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