Interannual variability of the global carbon cycle (1992-2005) inferred by inversion of atmospheric CO2 and δ13CO2 measurements

We present estimates of the surface sources and sinks of CO2 for 1992 - 2005 deduced from atmospheric inversions. We use atmospheric CO2 records from 67 sites and 10 delta(CO2)-C-13 records. We use two atmospheric models to increase the robustness of the results. The results suggest that interannual variability is dominated by the tropical land. Statistically significant variability in the tropical Pacific supports recent ocean modeling studies in that region. The northern land also shows significant variability. In particular, there is a large positive anomaly in 2003 in north Asia, which we associate with anomalous biomass burning. Results using delta(CO2)-C-13 and CO2 are statistically consistent with those using only CO2, suggesting that it is valid to use both types of data together. An objective analysis of residuals suggests that our treatment of uncertainties in CO2 is conservative, while those for delta(CO2)-C-13 are optimistic, highlighting problems in our simple isotope model. Finally, delta(CO2)-C-13 measurements offer a good constraint to nearby land regions, suggesting an ongoing value in these measurements for studies of interannual variability.