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

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NIR

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Models/Obs.

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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.