1. ATOC 220 The Contemporary Global Carbon Cycle The contemporary record of atmospheric CO 2 –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 CO 2 Professor NT Roulet, November 20, 2006

2. Seasonal fluctuation in atmospheric CO 2 (at Mauna Loa, Hawaii)

3. Black: pre-industrial Red: + industrial era up to ~1990 Sedimentary rock 40,000,000 (CaCO 3 ) (IPCC, 2006) Global Carbon Cycle

4. 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 inflowoutflow = reservoir volume

5. Carbon storage & transfer in a terrestrial ecosystem Atmosphere Primary producers Consumers Dead organic matter Soil

6. Atmospheric CO 2 590 (751) Gt C Outflow: 60 Gt C/yr Inflow: 60 Gt C/yr Respiration & decomposition Photosynthesis C exchange between atmosphere & terrestrial plants 600 Gt C 1700 Gt C

7. Atmospheric CO 2 590 (751) Gt C 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

8. Rondonia (Amazon) 1975 1986 1992

9. 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 0.68  0.34 Gt C/yr. http://cybele.bu.edu/greening earth/ge.html

10. Step 1 convert absorbed radiation to optimal gross production Step 2 downgrade by climate limiting factors to obtain gpp Step 3 subtract 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

11. 1. The marine biological pump Deep Ocean Ocean surface atmospheric CO 2 Phytoplankton sedimentation of organic C Bacterial decomposition CO 2 Nutrients upwelling

12. 2. The solubility pump Ocean surface Atmosphere H 2 CO 3  H + + HCO 3 - HCO 3 -  H + + CO 3 2- CO 2 CO 2 + H 2 O  H 2 CO 3 bicarbonate carbonate carbonic acid

13. CO 2 (aq) dissociates rapidly into DIC while increasing acidity: pH  K 1 K 2 CO 2 + H 2 O  HCO 3 - + H +  CO 3 2- + 2H + Bjerrum Plot: pH = 8.1 T = 25 0 C, S = 35 [CO 2 ] : [HCO 3 - ] : [CO 3 = ]  0.5% : 86.5% : 13% (Zeebe & Wolf-Gladrow, 2002) bicarbonatecarbonate

14. Ocean surface Atmosphere H 2 CO 3  H + + HCO 3 - CO 2 CO 2 + H 2 O  H 2 CO 3 Ca 2+ + 2HCO 3 -  CaCO 3 + H 2 CO 3 shelled organisms The solubility pump & calcium carbonate formation

15. Ca 2+ + 2HCO 3 -  CaCO 3 + H 2 CO 3 rock weathering solubility pump shelled organisms Sediments

16. Foraminiferans (Protozoa) <0.5 mm in size. live in the plankton & in the sediments. feed on bacteria. produce ~1 billion tons of CaCO 3 per yr.

17. Coccolithophores (algae) planktonic produce 1.5 million tons of CaCO 3 per yr sometimes form “blooms” at the ocean surface which reflect visible light SeaWiFS image 16 July 2000

18. Atmospheric CO 2 590 (751) Gt C Outflow: 70 (20) Gt C/yr Inflow: 70 (22) Gt C/yr Gas exchange C exchange between atmosphere & the ocean 3 Gt C 900 Gt C

19. Atmospheric CO 2 590 (751) Gt C 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 C 900 Gt C 90 Gt C/yr 11 Gt C/yr 101 Gt C/yr

20. Atmospheric CO 2 590 (751) Gt C 70 (90) Gt C/yr C exchange between atmosphere & the ocean 3 Gt C 900 Gt C 90 Gt C/yr 11 Gt C/yr 101 Gt C/yr One more issue How can you have more organic C export than exists in living biomass?

21. 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 NPP g C/m 2 /yr

22. 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