Carbon Cycling-Climate Change Feedback of Thawing Permafrost in Arctic Alaskan Lakes: Monitoring Methane Emissions

Abstract:

Arctic Alaska is being impacted by elevated atmospheric temperatures and one consequence could be intensified emissions of greenhouse gases from Arctic lakes as the underlying permafrost thaws. We measured two pathways for methane release from lakes: diffusion and ebullition. The dissolved CH₄ concentration in the lake will be determined by performing a headspace extraction. Ebullition and diffusive flux will be measured using floating gas chambers at the lake surface and be measured on a set time interval. Furthermore, stable isotope measurements will establish the CH₄ source as biogenic (δ¹³C -61‰) or thermogenic (δ¹³C -41‰). Methane is a very potent greenhouse gas compared to carbon dioxide (CO₂) with a global warming potential of 34 times CO₂ on a one-hundred year time scale. It is important establish the role of CH₄ emissions from Arctic lakes as part of the global CH₄ budget, due to the large carbon reserves that can become active in the carbon cycle from thawing of the underlying permafrost as lake temperature warms. The measurements will be collected throughout the day for about three weeks in August 2015. The CH₄ flux trends will be compared to factors such as time of day, weather conditions, lake temperature, lake depth and size, and concentration of dissolved organic carbon and total nitrogen. The lakes in this study are part of the Circum-Arctic Lakes Observation Network and include 35 lakes on the Arctic Coastal Plain of Alaska. Previous studies have shown that concentrations of CH₄ in these lakes ranges from 1 – 8 micrograms per liter, with diffusive CH₄ fluxes between 2 to 500 g CH₄ per minute. Measured ebulliative fluxes range from 100 to 5000 g CH₄ per minute.