A new study suggests that rivers may be funneling far more toxic mercury into the Arctic Ocean than previously believed, a finding that may portend even greater mercury concentrations in the future as the effects of climate change accelerate the region’s hydrological cycle. Despite the Arctic’s remoteness, scientists have long known that mercury levels in Arctic mammals are among the highest on the planet, a factor largely attributed to mercury being deposited in the Arctic Ocean from the air. But according to Harvard scientists, circumpolar rivers — particularly three Siberian rivers, the Lena, Ob, and Yenisei — may be contributing twice as much mercury as the atmosphere. According to the scientists, mercury levels in the Arctic tend to increase sharply during the spring and summer. Using a sophisticated model of atmospheric and ocean conditions, they concluded the only factor that could explain this spike was increased flow of these rivers as they melt. According to the researchers, more mercury may be entering the river systems as melting permafrost increasingly releases mercury locked in the soil. In addition, mercury is likely coming from runoff from gold, silver, and mercury mines in Siberia. The study is published in Nature Geoscience.