Contrasting distributions of dissolved gaseous mercury concentration and evasion in the North Pacific Subarctic Gyre and the Subarctic Front

Abstract The distribution of dissolved gaseous mercury (DGM) and the oxidation–reduction processes of mercury (Hg) in the surface and subsurface ocean are currently understudied despite their importance in ocean–atmosphere interactions. We investigated the Hg(0) evasion and the DGM distribution at water depths of 2–500 m in the Subarctic Front, Western Subarctic Gyre, and Bering Sea of the Northwestern Pacific. The mean DGM concentration in the surface mixed water ( −2  h −1 , respectively), which typically has lower nutrient levels and higher primary production, than in the Western Subarctic Gyre and the Bering Sea (74±18 fM and 3.2±1.2 pmol m −2  h −1 , respectively). The variation in the chlorophyll-a concentration and extracellular protease activity predicted 54% and 48% of the DGM variation, respectively, in the euphotic zone (2–50 m). The DGM concentration in aphotic intermediate water (415±286 fM) was positively correlated to the apparent oxygen utilization (AOU; r 2 =0.94 and p r 2 =0.61 and p =0.01 fo r the Subarctic Front), emphasizing the importance of microbial oxidation of organic matter. The DGM-to-AOU ratio in aphotic water was significantly ( p