Methane and carbon dioxide content in eroding permafrost soils along the Beaufort Sea coast, Alaska

Abstract

[1] Soil CH4 and CO2 gas contents were determined at 39 sites located along the 1957 km coastline of the Beaufort Sea of northern Alaska. Average soil CH4 concentrations increased with depth into the upper frozen layers, while the CO2 decreased with depth. Over 80% of the CH4 and 46% of the total CO2 were contained in the permafrost portion of the profiles. Overall, average concentrations of CH4 within the soil profiles were correlated to water content (R2 = 0.66, p ≤ 0.01). Concentrations of CO2 were correlated to total organic carbon (R2 = 0.76, p ≤ 0.001) and negatively correlated to water content (R2 = 0.61, p ≤ 0.01). The highest total bank gas concentrations for both gases were found in ice-rich permafrost (average volumetric H2O ≥ 70%). Soils eroded across the coast annually were estimated to contain 3.61 ± 1.35 t CH4 (average 1.86 ± 0.70 g m−2) and 469 ± 128 t CO2 (average 240 ± 65 g m−2). Gas amounts present in annually eroding banks were on the same order of magnitude as amounts emitted per year on an area basis from undisturbed tundra and lakes reported by others for the Arctic and smaller than previous estimates for local coastal anthropogenic sources. Soil stocks of gases, water and total organic carbon indicate that with coastal permafrost degradation gas release is minor in magnitude and importance to C-dynamics when compared to the TOC stocks of the coastline.