Testing the consistency of T3L2 Cyclo-stationary fluxes with  13 C observations John Miller 1, Scott Denning 2, Neil Suits 2, Kevin Gurney 2, Jim White 3 and T3 Modelers 1.NOAA/CMDL 2.CSU 3.CU/INSTAAR

Outline 1.Comparison of simulated and observed  13 C: seasonal cycles and annual mean latitudinal gradient. 2.Sensitivity tests: a)Fractionation b)Disequilibrium c)CO 2 flux – Are differences in ‘1’ meaningful? 3.Shifting flux between land and sea. 4.Across model differences

δ 13 C from Samoa: the signal is in the data! Land Source Land Sink Expected decrease due to Fossil Fuels (Relative) Rises in δ 13 C indicate a land sink for carbon, decreases indicate a source.

Overview of Method 1.Take CO 2 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 δ 13 C to observed.

Source of Inputs 1.Fluxes  T3L2 2.Discrimination  SiB2(.5) aggregated to T3 regions 3.Land disequilibrium  CASA model R H 4.Ocean disequilibrium  Keeling  13 C of DIC, Takahashi pCO 2 5.Single value for  ff

Posterior CO 2 v. ‘Observed’ --NIES model (good…) Amplitudes

Posterior CO 2 v. ‘Observed’ (… but not everywhere)

Posterior CO 2 v. Observed

Simulated and Observed δ 13 C

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 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

Conclusions  13 C 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.