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Main Concepts
Current CO2 levels: fluxes in and outWhat are C reservoirs?
Natural CO2 sources and sinks:The land breathes.The ocean breathes.The rocks breathe.
Carbon Residence time?Timescales of carbon removal from the
atmosphere.
Atmospheric CO2
What are the major sources of C emissions? How unique are modern CO2 levels? Where does it all go?How long will it stick around?
Estimating Ancient CO2:Leaf Stomata
Stomata density related to CO2
high CO2 = low stomatal density
Living
Fossil
Carbon fluxes (in Gt/yr), reservoirs (bold, Gt), and residence times (years)
Note: 2006 emissions were 7.7 Gt / year,
as of 1990
How much is a gigaton (Gt)?
• One billion metric tons (1015 g)
• It is about 2750 Empire State Buildings.
• Global C emissions are about 6 Gt.
Carbon cycle fluxesThese have significant errors and change year-to-year
Cycling Flux rate (Gt/year)
Ocean uptake -2.0
Photosynthesis -120.0
Respiration +120.0
Fossil Fuel Combustion
+6.0
Biomass burning +1.0
( “-” means removed from atmosphere; 1990 data)
Carbon “sinks”
Source:
Carbon Emissions: 6.0 Gt/year
Sink:
Obs. Atm increase: 3.2 Gt/year
Ocean uptake: 2.0 Gt/year
“missing sink”: 1.8 Gt/year1990 estimates
Air-Sea CO2 fluxes
Ocean uptake
Ocean release
Gases are more soluble in COLD water
Ocean uptake
Ocean uptake Ocean release
Net:-2 Gt/yr
Ocean and Atmoshere C reservoirs
Ocean C: 39,000 Gt (as HCO3-, CO3
2-)
Atmosphere: 1580 Gt (as CO2)
Ocean has 50x more carbon than the atmosphere.
Calculating Residence time
Residence time is a “replacement time”: time required to affect a reservoir given a certain flux.
(years) = reservoir / input rate
Example: Residence time of a CU undergradReservoir: Size of Columbia’s UG Student
Body?Input rate: Incoming 1st-year class size
Calculating residence time of Carbon due to air-sea exchange
Ocean uptake rate: -2.0 Gt / year
Total Ocean C reservoir : 39,000 Gt
Surface Ocean C reservoir : 600 Gt
C residence time (whole ocean) = ?
C residence time (surface only) = ?
Carbon Cycle Budget
At steady state: Sources = Sinks
Sources: Respiration, FF, land useSinks: Photosynthesis, ocean uptake
But.. C is not at steady state… (CO2 is rising, right? Equivalent to +3.2 x1015g/ year
So the following should be true:+3.2 Gt/year = (Sources) + (Sinks)
The missing C sink (Gt/yr)
+3.2 = (Sources) + (Sinks) + (other)
+3.2 = (122+90+6+1) + (-120-92-2) + (other)+3.2 = (219 - 214) + (other)“other” = 5.0 - 3.2
“other” = missing sink of -1.8 Gt/year
This “missing sink” has been removing C from atmosphere each year…(a good thing)
Missing C sink: What is it?
CO2 fertilization of high-latitude forests
Plants grow faster/better at higher CO2
Atm CO2 level
Plant Cuptake
Current state of the Missing Sink
“Missing sink” was accelerated growth of northern forests under high CO2 (carbon uptake)
This sink is now completely offset by tropical deforestation. (additional carbon emission)
Bolivia (1984-1998)
The future of fossil fuel CO2
How quickly would the planet take up our CO2?
Fast: “solubility pump” Air-Sea CO2 exchange (centuries)
Moderate: “Deep ocean acid neutralization” (tens of thousands of years)
Really slow: “Weathering of continental rocks” (millions of years)
Really Slow C cycling
Continental weathering (dissolves mountains!)“Urey reaction” - millions of yearsCaSiO3 + CO2 --> CaCO3 + SiO2
Carbon Reservoirs (1Gt = 1015g)
Reservoir Size
Rocks 65,000,000
Oceans 39,000
Soils 1,580
Land Plants 610