Impact of Fraserdale CO₂ observations on annual flux inversion of the North American boreal region

In TransCom-3 (Level 1), atmospheric CO₂ measurements from 76 monitoring stations for the period 1992-1996 and 16 atmospheric transport models were used to constrain annual mean CO₂ fluxes over 11 land and 11 ocean regions. The tower measurements of atmospheric CO₂ from Fraserdale, a continental site in northern Ontario, Canada are now available and processed for use in the TransCom-3 inverse modelling framework. In this short study, we show that by including this set of continental CO₂ data, the estimated flux for the North American boreal region becomes nearly zero, a reduction of about 0.26 Pg C yr^-1 from the previous estimate. The uncertainty of the estimated flux for this region is also reduced by ∼30%. All transport models show negative changes for boreal North America, with the strongest responses (∼ -0.5 Pg C yr^-1) shown by NIRE, NIES, CSU and SKYHI. Furthermore, models showing a strong response in boreal North America tend to show strong sensitivity in middle- and high-latitude Asian regions.