Northern regions are warming at 4x the rate of the rest of the world (Rantanen et al. 2022), leading to projected increases in methane (CH₄) emissions from wetlands and lakes (Turetsky et al. 2019). Northern and alpine tundra and forests are potentially significant CH₄ sinks due to their typically dry and well-drained soils (Jørgensen et al. 2015; St. Pierre et al. 2019; Lee et al. 2023; Virkkala et al., 2024) and could offset increasing emissions (Oh et al. 2021). Well-drained ecosystems make up 72% of the northern landscape (Olefeldt et al. 2021), yet the drivers and magnitude of the northern CH₄ sink are poorly constrained. Previous northern research is biased towards CH₄ emissions hotspots, and assumed CH₄ emissions from dry soils were negligible. Thus, CH₄ flux measurements from northern alpine ecosystems are extremely rare (Fig. 1; Kuhn et al. 2021), despite their CH₄ sink potential (Virkkala et al. 2024; Jørgensen et al., 2024).

Vegetation, soil temperature, and soil moisture influence CH₄ uptake (Voigt et al. 2023), but complete understanding of the controls on CH₄ uptake, including links to nitrogen, trace metals, pH, gross primary production (carbon dioxide exchange), microbial dynamics, soil carbon, and response to climate-driven vegetation shifts are understudied (D’Imperio et al. 2023; Voigt et al. 2023; Virkkala et al., 2024). Measurements of CH₄ uptake, and associated controls, from northern alpine ecosystems will improve our ability to scale CH₄ uptake, constrain the northern CH₄ sink, and help predict changes in uptake with climate change.

The core problems to be addressed include 1) constraining the unknown magnitude and drivers of the northern alpine CH₄ sink and 2) assessing the influence of climate change and shifts in alpine vegetation on CH₄ uptake.

Our goals (Fig 1) are to:

1. Improve the representation of northern CH₄ sinks in statistical models to better quantify circumpolar CH₄ uptake through establishing an eddy covariance tower and chamber measurements in an under-represented northern alpine tundra ecosystem.
2. Elucidate the controls on CH₄ uptake including microbial composition and abundance, vegetation, soil carbon and nutrients, trace metals, temperature, and soil moisture.
3. Assess the potential importance of climate change-driven shifts in shrub and tree lines on CH₄ uptake in northern alpine ecosystems.

Success of the project goals can be assessed through model comparisons and upscaling, uncertainty analysis, and hypothesis testing as well as through the completion of a successful field campaign and published papers.

Our project will improve our understanding of the CH₄ uptake in northern alpine environments and will:

• Lead to improved CH₄ uptake models and quantification regionally
• Reduce uncertainties in controls and magnitudes of CH₄ uptake from northern alpine ecosystems
• Improve our understanding of the role of microbial communities, vegetation, and various soil properties on CH₄ uptake, including the impact of changing vegetation (i.e. tree line shifts)