CO 2 Surface Ocean Deeper Ocean Photosynthesis CO 2(aq) + nutrients decay death/fecal matter OrgC sinks OrgC and nutrients O 2 CO 2(aq) a tiny bit to sediments
Biological OrgC Pump: Key Points 1. Surface depleted (relatively) in C and nutrients 2. Deep ocean enriched in C and nutrients 3. Atmospheric CO 2 responds to net pumping CO 2 and nutrients pumped down by biota Surface Ocean Thermo-Haline Circulation ~1000 yrs Deeper Ocean OrgC + O 2 CO 2(aq)
Marine Productivity Global map of ocean color from SEAWIFS satellite chlorophyll phytoplankton (where the nutrients are) remember upwelling and convection?
Reservoirs of (Inorganic) Carbon Atmosphere 790 Gtons Mainly as CO 2 Ocean 3.7x10 4 Gtons Mainly as HCO 3 - Lithosphere 4x10 7 Gtons Mainly as CaCO 3 Carbon in the oceans is mostly in an inorganic form
Shell Formation CO 2-3 + Ca2+Shell formation (CaCO 3(s) ) Surface Ocean Slow THC DIC slow CaCO 3(s) death/shells sink Deep Ocean Small amnt to sediments
Carbonate shell formation the ocean s capacity to take up atmospheric CO 2 1. increases 2. decreases 82% 18% increases decreases
The Ultimate Inorg C Cycle CaSiO 3 + CO 2 CaCO 3 + SiO 2
Silicate Weathering CaSiO 3 + CO 2 CaCO 3 + SiO 2 Rain/runoff CO 2 (atm) CaSiO 3 Rock CaCO 3 + SiO 2 CaSiO 3 Rock Ca 2+ CO 3 2- SiO 2 Chemical Weathering Rate Faster with higher CO 2, higher T, higher rainfall Oceans
Volcanic Degassing Volcanism causes reverse of weathering HEAT CaSiO 3 + CO 2 CaCO 3 + SiO 2 Tectonic activity converts CaCO 3 rocks back to silicate rocks in the mantle (magma). CO 2 released finds way to atmosphere via vents
Silicate Weathering Thermostat CO 2 Chemical weathering CaSiO 3 CaCO 3 + SiO 2 Precip/runoff CaCO 3 + SiO 2 burial CaCO 3 + SiO 2 CaCO 3 + SiO 2 CaSiO 3 + CO 2 This cycle operates on 0.5 1 million year timescale.
Is the silicate weathering volcanism InorgC cycle a positive or negative feedback? 1. Positive 2. Negative 58% 42% Positive Negative
Silicate Weathering Feedback Negative Feedback Stabilizing Climate - Initial Forcing + Silicate CO 2 Weathering Rate + + Temperature/ Precipitation
Does the silicate weathering feedback loop explain the glacial-interglacial cycling of atmospheric CO 2? 1. Yes 2. No 55% 45% Yes No