UC Davis

The regional warming of high latitude ecosystems, such as the Arctic tundra, is occurring at an accelerated rate relative to the global average due to a considerable number of positive feedbacks. These ecosystems contain one of the largest terrestrial reservoirs of carbon and nitrogen, locked in the soil column by low temperatures and slow decomposition. However, warming temperatures are increasing emissions of primary greenhouse gases (GHG): carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) from these immense Arctic reservoirs. Increased release of greenhouse gases from permafrost dominated regions is providing a strong positive feedback on climate warming.While attention to GHG dynamics in permafrost regions has increased over the past decade, understanding patterns and controls on GHG emissions due to seasonality and spatial heterogeneity are still poorly understood. This is particularly true for non-CO2 greenhouse gas fluxes CH4 and N2O which are still understudied. Here, I use a combination of data from a network of eddy covariance towers, soil carbon measurements, and chamber flux measurements on the Arctic Coastal Plain to better understand the seasonal and spatial controls on GHG emissions from the Alaskan Arctic. I show that the timing and magnitude of carbon (CO2 & CH4) fluxes can be highly variable (77-107 g C-CO2-eq m-2 year-1) based on mesoscale (<1 km) hydrological status. While fall CH4 emissions comprise up to 45% of the annual regional CH4 budget, there has been uncertainty as to whether emissions of CH4 during the fall are the product of active methanogenesis or the release of stored methane generated during the prior growing season. Here, I show that fall methane emissions (1100±50 mg C-CH4 m-2) outweigh methane storage within the soil active layer (106.8±7.9 mg C-CH4 m-2 - 35cm depth). These results indicate that the dominant source of CH4 emissions during the cold period is likely microbial activity rather than the release of stored methane. Finally, while emissions of N2O have been thought negligible in Arctic wetlands due to low nitrogen mineralization and high plant-microbe competition for inorganic nitrogen, I show that features of the landscape that are collapsing due to ice wedge and permafrost degradation are important N2O sources, as high as 38.6 mg N m-2 d-1, more than an order of magnitude higher than previously assumed. This understanding of trends, budgets, and drivers of GHG fluxes in the Arctic is intended to help increase accuracy in regional and global climate model projections.