Simulating High-latitude Shrubs in the Canadian Land Surface Scheme Including Biogeochemical Cycles (CLASSIC)

Abstract:

The Arctic is undergoing large changes, warming more rapidly than other regions of the world, which is resulting in permafrost thaw and making the large amounts of carbon (C) stored in permafrost areas more vulnerable to decomposition. There are large uncertainties in the Arctic’s carbon dioxide (CO₂) balance, as both respiration and photosynthesis are increasing with higher atmospheric CO₂ concentrations and temperatures, which lead to Arctic greening and shrubification. As recent studies have shown, winter fluxes play an important role in the annual CO₂ balance of Arctic tundra ecosystems. However, year-round measurements at high-latitude sites are difficult to obtain and rare.

Eddy covariance (EC) measurements of net CO₂, water and energy fluxes were made over 14 years at a dwarf-shrub tundra site at Daring Lake (DL1) in Canada’s Southern Arctic ecozone. As EC measurements were not available during the cold season, the process-based ecosystem model CLASSIC (the Canadian Land Surface Scheme including Biogeochemical Cycles, successor to CLASS-CTEM) was used to simulate year-round fluxes. In order to improve the representation of Arctic shrub tundra in CLASSIC, shrub and sedge plant functional types (PFT) were included and results were evaluated using measurements at DL1. Three simulations using the new shrub PFTs, as well as grasses and trees for DL1, were compared. Results indicate that DL1 was an annual CO₂ source during 2004-2017 losing about 200-300 g C m^-2 over the 14-year time period. The joint use of observations and models is valuable in order to better constrain the Arctic CO₂ balance.