Lake Superior Region Carbon Cycle - PowerPoint PPT Presentation

Lake Superior Region Carbon Cycle

Ankur R Desai

Atmospheric & Oceanic Sciences

University of Wisconsin-Madison

(and the CyCLeS team)

Viewed from the air

Lake Superior Biogeochemistry Workshop

August 5, 2008

desai@aos.wisc.edu

• Lakes, lands, & carbon
• The atmospheric tracer view
• An eddy flux view
• Lake Superior & micrometerology

desai@aos.wisc.edu

desai@aos.wisc.edu

• Sarmiento and Gruber, 2002, Physics Today

desai@aos.wisc.edu

• Cardille et al. (2007)

desai@aos.wisc.edu

• Atmos. flux: ~3-12 Tg yr-1 - 35-140 gC m-2 yr-1

desai@aos.wisc.edu

• 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

desai@aos.wisc.edu

• 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?

desai@aos.wisc.edu

desai@aos.wisc.edu

• NOAA/ESRL/GMD/CCGG

desai@aos.wisc.edu

• Marland et al., DOE/CDIAC

desai@aos.wisc.edu

desai@aos.wisc.edu

• Courtesy S. Denning, CSU

desai@aos.wisc.edu

• Peters et al (2007) PNAS

desai@aos.wisc.edu

• 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-

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• [CO2] Air flowing over lake > [CO2] over land

desai@aos.wisc.edu

• Simple boundary layer budget tracer study suggests summer 2007 efflux: 4-14 gC m-2 d-1
• extrapolated to ~30-140 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)

desai@aos.wisc.edu

• Courtesy of S. Spak, UW

desai@aos.wisc.edu

• Courtesy M. Uliasz, CSU
• Tracer transport modeled influence function August 2003 at WLEF

entire domain

water

land

desai@aos.wisc.edu

• Land: 85.4%
• Lake Superior: 9.5%
• Lake Michigan: 1.8%
• Other water: 3.1%

desai@aos.wisc.edu

• Potential exists for constraining flux and interannual var. with local observations of CO2

1996

2003

desai@aos.wisc.edu

desai@aos.wisc.edu

• 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

desai@aos.wisc.edu

desai@aos.wisc.edu

• *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

desai@aos.wisc.edu

desai@aos.wisc.edu

desai@aos.wisc.edu

desai@aos.wisc.edu

desai@aos.wisc.edu

desai@aos.wisc.edu

desai@aos.wisc.edu

Desai et al, 2008, Ag For Met

desai@aos.wisc.edu

desai@aos.wisc.edu

desai@aos.wisc.edu

desai@aos.wisc.edu

• Have to account for age structure too

desai@aos.wisc.edu

desai@aos.wisc.edu

desai@aos.wisc.edu

desai@aos.wisc.edu

• “Top-down” vs “Bottom-up”

desai@aos.wisc.edu

desai@aos.wisc.edu

• 1989-2006 average

desai@aos.wisc.edu

desai@aos.wisc.edu

desai@aos.wisc.edu

desai@aos.wisc.edu

• Many observations are sparse

desai@aos.wisc.edu

desai@aos.wisc.edu

desai@aos.wisc.edu

Annual avg. dissolved organic carbon (DOC)

desai@aos.wisc.edu

• [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

desai@aos.wisc.edu

• 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

desai@aos.wisc.edu

• 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, desai@aos.wisc.edu, 265-9201
• More info:
• http://flux.aos.wisc.edu

desai@aos.wisc.edu