Sigrid Dengel https://orcid.org/0000-0002-4774-9188
Dave Billesbach https://orcid.org/0000-0001-8661-9178
Margaret S. Torn https://orcid.org/0000-0002-8174-0099
Date of this Version
Dengel, S., Billesbach, D., & Torn, M. S. (2021). Influence of tundra polygon type and climate variability on CO2 and CH4 fluxes near Utqiagvik, Alaska. Journal of Geophysical Research: Biogeosciences, 126, e2021JG006262. https://doi. org/10.1029/2021JG006262
Arctic tundra has the potential to generate significant climate feedbacks, but spatial complexity makes it difficult to quantify the impacts of climate on ecosystem-atmosphere fluxes, particularly in polygonal tundra comprising wetter and drier polygon types on the scale of tens of meters. We measured CO2, CH4, and energy fluxes using eddy covariance for 7 yr (April to November, 2013–2019) in polygonal tundra near Utqiagvik, Alaska. This period saw the earliest snowmelt, latest snow accumulation, and hottest summer on record. To estimate fluxes by polygon type, we combined a polygon classification with a flux-footprint model. Methane fluxes were highest in the summer months but were also large during freeze-up and increased with the warming trend in August–November temperatures. While CO2 respiration had a consistent, exponential relationship with temperature, net ecosystem exchange was more variable among years. CO2 and CH4 exchange (June–September) ranged between −0.83 (Standard error [SE] = 0.03) and −1.32 (SE = 0.04) μmol m−2 s−1 and 13.92 (SE = 0.26)—23.42 (SE = 0.45) nmol m−2 s−1, respectively, and varied interannually (p ≤ 0.05). The maximum-influence method effectively attributed fluxes to polygon types. Areas dominated by lowcentered polygons had higher CO2 fluxes except in 2016–2017. Methane fluxes were highest in low-centered polygons 2013–2015 and in flat-centered polygons in subsequent years, possibly due to increasing temperature and precipitation. Sensible and latent heat fluxes also varied significantly among polygon types. Accurate characterization of Arctic fluxes and their climate dependencies requires spatial disaggregation and long term observations.
Plain Language Summary We measured carbon dioxide and methane fluxes for 7 yr (April to November, 2013–2019) in polygonal tundra near Utqiagvik (Barrow), Alaska using eddy covariance (EC). The EC method provides the measurements of vertical flux of transported air parcels by correlation of the fluctuations in carbon dioxide or methane concentration with fluctuations in the vertical wind speed. The ice wedge polygonal tundra area is covered by ponds, drained lake basins, and wetter and drier polygon types on the scale of tens of meters across. This period saw the earliest snowmelt, latest snow accumulation date, and hottest summer on record. To estimate fluxes by polygon type, we combined a polygon classification with a flux-footprint model. The model represents the field of view of the EC system and allows the user to extract the location of the peak contribution. The site was a net carbon sink between June and September in each of the seven years. Areas dominated by low-centered polygons had higher carbon dioxide fluxes except in 2016–2017, while methane fluxes were highest in low-centered polygons 2013–2015 and in flat-centered polygons in subsequent years. This is possibly due to increasing temperature and precipitation. Not only were methane fluxes highest in the summer months but also large during freeze-up and increased with the warming trend in August–November temperatures.