What can atmospheric 13 CO 2 tell us about the oceans and biosphere ? John B. Miller

1. What can atmospheric 13CO2 tell us about the oceans and biosphere? John B. Miller CIRES, University of Colorado, Boulder NOAA Climate Monitoring and Diagnostics Laboratory

2. Outline • What controls atmospheric 13CO2? • Global fluxes based on 13C. • Spatial breakdown of fluxes – what’s driving the global patterns? • Is the variability we see in the data really due to fluxes, or other terms in the budget?

3. Carbon Cycle Makes a Difference 2K difference From S. Denning

5. Global Sampling Network

6. δ13C data from Samoa Land Sink Land Source Land Sink Expected decrease due to Fossil Fuels (Relative) Rises in δ13C indicate a land sink for carbon, decreases indicate a source.

7. Discrimination Map(preference for 12C in photosynthesis – eL) Variations dominated by C3/C4 distribution. If not accounted for, C4 uptake looks like oceanic uptake, because of its small fractionation.

8. What is Disequilibrium? Residence time of carbon on land and in the oceans X Atm. History of δ13C Hard to estimate

10. Terrestrial Disequilibrium Based on atmospheric history and CASA model of respiration.

11. Oceanic Disequilibrium Annual Mean Based on measurements of DpCO2 and δ13C of DIC. Latitudinal gradient is caused by temperature dependent fractionation.

12. Now, Fluxes Red = Blue + Green

13. Global Partitioning (The Incredible Shrinking Ocean Sink) Pink=LeQuere ocean model with interannual variability in forcings. Black=Ocean model based on climatological forcings.

14. Onto Spatial Partitioning…Model Description • Relatively simple 2D model: 20 zonal bands; 10 vertical levels • Weak ‘rectifier effect’: 0.4 ppm • Reproduces observed SF6 meridional gradient using prescribed sources • Model not forced by prior guesses

15. Model Input: CO2 CO2 defined at every surface box in model domain.

16. Model Input: δ13C

17. Zonal Partitioning • Main Features • Width of bands is uncertainty. • Large Interannual Variability in the Tropics (maybe overestimated) • Sustained NH Land Sink • Sustained SH Ocean Sink • What was the biosphere doing in 96/97?

18. How does ENSO affect the Carbon Cycle? • ENSO affects both the tropical oceans and land. (no evidence for effects outside of tropics) • Strong El Nino to La Nina transitions

20. Zonal Partitioning

21. El Nino  La Nina pCO2

22. Zonal Partitioning

23. Sensitivity Analysis • Thick=control • Thin=Low C4 discriminatino • Thickdash=Larger Ocean diseq. • Dash=Larger Terrestrial diseq. • Main features are robust to our choice of discrimination and disequilibrium.

24. Alternative Explanation for Variations in Data

25. If the ocean model is right…then we can solve for disequilibrium 1. Red curve underestimates IAV, but still not enough to have Ocean flux constant. 2. Climatological OGCM would require an even steeper trend in disequilibrium. Inferred from ocean model and atm. data Red=Green + Blue Ocean: From ocean measurements Land: From biosphere model

26. Who’s Right? • What is more realistic: • 1. Shrinking and variable ocean sink? OR • 2. Rising and highly variable residence time of carbon in the land and oceans? • Either way 13C is telling us something intriguing!

27. Comparing Flux Estimates(Who’s Right II) All these methods have large (and hard to quantify) uncertainties

28. What’s Uncertain? • Disequilibrium: Interannual Variability and Land-use effects. • Productivity of C4 plants. • Mechanisms for terrestrial uptake and release (especially 1996 and 1997 anomalies)

29. Answers, orWhat’s Robust? • Temperate NH land sink very consistent, and LARGE • Temperate SH ocean sink very consistent • Large tropical land source in 97/98, followed by a large sink.