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Testing the consistency of T3L2 Cyclo-stationary fluxes
with 13C observations
John Miller1, Scott Denning2, Neil Suits2, Kevin Gurney2, Jim White3
and T3 Modelers
1. NOAA/CMDL2. CSU3. CU/INSTAAR
Outline
1. Comparison of simulated and observed 13C: seasonal cycles and annual mean latitudinal gradient.
2. Sensitivity tests: a)Fractionation b)Disequilibrium c)CO2 flux – Are differences in ‘1’ meaningful?
3. Shifting flux between land and sea.4. Across model differences
δ13C from Samoa:the signal is in the data!
Land Source
Land Sink
Land Sink
Expected decrease due to Fossil Fuels
(Relative) Rises in δ13C indicate a land sink for carbon, decreases indicate a source.
Overview of Method
1. Take CO2 fluxes derived from mean seasonal cycle inversion.
2. Multiply fluxes by isotopic signatures and add fossil fuel and disequilibrium ‘iso-fluxes’
3. ‘Multiply’ iso-fluxes by response functions to get predicted isotopic ratios
4. Compare simulated δ13C to observed.
Source of Inputs
1. Fluxes T3L22. Discrimination SiB2(.5)
aggregated to T3 regions3. Land disequilibrium CASA model
RH
4. Ocean disequilibrium Keeling 13C of DIC, Takahashi pCO2
5. Single value for ff
Posterior CO2 v. ‘Observed’ --NIES model
(good…)Amplitudes
Posterior CO2 v. ‘Observed’(… but not everywhere)
Posterior CO2 v. Observed
Simulated and Observed δ13C
Simulated and Observed δ13C
Simulated and Observed δ13C
Sensitivity to Discrimination
Sensitivity to Discrimination
Sensitivity to Discrimination
Sensitivity to Flux Error
1.In each month, take 0.5 sigma posterior uncertainty from Temperate N. American land flux and either a) add this to the land or the ocean (subtracting the same from the complimentary region, to conserve flux.
2.This answers the question of whether the isotopic mismatch simply falls within the already determined uncertainty in the retrieved fluxes.
Sensitivity to Flux Error
Sensitivity to Flux Error
Sensitivity to Disequilibrium Error
Sensitivity to Disequilibrium Error
What does this tell us?
1. Shallow gradient and small seaonality.
2. Mismatches may be partially due to incorrect specification of discrimination, but not wholly.
3. Not a function of disequilibrium or flux uncertainty.
4. What’s left is the fluxes themselves! So, we can try moving around fluxes to see if we can match the data.
Now, shift ~2 Pg uptake from Ocean to Land during summer
However…
We can restore the lat. grad. by dramatically altering
disequilibrium
Across Model Summary
Lat. Grad. Comparison
-0.0014
-0.0012
-0.001
-0.0008
-0.0006
-0.0004
-0.0002
0
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ions
CS
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TM
UC
B
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JMA
M.C
CM
3
M.N
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P
M.M
AC
CM
2
NIE
S
NIR
E
TM
2
TM
3
Models/Obs.
per
mil
/deg
. la
t
Series1
Conclusions
1. 13C observations can improve our flux determination, especially where ‘leakage’ may exist.
2. Seasonal cycle amplitude and latitudinal gradient seem to be largely independent parameters
3. This means that we can solve for both fluxes and improved estimates of disequilibrium and thus land and ocean parameters.