Modeling the Mercury Cycle in the Sea Ice Environment: A Buffer between the Polar Atmosphere and Ocean

Total mercury accumulation in Antarctic krill (Euphausia superba) in the northern Antarctic Peninsula during late autumn to early winter

Antarctic krill (Euphausia superba) is a key species in the Antarctic marine ecosystem and also the largest fishery in terms of catch in the Southern Ocean. Bransfield Strait on the northern Antarctic Peninsula is a key fishing ground. Mercury is a globally recognized toxic element that can affect pelagic organisms through bioaccumulation and biomagnification. Understanding mercury dynamics in krill is crucial for understanding its impacts on Antarctic food webs and potential impacts on the uses of krill in the human food chain. However, the factors influencing Hg accumulation in krill remain unclear, especially in the autumn when there is a transition from an environment of abundant food to a period of lower abundance in winter. We therefore investigated the total mercury (THg) accumulation in krill using randomly collected samples (n = 60) from the krill fishery in the Bransfield Strait from 14 May to June 15, 2023. We further explored the potential drivers influencing THg accumulation in krill. The results indicated that THg levels in male krill (46.7 ± 10.8 ng g-1) are comparable to those in females (40.0 ± 7.8 ng g-1), and that krill THg levels in May (47.1 ± 11.5 ng g-1) are significantly higher than in June (41.3 ± 8.2 ng g-1), indicating seasonal variation in krill THg levels. Moreover, the THg concentration of krill showed a significant positive correlation with krill size, regardless of sex or month. Krill size and sex, slope, water mass at 100 m, and sea ice dynamics all affected THg accumulation. Briefly, the THg level decreased with the increases in seafloor slope, and krill accumulated higher level of THg in the open water compared to ice-covered regions, highlighting the importance of seafloor slope and sea ice dynamics in THg dynamics in krill.

In-situ adsorption-coupled-oxidation enabled mercury vapor capture over sp-hybridized graphdiyne

Developing efficient and sustainable carbon sorbent for mercury vapor (Hg0) capture is significant to public health and ecosystem protection. Here we show a carbon material, namely graphdiyne with accessible sp-hybridized carbons (HsGDY), that can serve as an effective "trap" to anchor Hg atoms by strong electron-metal-support interaction, leading to the in-situ adsorption-coupled-oxidation of Hg. The adsorption process is benefited from the large hexagonal pore structure of HsGDY. The oxidation process is driven by the surface charge heterogeneity of HsGDY which can itself induce the adsorbed Hg atoms to lose electrons and present a partially oxidized state. Its good adaptability and excellent regeneration performance greatly broaden the applicability of HsGDY in diverse scenarios such as flue gas treatment and mercury-related personal protection. Our work demonstrates a sp-hybridized carbon material for mercury vapor capture which could contribute to sustainability of mercury pollution industries and provide guide for functional carbon material design.

Oceanic evasion fuels Arctic summertime rebound of atmospheric mercury and drives transport to Arctic terrestrial ecosystems

Mercury (Hg) contamination poses a persistent threat to the remote Arctic ecosystem, yet the mechanisms driving the pronounced summer rebound of atmospheric gaseous elemental Hg (Hg0) and its subsequent fate remain unclear due to limitations in large-scale seasonal studies. Here, we use an integrated atmosphere-land-sea-ice-ocean model to simulate Hg cycling in the Arctic comprehensively. Our results indicate that oceanic evasion is the dominant source (~80%) of the summer Hg0 rebound, particularly driven by seawater Hg0 release facilitated by seasonal ice melt (~42%), with further contributions from anthropogenic deposition and terrestrial re-emissions. Enhanced Hg0 dry deposition across the Arctic coastal regions, especially in the Arctic tundra, during the summer rebound highlights the potential transport of Hg from the pristine Arctic Ocean to Arctic terrestrial ecosystems. Arctic warming, with a transition from multi-year to first-year ice and tundra greening, is expected to amplify oceanic Hg evasion and intensify Hg0 uptake by the Arctic tundra due to increased vegetation growth, underlining the urgent need for continued research to evaluate Hg mitigation strategies effectively in the context of a changing Arctic.

Foraging behavior and sea ice-dependent factors affecting the bioaccumulation of mercury in Antarctic coastal waters

To elucidate the potential risks of the toxic pollutant mercury (Hg) in polar waters, the study of accumulated Hg in fish is compelling for understanding the cycling and fate of Hg on a regional scale in Antarctica. Herein, the Hg isotopic compositions of Antarctic cod Notothenia coriiceps were assessed in skeletal muscle, liver, and heart tissues to distinguish the differences in Hg accumulation in isolated coastal environments of the eastern (Chinese Zhongshan Station, ZSS) and the antipode western Antarctica (Chinese Great Wall Station, GWS), which are separated by over 4000 km. Differences in odd mass-independent isotope fractionation (odd-MIF) and mass-dependent fractionation (MDF) across fish tissues were reflection of the specific accumulation of methylmercury (MeHg) and inorganic Hg (iHg) with different isotopic fingerprints. Internal metabolism including hepatic detoxification and processes related to heart may also contribute to MDF. Regional heterogeneity in iHg end-members further provided evidence that bioaccumulated Hg origins can be largely influenced by polar water circumstances and foraging behavior. Sea ice was hypothesized to play critical roles in both the release of Hg with negative odd-MIF derived from photoreduction of Hg2+ on its surface and the impediment of photochemical transformation of Hg in water layers. Overall, the multitissue isotopic compositions in local fish species and prime drivers of the heterogeneous Hg cycling and bioaccumulation patterns presented here enable a comprehensive understanding of Hg biogeochemical cycling in polar coastal waters.