Late-Summer Tundra Methane Concentrations and Fluxes on the North Slope of Alaska

Abstract:

Scientific evidence indicates wide-scale changes in Arctic climate. The Arctic contains large expanses of tundra with permafrost, or permanently frozen subsoil. Climate change impacts on the tundra have the potential to enhance biogenic methane (CH₄) production in thawed, active soils or release CH₄ trapped in or below the permafrost. Methane is a highly effective greenhouse gas so CH₄ released from thawing tundra or melting massive ice features constitutes a potential positive feedback to Arctic climate change. In August, 2013 the U.S. Naval Research Laboratory (NRL-6114) led an expedition to investigate late-summer tundra CH₄ concentrations and fluxes on the North Slope of Alaska near Prudhoe Bay. Permafrost cores were collected to measure tundra CH₄ concentrations and soil parameters and a series of gas traps were deployed to measure tundra CH₄ flux at 9 locations spread across a study area of ~1800 km². Thaw probe measurements at each site provided information on the depth of the seasonally-thawed (active) layer. Results show large differences in tundra CH₄ concentrations with depth through the active layer and into the upper permafrost terrain and fine-scale variability in daily CH₄ flux over a relatively small spatial area. It is likely that variations in biogeochemical and geomorphological characteristics such as soil composition, microbial activity, moisture type, active layer composition and extent from site-to-site control the CH₄ regime. In order to provide more accurate estimates of permafrost tundra CH₄ storage and fluxes, controls on CH₄ variability from location to location must be better understood. Further research is required to quantify and predict tundra CH₄ flux in order to better understand the potential impact it will have on Arctic climate, particularly if, as predicted, climate warming leads to the liberation of permafrost carbon in these landscapes.