Distribution characteristics and implications of mercury in the surface sediments of the East Siberian Arctic Shelf

Global warming is leading to permafrost degradation, sea-ice melt, increased river runoff, and changes in ocean dynamics in the Arctic region. These factors, plus the increasing human activities, affects the input and transport of mercury in the Arctic Ocean. We analyzed the mercury content in 87 surface sediments (0～2 cm) sampled in the East Siberian Arctic Shelf in the Chukchi Sea, East Siberian Sea, and Laptev Sea during three Sino-Russian Arctic joint expeditions in 2016, 2018, and 2020 at water depth of 9～2546 m. Results show a significant spatial variability in mercury concentration, which can be divided into the nearshore low-mercury zones (33 ng/g), the middle shelf medium-mercury zone (58 ng/g), and the northern deep water high-mercury zone (84 ng/g). In general, the mercury concentration tended to increase with water depth increasing from nearshore toward offshore. Analyses of sediment grain size, total organic carbon, and specific surface area of sediments show that the mercury concentration was positively correlated with the clay content in the surface sediments, indicating the controlling role of sediment grain size in the distribution of mercury. The coarse sediments in the nearshore showed lower mercury concentration due to the influence of river input, coastal erosion, and hydrodynamic sorting, while the fine-grained sediments in the northern shelf are prone to absorb more mercury. There was a strong positive correlation between mercury and total organic carbon in the Chukchi and Laptev Seas, while the correlation was weaker in the East Siberian Sea due probably to more-complexed source of total organic carbon. The enrichment factor of mercury manifests that the overall level of contamination of sedimentary mercury is low at present in the East Siberian Arctic Shelf area, showing relatively weak influence of human activities.