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| 2. |
- Chen, Long, et al.
(författare)
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A decline in Arctic Ocean mercury suggested by differences in decadal trends of atmospheric mercury between the Arctic and northern midlatitudes
- 2015
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Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 42:14, s. 6076-6083
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Tidskriftsartikel (refereegranskat)abstract
- Atmospheric mercury (Hg) in the Arctic shows much weaker or insignificant annual declines relative to northern midlatitudes over the past decade (2000-2009) but with strong seasonality in trends. We use a global ocean-atmosphere model of Hg (GEOS-Chem) to simulate these observed trends and determine the driving environmental variables. The atmospheric decline at northern midlatitudes can largely be explained by decreasing North Atlantic oceanic evasion. The midlatitude atmospheric signal propagates to the Arctic but is countered by rapid Arctic warming and declining sea ice, which suppresses deposition and promotes oceanic evasion over the Arctic Ocean. The resulting simulation implies a decline of Hg in the Arctic surface ocean that we estimate to be -0.67%yr(-1) over the study period. Rapid Arctic warming and declining sea ice are projected for future decades and would drive a sustained decline in Arctic Ocean Hg, potentially alleviating the methylmercury exposure risk for northern populations.
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| 3. |
- Sonke, Jeroen E., et al.
(författare)
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Global change effects on biogeochemical mercury cycling
- 2023
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Ingår i: Ambio. - : Springer. - 0044-7447 .- 1654-7209. ; 52, s. 853-876
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Forskningsöversikt (refereegranskat)abstract
- Past and present anthropogenic mercury (Hg) release to ecosystems causes neurotoxicity and cardiovascular disease in humans with an estimated economic cost of $117 billion USD annually. Humans are primarily exposed to Hg via the consumption of contaminated freshwater and marine fish. The UNEP Minamata Convention on Hg aims to curb Hg release to the environment and is accompanied by global Hg monitoring efforts to track its success. The biogeochemical Hg cycle is a complex cascade of release, dispersal, transformation and bio-uptake processes that link Hg sources to Hg exposure. Global change interacts with the Hg cycle by impacting the physical, biogeochemical and ecological factors that control these processes. In this review we examine how global change such as biome shifts, deforestation, permafrost thaw or ocean stratification will alter Hg cycling and exposure. Based on past declines in Hg release and environmental levels, we expect that future policy impacts should be distinguishable from global change effects at the regional and global scales.
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| 4. |
- Zhang, Yanxu, et al.
(författare)
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A Coupled Global Atmosphere-Ocean Model for Air-Sea Exchange of Mercury : Insights into Wet Deposition and Atmospheric Redox Chemistry
- 2019
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Ingår i: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 53:9, s. 5052-5061
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Tidskriftsartikel (refereegranskat)abstract
- Air-sea exchange of mercury (Hg) is the largest flux between Earth system reservoirs. Global models simulate air-sea exchange based either on an atmospheric or ocean model simulation and treat the other media as a boundary condition. Here we develop a new modeling capability (NJUCPL) that couples GEOS-Chem (atmospheric model) and MITgcm (ocean model) at the native hourly model time step. The coupled model is evaluated against high-frequency simultaneous measurements of elemental mercury (Hg-0) in both the atmosphere and surface ocean obtained during five published cruises in the Atlantic, Pacific, and Southern Oceans. Results indicate that the calculated global Hg net evasion flux is 12% higher for the online model than the offline model. We find that the coupled online model captures the spatial pattern of the observations; specifically, it improves the representation of peak seawater Hg-0 (Hg-aq(0)) concentration associated with enhanced precipitation in the intertropical convergence zone in both the Atlantic and the Pacific Oceans. We investigate the causes of the observed Hg-aq(0) peaks with two sensitivity simulations and show that the high Hg-aq(0) concentrations are associated with elevated convective cloud mass flux and bromine concentrations in the tropical upper troposphere. Observations of elevated Hg-aq(0) concentrations in the western tropical Pacific Ocean merit further study involving BrO vertical distribution and cloud resolving models.
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| 5. |
- Zhang, Yanxu, et al.
(författare)
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A Global Model for Methylmercury Formation and Uptake at the Base of Marine Food Webs
- 2020
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Ingår i: Global Biogeochemical Cycles. - 0886-6236 .- 1944-9224. ; 34:2
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Tidskriftsartikel (refereegranskat)abstract
- Monomethylmercury (CH3Hg) is the only form of mercury (Hg) known to biomagnify in food webs. Here we investigate factors driving methylated mercury [MeHg = CH3Hg + (CH3)(2)Hg)] production and degradation across the global ocean and uptake and trophic transfer at the base of marine food webs. We develop a new global 3-D simulation of MeHg in seawater and phyto/zooplankton within the Massachusetts Institute of Technology general circulation model. We find that high modeled MeHg concentrations in polar regions are driven by reduced demethylation due to lower solar radiation and colder temperatures. In the eastern tropical subsurface waters of the Atlantic and Pacific Oceans, the model results suggest that high MeHg concentrations are associated with enhanced microbial activity and atmospheric inputs of inorganic Hg. Global budget analysis indicates that upward advection/diffusion from subsurface ocean provides 17% of MeHg in the surface ocean. Modeled open ocean phytoplankton concentrations are relatively uniform because lowest modeled seawater MeHg concentrations occur in oligotrophic regions with the smallest size classes of phytoplankton, with relatively high uptake of MeHg and vice versa. Diatoms and synechococcus are the two most important phytoplankton categories for transferring MeHg from seawater to herbivorous zooplankton, contributing 35% and 25%, respectively. Modeled ratios of MeHg concentrations between herbivorous zooplankton and phytoplankton are 0.74-0.78 for picoplankton (i.e., no biomagnification) and 2.6-4.5 for eukaryotic phytoplankton. The spatial distribution of the trophic magnification factor is largely determined by the zooplankton concentrations. Changing ocean biogeochemistry resulting from climate change is expected to have a significant impact on marine MeHg formation and bioaccumulation.
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