Research advances in mercury cycling in Arctic tundra permafrost environments

The Arctic tundra permafrost region is a critical zone for mercury (Hg) biogeochemical cycling. This review systematically synthesizes the sources, transport, and transformation of Hg in Arctic tundra permafrost environments and their responses to climate change. Vegetation uptake of atmospheric gaseous elemental mercury and subsequent litterfall deposition constitute the dominant Hg input pathway, accounting for approximately 70% of total ecosystem Hg deposition. Arctic permafrost stores vast amounts of Hg bound to organic matter, representing a globally significant Hg reservoir. Satellite observations reveal accelerated permafrost thaw and a sustained increase in the normalized difference vegetation index over the past four decades. Active layer deepening and thermokarst development remobilize previously sequestered Hg, delivering it via riverine transport and coastal erosion to aquatic ecosystems, where microbial methylation produces toxic methylmercury, thereby increasing Hg exposure risks for Arctic indigenous communities and wildlife. The complex feedbacks between vegetation succession and permafrost degradation may jointly regulate terrestrial–atmosphere Hg exchange and the subsequent transport and transformation of Hg. However, the response of vegetation-mediated Hg sequestration to environmental change and the mechanisms of Hg remobilization during permafrost thaw remain poorly understood. Future research should prioritize long-term continuous Hg flux observations coupled with isotope tracing to elucidate coupled vegetation–permafrost Hg dynamics, identify microbial drivers of methylation and demethylation in thermokarst wetlands and lakes, and integrate modeling to assess regional- to global-scale impacts of permafrost Hg release.