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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

desai@aos.wisc.edu

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

desai@aos.wisc.edu

lakes land carbon
Lakes, Land, & Carbon

desai@aos.wisc.edu

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

desai@aos.wisc.edu

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

desai@aos.wisc.edu

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

desai@aos.wisc.edu

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

desai@aos.wisc.edu

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?

desai@aos.wisc.edu

the atmospheric tracer view
The Atmospheric Tracer View

desai@aos.wisc.edu

global co 2
Global CO2
  • NOAA/ESRL/GMD/CCGG

desai@aos.wisc.edu

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

desai@aos.wisc.edu

the inverse idea
The Inverse Idea

desai@aos.wisc.edu

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

desai@aos.wisc.edu

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

desai@aos.wisc.edu

inversion and a very big tower
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-

desai@aos.wisc.edu

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

desai@aos.wisc.edu

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)

desai@aos.wisc.edu

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

desai@aos.wisc.edu

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

entire domain

water

land

desai@aos.wisc.edu

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%

desai@aos.wisc.edu

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

1996

2003

desai@aos.wisc.edu

an eddy flux view
An Eddy Flux View

desai@aos.wisc.edu

eddies
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

desai@aos.wisc.edu

eddies24
Eddies!

desai@aos.wisc.edu

the maths
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

desai@aos.wisc.edu

the data
The Data

desai@aos.wisc.edu

the data pt 2
The Data Pt. 2

desai@aos.wisc.edu

the data pt 3
The Data Pt. 3

desai@aos.wisc.edu

much data
Much Data…

desai@aos.wisc.edu

a cheas y lake
A CHEAS-y Lake

desai@aos.wisc.edu

scale this
Scale This!

desai@aos.wisc.edu

some observations
Some Observations

Desai et al, 2008, Ag For Met

desai@aos.wisc.edu

the 6x6 km view
The 6x6 km View

desai@aos.wisc.edu

more observations
More Observations

desai@aos.wisc.edu

land history
Land History

desai@aos.wisc.edu

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

desai@aos.wisc.edu

all the cheas flux data
All The ChEAS Flux Data

desai@aos.wisc.edu

magically scaled
Magically Scaled

desai@aos.wisc.edu

the bottom up flux
The “Bottom-Up” Flux

desai@aos.wisc.edu

evaluation
Evaluation
  • “Top-down” vs “Bottom-up”

desai@aos.wisc.edu

evaluation41
Evaluation

desai@aos.wisc.edu

slide42
Land
  • 1989-2006 average

desai@aos.wisc.edu

slide43
Lake?

desai@aos.wisc.edu

lake and land
Lake and Land

desai@aos.wisc.edu

better forcing
Better Forcing?
  • Many observations are sparse

desai@aos.wisc.edu

better co 2
Better [CO2]

desai@aos.wisc.edu

lake interannual variability
Lake Interannual Variability

Annual avg. dissolved organic carbon (DOC)

desai@aos.wisc.edu

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

desai@aos.wisc.edu

conclusions
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

desai@aos.wisc.edu

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

desai@aos.wisc.edu