Total and Methylated Mercury in the Beaufort Sea: The Role of Local and Recent Organic Remineralization

摘要

Mercury is a major contaminant in the Arctic marine ecosystem. While extensive studies have been conducted on mercury in the Arctic's atmosphere and biota, far less is known about the distribution and dynamics of mercury species in the Arctic Ocean. Here, we present vertical profiles for total mercury (Hg_T) and total methylated mercury (MeHg_T, sum of monomethylmercury and dimethylmercury) from the Beaufort Sea of the Arctic Ocean at locations with differing sea ice conditions. The concentration of Hg_T ranged from 0.40 to 2.9 pM, with a surface enrichment that can be attributed to a combination of sea ice-modified atmospheric deposition and riverine input. The concentration of MeHg_T ranged from <0.04 to 0.59 pM, with a subsurface peak occurring at the same depth as a nutrient maximum with lower dissolved oxygen, which is consistent with the recent findings in the Pacific Ocean, Southern Ocean, and Mediterranean Sea. However, unlike die interior ocean regions, the nutrient maximum in the Beaufort Sea is predominantly an advective feature produced over the Chukchi Shelf. On the basis of the short lifetime of monomethyimercury in seawater, we propose that the MeHg_T profile in the Beaufort Sea reflects the local, short-term remineralization of labile organic matter, and not the larger signal of organic remineralization adverted from the Chukchi Sea in the halocline. The finding that MeHg_T is produced locally, reflecting recent strength of organic matter cycling, not only explains wide variance in MeHg_T in seawater and biota over time and space, but also implies that MeHg_T could be used as an indicator of the recent export flux of labile organic matter.