B080-0010
Influence of tundra polygon type and climate variability on CO2 and CH4 fluxes near Utqiagvik, Alaska
Influence of tundra polygon type and climate variability on CO2 and CH4 fluxes near Utqiagvik, Alaska
Monday, 14 December 2020
Poster
Abstract:
Arctic tundra ecosystems have the potential to generate significant climate feedbacks, but spatial heterogeneity and climate variability make it difficult to quantify the effect of climate conditions on fluxes of trace gases. We measured CO2, CH4, and energy fluxes using the eddy covariance technique during seven years in arctic polygonal tundra near Utqiagvik, Alaska. Polygonal tundra, which covers around 20% of the Arctic Coastal Plain of northern Alaska comprises wetter and drier polygon types on the scale of tens of meters and presents challenges in capturing fluxes associated with these features. We included a polygon type classification in conjunction with a simple application of a footprint model and its ability to predict the maximum effect source location within the footprint and its distance from the EC tower allowing a separation of all fluxes by polygon type. This period saw record snow-free season length, temperatures, and rainfall. Fluxes had high temporal and spatial variability depending reflecting climate conditions and flux-source area. We saw no clear trend in CO2 fluxes over the years. CH4 fluxes were highest in warmest months and showed a clear increasing trend over the past years tracking air temperature with a clear dependency on soil surface temperature, as did values during the freeze-up season later in the year contributing substantially to the annual CH4 emissions.
Based on the location of the maximum flux contribution, areas dominated by low-centered polygons had slightly higher CO2 fluxes during fife years while CH4 fluxes during the first three years and flat-centered the following four years, possibly linked to an increase in air temperature and precipitation. Fluxes ranged between -0.82 and -1.58 µmol m-2s-1 and 13.16 – 26.94 nmol m-2s-1, respectively, showing significant difference at the 5% level across six out of seven years. Sensible and latent heat fluxes also varied significantly, ranging from 35% to 94%, depending on polygon type, implying that flux uncertainties were much higher for some wind directions (and source locations) than others. The maximum influence method applied here captured the site heterogeneity in terms of quantifying the temporal and spatial distribution of CH4 emissions and net carbon fluxes, but also the high variability in energy-flux distribution.
Based on the location of the maximum flux contribution, areas dominated by low-centered polygons had slightly higher CO2 fluxes during fife years while CH4 fluxes during the first three years and flat-centered the following four years, possibly linked to an increase in air temperature and precipitation. Fluxes ranged between -0.82 and -1.58 µmol m-2s-1 and 13.16 – 26.94 nmol m-2s-1, respectively, showing significant difference at the 5% level across six out of seven years. Sensible and latent heat fluxes also varied significantly, ranging from 35% to 94%, depending on polygon type, implying that flux uncertainties were much higher for some wind directions (and source locations) than others. The maximum influence method applied here captured the site heterogeneity in terms of quantifying the temporal and spatial distribution of CH4 emissions and net carbon fluxes, but also the high variability in energy-flux distribution.