This Week: Biogeochemical Cycles. Hydrologic Cycle Carbon Cycle

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Maria Mitchell
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1 This Week: Biogeochemical Cycles Hydrologic Cycle Carbon Cycle

2 Announcements Reading: Chapters 4 (p ) 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 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

4 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? years years years 61% 35% 5% 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 Precipitation Tundra Desert 0 o C Temperature Grassland

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 Reduced gas Oxidation Oxidized gas/ particle EARTH SURFACE Emission Uptake Deposition Reduction

13 Atmospheric CO 2 Seasonal Cycle CO2 Mixing Ratio (ppm) at Mauna Loa Monthly Mean CO 2 Mixing Ratio Time Atmosphere responds to biosphere on short timescales

14 Mass Units of Geologic Scale 1 Gigaton = 1x10 9 tons = 1x10 12 kg = 1 x grams = 1 Petagram 1 Gigaton = 1 Petagram

15 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

16 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

17 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

18 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

19 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)

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 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

22 Shell Formation CO Ca2+Shell formation (CaCO 3(s) ) Surface Ocean Slow THC DIC slow CaCO 3(s) death/shells sink Deep Ocean Small amnt to sediments

23 Carbonate shell formation the ocean s capacity to take up atmospheric CO 2 1. increases 2. decreases 82% 18% increases decreases

24 The Ultimate Inorg C Cycle CaSiO 3 + CO 2 CaCO 3 + SiO 2

25 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

26 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

27 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 million year timescale.

28 Is the silicate weathering volcanism InorgC cycle a positive or negative feedback? 1. Positive 2. Negative 58% 42% Positive Negative

29 Silicate Weathering Feedback Negative Feedback Stabilizing Climate - Initial Forcing + Silicate CO 2 Weathering Rate + + Temperature/ Precipitation

30 Does the silicate weathering feedback loop explain the glacial-interglacial cycling of atmospheric CO 2? 1. Yes 2. No 55% 45% Yes No

XI. the natural carbon cycle. with materials from J. Kasting (Penn State)

XI. the natural carbon cycle. with materials from J. Kasting (Penn State) XI. the natural carbon cycle with materials from J. Kasting (Penn State) outline properties of carbon the terrestrial biological cycle of carbon the ocean cycle of carbon carbon in the rock cycle overview