WARM EOCENE CONDITIONS MAINTAINED BY METHANOGENESIS IN ARCTIC SOILS

The strikingly large carbon isotope separation (d¹³C_cc - d¹³C_om = 30.5 ‰) between fossilized wood and pedogenic carbonate intertwined in an unusually well-preserved Metasequoia stem of Eocene age from Axel Heiberg Island indicated an Arctic paleoenvironment in which 23% of soil-respired CO₂ was enzymatically reduced to methane, prior to the precipitation of pedogenic carbonate. Using conservative estimates of biomass and litter paleoproduction for Metasequoia fossil forests, I calculated an annual methane release of 341 x 10¹² gCH₄/yr for the forested Arctic during the Eocene. This value is ~3x total modern natural methane emissions from soils, and would have drastically interfered with re-radiation of heat from the Earth's surface, and maintained the relatively mild Arctic temperatures evidenced by the fauna and flora of the Eocene.