Patterns of CO 2 and radiocarbon across high northern latitudes during International Polar Year 2008

High‐resolution in situ CO 2 measurements were conducted aboard the NASA DC‐8 aircraft during the ARCTAS/POLARCAT field campaign, a component of the wider 2007–2008 International Polar Year activities. Data were recorded during large‐scale surveys spanning the North American sub‐Arctic to the North Pole from 0.04 to 12 km altitude in spring and summer of 2008. Influences on the observed CO 2 concentrations were investigated using coincident CO, black carbon, CH 3 CN, HCN, O 3 , C 2 Cl 4 , and Δ 14 CO 2 data, and the FLEXPART model. In spring, the CO 2 spatial distribution from 55°N to 90°N was largely determined by the long‐range transport of air masses laden with Asian anthropogenic pollution intermingled with Eurasian fire emissions evidenced by the greater variability in the mid‐to‐upper troposphere. At the receptor site, the enhancement ratios of CO 2 to CO in pollution plumes ranged from 27 to 80 ppmv ppmv −1 with the highest anthropogenic content registered in plumes sampled poleward of 80°N. In summer, the CO 2 signal largely reflected emissions from lightning‐ignited wildfires within the boreal forests of northern Saskatchewan juxtaposed with uptake by the terrestrial biosphere. Measurements within fresh fire plumes yielded CO 2 to CO emission ratios of 4 to 16 ppmv ppmv −1 and a mean CO 2 emission factor of 1698 ± 280 g kg −1 dry matter. From the 14 C in CO 2 content of 48 whole air samples, mean spring (46.6 ± 4.4‰) and summer (51.5 ± 5‰) Δ 14 CO 2 values indicate a 5‰ seasonal difference. Although the northern midlatitudes were identified as the emissions source regions for the majority of the spring samples, depleted Δ 14 CO 2 values were observed in <1% of the data set. Rather, ARCTAS Δ 14 CO 2 observations (54%) revealed predominately a pattern of positive disequilibrium (1–7‰) with respect to background regardless of season owing to both heterotrophic respiration and fire‐induced combustion of biomass. Anomalously enriched Δ 14 CO 2 values (101–262‰) measured in emissions from Lake Athabasca and Eurasian fires speak to biomass burning as an increasingly important contributor to the mass excess in Δ 14 CO 2 observations in a warming Arctic, representing an additional source of uncertainty in the quantification of fossil fuel CO 2 .