Eurasian river spring flood observations support net Arctic Ocean mercury export to the atmosphere and Atlantic Ocean

Significance Elevated levels of mercury in Arctic marine wildlife have been linked to midlatitude anthropogenic mercury emissions which are transported to the Arctic Ocean by air. Modeling studies, however, suggest that Arctic rivers contribute equal amounts of mercury to the Arctic Ocean. In this study, we provide comprehensive mercury data on large Eurasian rivers. We find that the spring flood mercury flux from Eurasian rivers is indeed large, which confirms a new Arctic mercury cycling paradigm: Mid-latitude anthropogenic emissions reach the terrestrial Arctic by air, whereby vegetation uptake transfers atmospheric mercury to tundra and boreal peat soils. Springtime snowmelt subsequently mobilizes peat soil mercury to the Arctic Ocean, where photochemistry drives net export of mercury back to the atmosphere.