Effect of ablation rings and soil temperature on 3-year spring CO₂ efflux along the Dalton Highway, Alaska

Abstract. Winter and spring soil CO₂ efflux measurements represent a significant component in the assessment of annual carbon budgets of tundra and boreal forest ecosystems, reflecting responses to climate change in the Arctic. This study was conducted in order to quantify CO₂ efflux, using a portable chamber system at representative sites along the Dalton Highway. Study sites included three tundra, two white spruce, and three black spruce forest locations during the winter and spring seasons of 2010–2012; the study of these sites promised better understanding of winter and spring carbon contributions to the annual carbon budget, as well as the respective ablation-ring effects during spring. Three-year spring CO₂ efflux depends on soil temperature at 5 cm depth on a regional scale. At their highest, Q₁₀ values were 4.2 × 10⁶, within the exposed tussock tundra of the upland tundra site, which tundra soils warmed from −0.9 to 0.5 °C, involving soil microbial activity. From the forest census (400 m²) of the two white spruce forest sites, CO₂ emissions were estimated as 0.09–0.36 gC m⁻² day⁻¹ in winter and 0.14–4.95 gC m⁻² day⁻¹ in spring, corresponding to 1–3% and 1–27% of annual carbon, respectively. Contributions from spring CO₂ emissions are likely to increase as exposed soils widen in average length (major axis) from the east-, west-, south-, and north-side lengths (minor axis). Considering the periods of winter and spring seasons across tundra and boreal forests, average winter- and spring-seasonal CO₂ contributions to annual carbon budgets correspond roughly to 14–22% for tundra and 9–24% for boreal forest sites during 2011 and 2012. Spring carbon contributions, such as growing season CO₂ emissions, are sensitive to subtle changes at the onset of spring and during the snow-covered period in northern high latitudes, in response to recent Arctic climate change.