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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. What’s in the airwaves?. Lakes, lands, & carbon The atmospheric tracer view

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lake superior region carbon cycle

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

what s in the airwaves
What’s in the airwaves?
  • Lakes, lands, & carbon
  • The atmospheric tracer view
  • An eddy flux view
  • Lake Superior & micrometerology

lakes land carbon
Lakes, Land, & Carbon

the big picture
The big picture
  • Sarmiento and Gruber, 2002, Physics Today

slightly smaller picture
Slightly smaller picture
  • Cardille et al. (2007)

real numbers are complicated
Real Numbers Are Complicated
  • Atmos. flux: ~3-12 Tg yr-1 - 35-140 gC m-2 yr-1

an oceanic lake
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

interesting questions
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?

the atmospheric tracer view
The Atmospheric Tracer View

global co 2
Global CO2

global experiment
Global Experiment
  • Marland et al., DOE/CDIAC

the inverse idea
The Inverse Idea

the inverse idea13
The Inverse Idea
  • Courtesy S. Denning, CSU

the inverse idea14
The Inverse Idea
  • Peters et al (2007) PNAS

inversion and a very big tower
Inversion and a Very Big Tower
  • 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-

a 1 point inversion
A 1-point Inversion
  • [CO2] Air flowing over lake > [CO2] over land

air and lake co 2 comparison
Air and Lake CO2 Comparison
  • 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)

the boundary layer problem
The Boundary Layer Problem
  • Courtesy of S. Spak, UW

getting more sophisticated
Getting More Sophisticated
  • Courtesy M. Uliasz, CSU
    • Tracer transport modeled influence function August 2003 at WLEF

entire domain



great lakes influence at wlef
Great Lakes Influence at WLEF
  • Land: 85.4%
  • Lake Superior: 9.5%
  • Lake Michigan: 1.8%
  • Other water: 3.1%

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



an eddy flux view
An Eddy Flux View

  • 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


the maths
The Maths
  • *Some simplifications made…


Turbulent flux

  • Equipment:
  • 3D sonic anemometer
  • Open or closed path gas analyzer
  • 5--20 Hz temporal resolution
  • Multiple level CO2 profiler

the data
The Data

the data pt 2
The Data Pt. 2

the data pt 3
The Data Pt. 3

much data
Much Data…

a cheas y lake
A CHEAS-y Lake

scale this
Scale This!

some observations
Some Observations

Desai et al, 2008, Ag For Met

the 6x6 km view
The 6x6 km View

more observations
More Observations

land history
Land History

land history36
Land History
  • Have to account for age structure too

all the cheas flux data
All The ChEAS Flux Data

magically scaled
Magically Scaled

the bottom up flux
The “Bottom-Up” Flux

  • “Top-down” vs “Bottom-up”


  • 1989-2006 average


lake and land
Lake and Land

better forcing
Better Forcing?
  • Many observations are sparse

better co 2
Better [CO2]

lake interannual variability
Lake Interannual Variability

Annual avg. dissolved organic carbon (DOC)

more measurements
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

  • 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 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,, 265-9201
  • More info: