ATOC 220 The Contemporary Global Carbon Cycle
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Transcript of ATOC 220 The Contemporary Global Carbon Cycle
ATOC 220The Contemporary
Global Carbon Cycle
• The contemporary record of atmospheric CO2– The best ‘known’, ‘beautiful’ and ‘most
disturbing’ graphs in all of geoscience• Overall C cycle
– Terrestrial component of the C cycle– Ocean component of the C cycle
• Putting it all together to explain the contemporary record of change in atmospheric CO2
Professor NT Roulet, November 20, 2006
Seasonal fluctuation in atmospheric CO2
(at Mauna Loa, Hawaii)
Black: pre-industrial Red: + industrial era up to ~1990
Sedimentary rock40,000,000 (CaCO3)
(IPCC, 2006)
Global Carbon Cycle
• C is stored in different reservoirs and is exchanged between these reservoirs.
• Material enters & leaves at certain rates.
• Material remains in a reservoir temporarily.
Residence time of material
Reservoir volume (at steady state) flow rate
inflow outflow
=
reservoir volume
Carbon storage & transfer in a terrestrial ecosystem
Atmosphere
Primaryproducers
Consumers
Deadorganic matter
Soil
Atmospheric CO2
590 (751) Gt COutflow:60 Gt C/yr
Inflow:60 Gt C/yr
Respiration &decomposition
Photosynthesis
C exchange between atmosphere & terrestrial plants
600 Gt C1700 Gt C
AtmosphericCO2
590 (751) Gt C
60 Gt C/yr 60 Gt C/yr
C exchange between atmosphere & the terrestrial biosphere
Residence time of C in terrestrial biosphere
reservoir size flow rate
600 (2300) Gt 60 Gt/yr
=
=10 (38) yrs
Live terrestrial C has a residence time of ~10 yrs (total terrestrial C ~ 40 yrs)
600 Gt C
1700 Gt C
Rondonia (Amazon)
1975
1986
1992
Forest Regrowth
Pool changes were evaluated as the difference between the late 1990s and early 1980s pool estimates, pixel-by-pixel, and quoted on a per year basis.The carbon pool in the woody biomass of northern forests (1.5 billion ha) is estimated to be 61 20 Gt C during the late 1990s.
Our sink estimate for the woody biomass during the 1980s and 1990s is 0.680.34 Gt C/yr.http://cybele.bu.edu/greeningearth/ge.html
Step 1convert absorbed radiation to optimal gross production
Step 2downgrade by climate limiting
factors to obtain gpp
Step 3subtract respiration to obtain npp
Average of interannual trends (1982-99) in growing season NPP estimated with GIMMS and PAL (v3) FPAR
Trends in NPP are positive over 55% of the global vegetated area and are statistically more significant than the declining trends
observed over 19% of the vegetated area.
The NPP Algorithm
http://cybele.bu.edu/greeningearth/ge.html
1. The marine biological pump
Deep Ocean
Ocean surface
atmospheric CO2
Phytoplankton
sedimentationof organic C
BacterialdecompositionCO2
Nutrients
upwelling
2. The solubility pump
Ocean surfaceAtmosphere
H2CO3 H+ + HCO3-
HCO3- H+ + CO3
2-
CO2
CO2 + H2O H2CO3
bicarbonate
carbonate
carbonic acid
CO2(aq) dissociates rapidly into DIC while increasing acidity: pH
K1 K2
CO2 + H2O HCO3- + H+ CO3
2- + 2H+
Bjerrum Plot:pH = 8.1
T = 250C, S = 35 [CO2] : [HCO3
-] : [CO3=]
0.5% : 86.5% : 13%
(Zeebe & Wolf-Gladrow, 2002)
bicarbonate carbonate
Ocean surfaceAtmosphere
H2CO3 H+ + HCO3-
CO2
CO2 + H2O H2CO3
Ca2+ + 2HCO3- CaCO3 + H2CO3
shelled organisms
The solubility pump &calcium carbonate formation
Ca2+ + 2HCO3- CaCO3 + H2CO3
rockweathering
solubilitypump
shelled organisms
Sediments
Foraminiferans (Protozoa)
• <0.5 mm in size.
• live in the plankton & in the sediments.
• feed on bacteria.
• produce ~1 billion tons of CaCO3 per yr.
Coccolithophores (algae)• planktonic• produce 1.5 million tons of CaCO3 per yr• sometimes form “blooms” at the ocean surface which reflect visible light
SeaWiFS image 16 July 2000
Atmospheric CO2
590 (751) Gt C
Outflow:70 (20) Gt C/yr
Inflow:70 (22) Gt C/yr
Gas exchange Gas exchange
C exchange between atmosphere & the ocean
3 Gt C
900 Gt C
AtmosphericCO2
590 (751) Gt C
70 (90) Gt C/yr 70 (90) Gt C/yr
C exchange between atmosphere & the ocean
Residence time of C in surface ocean
reservoir size flow rate
900 Gt 170 (190) Gt/yr
=
=5 (4.7) yrs
3 Gt C900 Gt C
90 Gt C/yr
11 Gt C/yr101 Gt C/yr
AtmosphericCO2
590 (751) Gt C
70 (90) Gt C/yr 70 (90) Gt C/yr
C exchange between atmosphere & the ocean
3 Gt C900 Gt C
90 Gt C/yr
11 Gt C/yr101 Gt C/yr
One more issue
How can you have more organic C export than exists in living biomass?
Ocean net primary production
Global Ocean NPP ~ 50 to 60 Gt C/yr
Therefore if the living biomass is 3 Gt C it means the residence time of the plankton < a few weeks
NP
P g
C/m
2 /yr
Pulling this all together
• Terrestrial system exchanging ~ 60 Gt C/yr with the atmosphere but with a definite seasonality
• Ocean system exchanging ~ 90 Gt C/yr with the atmosphere of ocean NPP forms part of the uptake and solubility the rest