Long-term Observations of CO₂ Fluxes during the Snow-free Period in a High Arctic Dry Tundra

The Arctic is undergoing rapid warming, leading to significant changes in permafrost stability and ecosystem carbon exchange. Arctic tundra ecosystems store nearly half of the world's soil carbon, yet permafrost thaw may enhance carbon dioxide emissions, amplifying climate feedbacks. Despite their importance, large uncertainties remain regarding the role of high latitude permafrost regions in the Arctic carbon cycle. The Canadian Arctic covers extensive and heterogeneous landscapes, emphasizing the need for long-term site-based observations of net ecosystem exchange (NEE). In this study, we quantify and characterize carbon dioxide fluxes during the snow-free period using the eddy covariance method at a dry tundra site in Cambridge Bay, Nunavut, Canada. The analysis is based on nine years of eddy covariance observations collected between 2012 and 2022, excluding 2020 and 2021. Carbon dioxide exchange was examined during the snow-free period from mid-June to early September, when vegetation activity plays a dominant role in ecosystem carbon dynamics. The climate at Cambridge Bay is characterized by cold and dry conditions, with a 30-year mean annual temperature of approximately −13 °C and low annual precipitation (~145 mm), typical of a dry tundra ecosystem. The site has experienced a long-term warming trend of approximately +0.0415 °C per year over the period 1953–2022. Snow cover generally persists from September to May, and snowmelt typically begins in late May to early June, marking the onset of the snow-free and biologically active period. Results show that carbon dioxide fluxes during the snow-free period are strongly influenced by vegetation growth, with peak plant productivity and maximum carbon uptake occurring during the growing season between mid-July and early August. During this period, gross primary production exceeds ecosystem respiration, resulting in net carbon uptake. On average, the growing season NEE was −40.5 g C m⁻², with corresponding gross primary production (GPP) and ecosystem respiration (Reco) of 94.2 g C m⁻² and 53.6 g C m⁻², respectively. Notably, 2017 exhibited an unusually early onset of vegetation activity, leading to enhanced carbon uptake during the snow-free period. These flux estimates highlight the important role of the dry tundra ecosystem at Cambridge Bay in the pan-Arctic carbon dioxide budget. These findings provide robust observational evidence of snow-free period carbon dynamics in a high latitude Arctic dry tundra ecosystem and improve our understanding of how ongoing climate warming may influence carbon fluxes in permafrost regions. This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (RS-2025-24683148)