Sustained and intensified lacustrine methane cycling during Early Permian climate warming.

Lakes are a major emitter of the atmospheric greenhouse gas methane (CH 4 ); however, their roles in past climate warming episodes remain poorly understood owing to a scarcity of geological records. Here we report the occurrence of sustained and intensified microbial CH 4 cycling in paleo-Lake Junggar in northwestern China, one of the largest known Phanerozoic lakes, during Early Permian climate warming. High-precision U-Pb geochronology refines the age of the upper Lucaogou Formation to the Artinskian, which marks a major glacial-to-postglacial climate transition. The 13 C-enriched authigenic dolomites indicate active methanogenesis in the anoxic lake sediments, and 13 C-depleted hopanes suggest vigorous methanotrophy in the water column. The intensification of CH 4 cycling coincided with increasing global temperature, as evidenced from elevated continental chemical weathering. Our results suggest that the lacustrine CH 4 emissions acted as a positive feedback to global warming and contributed to the demise of the Late Paleozoic Ice Age.