Atmospheric mercury (Hg) in the Arctic shows much weaker or insignificant annual declines relative to northern mid-latitudes over the past decade (2000-2009), but with strong seasonality in trends. We use a global ocean-atmosphere model of Hg (GEOS-Chem) to simulate these observed trends and determine the driving environmental variables. The atmospheric decline at northern mid-latitudes can largely be explained by decreasing North Atlantic oceanic evasion. The mid-latitude atmospheric signal propagates to the Arctic but is there countered by rapid Arctic warming and declining sea ice, which suppresses deposition and promotes oceanic evasion over the Arctic Ocean. The resulting simulation implies a decline of Hg in the Arctic surface ocean that we estimate to be -0.67% yr-1 over the study period. Rapid Arctic warming and declining sea ice are projected for future decades and would drive a sustained decline in Arctic Ocean Hg, potentially alleviating the methylmercury exposure risk for northern populations.