Long-term variations in wintertime Arctic frontal positions and their mercury anthropogenic emission impacts

Wintertime Arctic frontal positions can be particularly important in determining the inclusion of mercury emissions from anthropogenic sources in the Arctic. Using the streamline confluence method, we constructed a climatology of wintertime (November-March) Arctic frontal positions during 1988-2017, examined their longterm variations, and assessed the impact of such variations on Arctic anthropogenic mercury emissions. The 30 year average positions of wintertime Arctic fronts exhibited similar spatial variability with a latitudinal range of 39 degrees N-67 degrees N over North America and Eurasia. Great interannual variations were found in wintertime Arctic frontal positions with year-to-year shifts spanning up to -10 degrees latitudes over western North America and East Asia. Statistically insignificant trends were found in Arctic frontal positions over North America and Eurasia. The longterm variations in Arctic frontal positions have partly superseded the impact of a steady decreasing trend in North American anthropogenic mercury emissions over the past decades leading to no significantly detectable trend in North American contribution within the Arctic Dome. A maximum increase of >50% was found in emissions from North American anthropogenic sources within the Arctic Dome corresponding to a similar to 3 degrees southward shift in Arctic frontal position compared to the 30-year average. In Asia and Europe, the northward shifts in Arctic frontal positions in some winters have counteracted the impacts of increasing and decreasing, respectively, trends in anthropogenic emissions in the past decades, which offset the impact of total Eurasian anthropogenic emissions by 5.3% from 1988 to 2012. This is the first study to examine and quantify the impact of long-term variations in Arctic frontal positions on Arctic anthropogenic emissions of mercury; it provides insight into one most direct, immediate impact of climate change on anthropogenic emissions in the Arctic.