Evidence of past anaerobic oxidation of methane from coastal sediments

Coastal systems are particularly sensitive to climate divers such as sea-level rise and environmental evolution, playing important roles in greenhouse gas sink and carbon sequestration. Despite the anaerobic oxidation of methane (AOM) consumes 90% of global methane (CH4) produced by marine sediments, and AOM rates are also considerable in freshwater environments, most attention was paid to AOM in surface sediments, and little work has addressed the potential occurrence of AOM from coastal systems in the geological past and its interaction with climate change. A 60-m-long sediment core was investigated at the Qiantang River (QR) mouth, eastern China. The QR incised valley underlies the main part of the modern QR estuary, its sediment fill recorded the complete postglacial transgressive-regressive cycle in response to Holocene sea-level rise. Combining sedimentary Fe and P speciation with the distribution of vivianite and 34S-enriched pyrite, the sulfate-driven AOM (SD-AOM) was proved to occur at the depth interval of 38.8-39.6 m, a transition zone between two stratigraphic units (paleo-estuarine and offshore shallow marine). The intense and sustained SD-AOM is likely triggered by the rapid sea-level jump and plays a critical role in CH4 and P sink, which gives us a new perspective on understanding the elemental cycling and climate change in coastal systems in the past.