1. Lake Superior Region Carbon Cycle
Viewed from the air
Ankur R Desai
Atmospheric & Oceanic Sciences
University of Wisconsin-Madison
(and the CyCLeS team)
Lake Superior Biogeochemistry Workshop
August 5, 2008
Ankur R Desai, UW-Madison

2. What’s in the airwaves? Lakes, lands, & carbon
The atmospheric tracer view
An eddy flux view
Lake Superior & micrometerology
Ankur R Desai, UW-Madison

3. Lakes, Land, & Carbon
Ankur R Desai, UW-Madison

4. The big picture Sarmiento and Gruber, 2002, Physics Today
Ankur R Desai, UW-Madison

5. Slightly smaller picture
Cardille et al. (2007)
Ankur R Desai, UW-Madison

6. Real Numbers Are Complicated
Atmos. flux: ~3-12 Tg yr gC m-2 yr-1
Ankur R Desai, UW-Madison

7. An Oceanic Lake CyCLeS: Cycling of Carbon in Lake Superior
Adapt the MIT-GCM ocean model to simulate physical and biogeochemical environment of Lake Superior
Physical model of temperature, circulation
Mostly implemented
Biogeochemical model of trace nutrients and air-sea exchange
In progress
Ankur R Desai, UW-Madison

8. Interesting Questions
How do magnitudes of lake and land flux compare and what does it imply for regional carbon budgets? (NACP, SOCCR)
Are interannual variations in lake and land CO2 surface-atmosphere flux related and if so, due to what environmental forcing?
Can we “see” and constrain lake (and land) flux from regional atmospheric CO2 observations?
What are impacts on atmospheric forcing (temperature, stable layer depth, CO2) on lake biogeochemistry?
Ankur R Desai, UW-Madison

9. The Atmospheric Tracer View
Ankur R Desai, UW-Madison

10. Global CO2 NOAA/ESRL/GMD/CCGG Ankur R Desai, UW-Madison

11. Global Experiment Marland et al., DOE/CDIAC Ankur R Desai, UW-Madison

12. The Inverse Idea
Ankur R Desai, UW-Madison

13. The Inverse Idea Courtesy S. Denning, CSU Ankur R Desai, UW-Madison

14. The Inverse Idea Peters et al (2007) PNAS Ankur R Desai, UW-Madison

15. Inversion and a Very Big Tower
WLEF-TV (PBS)
Park Falls, WI
447-m tall
6 levels [CO2]
11 to 396 m
3 levels CO2 flux
30,122,396 m
Mixed landscape
Representative?
Running 1995-
Ankur R Desai, UW-Madison

16. A 1-point Inversion [CO2] Air flowing over lake > [CO2] over land
Ankur R Desai, UW-Madison

17. Air and Lake CO2 Comparison
Simple boundary layer budget tracer study suggests summer 2007 efflux: 4-14 gC m-2 d-1
extrapolated to ~ gC m-2 yr-1
Analysis requires modeling of stable marine boundary layer
Larger than traditional air-sea pCO2 exchange calculation
Requires significant respiration in water column
Urban et al. (in press)
Ankur R Desai, UW-Madison

18. The Boundary Layer Problem
Courtesy of S. Spak, UW
Ankur R Desai, UW-Madison

19. Getting More Sophisticated
Courtesy M. Uliasz, CSU
Tracer transport modeled influence function August 2003 at WLEF
entire domain
water
land
Ankur R Desai, UW-Madison

20. Great Lakes Influence at WLEF
Land: 85.4%
Lake Superior: 9.5%
Lake Michigan: 1.8%
Other water: 3.1%
Ankur R Desai, UW-Madison

21. The Potential
Potential exists for constraining flux and interannual var. with local observations of CO2
1996
2003
Ankur R Desai, UW-Madison

22. An Eddy Flux View
Ankur R Desai, UW-Madison

23. Eddies? Tracers in boundary layer primarily transported by turbulence
Ensemble average turbulent equations of motion and tracer concentration provide information about the effect of random, chaotic turbulence on the evolution of mean tracer profiles with time
In a quasi-steady, homogenous surface layer, we can simplify this equation to infer the surface flux of a tracer
Ankur R Desai, UW-Madison

24. Eddies!
Ankur R Desai, UW-Madison

25. The Maths *Some simplifications made… Storage Turbulent flux
Equipment:
3D sonic anemometer
Open or closed path gas analyzer
5--20 Hz temporal resolution
Multiple level CO2 profiler
Ankur R Desai, UW-Madison

26. The Data
Ankur R Desai, UW-Madison

27. The Data Pt. 2
Ankur R Desai, UW-Madison

28. The Data Pt. 3
Ankur R Desai, UW-Madison

29. Much Data…
Ankur R Desai, UW-Madison

30. A CHEAS-y Lake
Ankur R Desai, UW-Madison

31. Scale This!
Ankur R Desai, UW-Madison

32. Some Observations Desai et al, 2008, Ag For Met
Ankur R Desai, UW-Madison

33. The 6x6 km View
Ankur R Desai, UW-Madison

34. More Observations
Ankur R Desai, UW-Madison

35. Land History
Ankur R Desai, UW-Madison

36. Land History Have to account for age structure too
Ankur R Desai, UW-Madison

37. All The ChEAS Flux Data
Ankur R Desai, UW-Madison

38. Magically Scaled
Ankur R Desai, UW-Madison

39. The “Bottom-Up” Flux
Ankur R Desai, UW-Madison

40. Evaluation “Top-down” vs “Bottom-up” Ankur R Desai, UW-Madison

41. Evaluation
Ankur R Desai, UW-Madison

42. Land
average
Ankur R Desai, UW-Madison

43. Lake?
Ankur R Desai, UW-Madison

44. Lake and Land
Ankur R Desai, UW-Madison

45. Lake Superior & Micrometeorology
Ankur R Desai, UW-Madison

46. Better Forcing? Many observations are sparse Ankur R Desai, UW-Madison

47. Better [CO2]
Ankur R Desai, UW-Madison

48. Coherent Interannual Variability
Ankur R Desai, UW-Madison

49. Lake Interannual Variability
Annual avg. dissolved organic carbon (DOC)
Ankur R Desai, UW-Madison

50. More measurements [CO2] over Lake Superior
Continuous CO2 eddy covariance on the lake
Better models of stability over lakes
Spatial atmospheric met data
Temp, wind, precip?, shortwave radiation
Ankur R Desai, UW-Madison

51. Conclusions
On annual and decadal timescales, Lake Superior is possibly a source of CO2 to the atmosphere
This source could be on the same order of magnitude as the terrestrial regional sink
Regional carbon budgets have to take lakes into account
We can estimate this flux from a number of techniques
Lake models may need to worry about spatiotemporal variability in atmospheric forcing
Models to tie land carbon flows into lake carbon can be useful for Lake Superior
Model-data fusion/optimization/assimilation techniques should be explored
Ankur R Desai, UW-Madison

52. Thanks
Desai lab and friends: Ben Sulman, Jonathan Thom, Shelley Knuth, Scott Spak
ChEAS collaborators, esp. Bruce Cook, Paul Bolstad, Ken Davis, D. Scott Mackay, Nic Saliendra, Sudeep Samanta
CyCLeS team: Galen McKinley, Noel Urban, Chin Wu, Nazan Atilla, Val Bennington
Funding: DOE NICCR, NSF, USDA, NSF/NCAR, NASA, NOAA, under auspices of the North American Carbon Program (NACP)
Come visit us:
AOSS 1549,
More info:
Ankur R Desai, UW-Madison