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 pm

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

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 years 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 Tundra Forest Grassland Temperature 0oC0oC Precipitation Desert

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

Atmospheric CO 2 Seasonal Cycle Atmosphere responds to biosphere on short timescales

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

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

The effect of deforestation on atmospheric CO 2 is 1.to increase it (source) 2.to decrease it (sink) 3.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

Marine Organic C Cycle death/fecal matter OrgC sinks OrgC and nutrients Surface Ocean Deeper Ocean CO 2(aq) + nutrients Photosynthesis CO 2(aq) O2O2 a tiny bit to sediments CO 2 decay

Biological OrgC Pump: Key Points CO 2 and nutrients pumped down by biota Thermo-Haline Circulation 1. Surface depleted (relatively) in C and nutrients 2. Deep ocean enriched in C and nutrients 3. Atmospheric CO 2 responds to net pumping Surface Ocean Deeper Ocean ~1000 yrs 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 Ocean 3.7x10 4 Gtons Lithosphere 4x10 7 Gtons Mainly as CO 2 Mainly as HCO 3 - Mainly as CaCO 3 Carbon in the oceans is mostly in an inorganic form

Shell Formation Surface Ocean Deep Ocean CO Ca 2+ Shell formation (CaCO 3(s) ) death/shells sink CaCO 3(s) DIC slow Slow THC Small amnt to sediments

Carbonate shell formation ___________ the ocean’s capacity to take up atmospheric CO 2 1.increases 2.decreases

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

Silicate Weathering CaSiO 3 + CO 2  CaCO 3 + SiO 2 CaSiO 3 Rock CO 2 (atm) CaSiO 3 Rock CaCO 3 + SiO 2 Oceans Ca 2+ CO 3 2- SiO 2 Rain/runoff Chemical Weathering Rate  Faster with higher CO 2, higher T, higher rainfall

Volcanic Degassing Volcanism causes reverse of weathering 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 HEAT

Silicate Weathering “Thermostat” CO 2 CaSiO 3  CaCO 3 + SiO 2 Precip/runoff Chemical weathering 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

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

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