Mercury cycling during the last glacial period in Arctic Lake El'gygytgyn, NE Russia

ABSTRACT Tectonic processes play a key role in the global mercury (Hg) cycle on geological timescales, by mobilising Hg from deep Earth reservoirs to the surface. These natural fluxes also introduce a dynamic component to the terrestrial Hg cycle that can interact with other environmental signals and influence Hg delivery to sedimentary records. For records extracted from tectonically active regions, this could complicate, obscure or even preclude accurate interpretation of sedimentary Hg responses to past centennial‐ to millennial‐scale environmental shifts. However, how this influence may translate to the sedimentary record remains unclear. Here, we present one of the longest (~100‐kyr) records of lacustrine Hg accumulation in the Arctic to date from Lake El'gygytgyn, an oligotrophic impact crater located in the remote north‐eastern Russia. Despite the lake's isolated location, anomalously high background Hg values point to a local (non‐atmospheric) source, which we posit is due to upward migration of Hg through faults beneath the lake floor. Superimposed onto this high background flux are a series of large (>900 ng g −1 ) Hg peaks coeval with evidence for a cold and dry climate, characterised by perennial lake‐ice cover, a stratified water column and enhanced organic matter preservation in the sediments. Taken together, this suggests that Hg accumulation is linked to the unusual tectonic setting of Lake El'gygytgyn rather than external (atmospheric) supply, as has previously been observed in Arctic lakes. For example, higher Hg concentrations during phases of perennial ice cover suggest not only that certain climatic conditions further amplify the sedimentary signal from these local inputs, but also that Lake El'gygytgyn may act as a Hg source to the local environment during periods marked by reduced ice coverage.