Interannual Variability in Carbon Sources and Sinks over North America: How Important Compared to Other Regions?

We study the variability of carbon sources and sinks over N. America in relation to other major land regions, using both forward modeling and atmospheric inversion results. Simulation for the 20th century shows a dominant ENSO mode over global land regions, and another mode related to global temperature trends. Large sub-continental scale variations in carbon sources and sinks over North America and Eurasia are comparable to those in the tropics, and the total interannual variability over North America is about 1 Pg y^-1. Such spatiotemporal variability has implication for flux measurement network distribution. We highlight the key differences in ENSO related climate anomalies and plant/soil physiology in determining the distintly different contributions between N. America/Eurasia and the tropics. Fire, largely driven by drought, also contributes significantly to the total flux at a rate of about 1 Pg y^-1 globally, and 0.5 Pg y^-1 for North America and Eurasia. The robust variability in tropical fluxes agree well with atmospheric inverse modeling results. Even over North America and Eurasia, where ENSO teleconnection is less robust, the fluxes show general agreement with inversion results, an encouraging sign for fruitful carbon data assimilation.