Vegetation phenology and carbon and energy fluxes in arctic tundra

Background/Question/Methods

Arctic carbon and energy fluxes will respond to climate change, but attribution of these responses to climate remains challenging because measured fluxes are the sum of multiple processes that respond differently to the environment. For example, net ecosystem exchange of CO₂ is the net result of gross carbon uptake by plant photosynthesis and gross carbon loss by heterotrophic and autotrophic respiration; similarly, evapotranspiration is the sum of both evaporation and transpiration. Transpiration, gross carbon uptake, and vegetation phenology are inherently coupled because leaf stomata are the primary regulators of gas exchange. Incorporating this coupling into ecosystem models may improve the attribution of environmental change to measured changes in the net fluxes. In this study, carbon and energy fluxes measured with eddy covariance and continuous vegetation phenology measures from the north slope of Alaska were assimilated within an ensemble Kalman filter (EnKF) into a coupled carbon and energy model to partition latent energy into evaporation and transpiration, and the net ecosystem exchange of CO₂ into gross canopy photosynthesis and ecosystem respiration. 

Results/Conclusions

The incorporation of latent energy and phenology information improved model performance. We explore the utility of the model and data assimilation for improving model performance at a variety of sites in the north slope of Alaska over multiple growing seasons, where long photoperiods in the growing season limit the partitioning of net ecosystem exchange of CO₂ into its components.