Greenhouse gas fluxes from Alaska's North Slope inferred from the Airborne Carbon Measurements campaign (ACME-V)

Abstract

Northern high latitudes are likely to be heavily impacted by climate change, changes that will undoubtedly alter carbon cycling across these regions. An understanding of both the magnitude and drivers of current CO2 and CH4 fluxes are a prerequisite for making robust projections of future changes. In this study, we use observations from the recent Airborne Carbon Measurements (ACME-V) aircraft campaign to estimate the magnitude and environmental predictors CO2 and CH4 fluxes in Alaska. ACME-V consisted of 38 flights across the North Slope between late May and mid-September 2015, making it the most detailed airborne survey of northern Alaska to date. These data, combined with a geostatistical inverse model, provide a unique lens into fluxes across the region. Using this approach, we estimate a large CO2 flux to the atmosphere from the North Slope of Alaska in early summer that is counterbalanced by CO2 uptake in late summer; this balance between early season respiration and late-summer photosynthesis drives the total summer CO2 flux across northern Alaska during the study period. We further compare our results to process-based flux estimates (the Terrestrial Model Intercomparison Project, MsTMIP and the Wetland and Wetland CH4 Inter-comparison of Models Project, WETCHIMP) and several recent studies of the same spatial domain. We observe a similarity in CO2 flux totals between MsTMIP suite of models and our study (June 2015–0.86 – 0.57 vs 0.96, July 2015 MsTMIP −1.01 – 0.00 vs −0.14 and August 2915 MsTMIP −0.73 – 0.29 vs −0.50 μmol m−2 s−1, MsTMIP and our study, respectively, averaged across the North Slope). However, we find significantly higher CH4 fluxes from the North Slope than any of the WETCHIMP models. Specifically, we estimate total CH4 fluxes from the North Slope of Alaska of +0.64 ± 0.13 Tg (95% confidence), during June through August 2015 while the WETCHIMP model estimates range from 0.004 to 0.1 Tg, depending upon the model. Furthermore, the contribution of the North Slope tundra to the overall Alaskan CH4 fluxes during the entire period was ~27%, compared to 3% in state-of-the-art process-based models.