| 1. |
- Dastoor, Ashu, et al.
(författare)
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Arctic mercury cycling
- 2022
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Ingår i: Nature Reviews Earth & Environment. - : Springer Nature. - 2662-138X. ; 3:4, s. 270-286
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Forskningsöversikt (refereegranskat)abstract
- Anthropogenic mercury (Hg) emissions have driven marked increases in Arctic Hg levels,which are now being impacted by regional warming, with uncertain ecological consequences. This Review presents a comprehensive assessment of the present-day total Hg mass balance in the Arctic. Over 98% of atmospheric Hg is emitted outside the region and is transported to the Arctic via long-range air and ocean transport. Around two thirds of this Hg is deposited in terrestrial ecosystems, where it predominantly accumulates in soils via vegetation uptake. Rivers and coastal erosion transfer about 80 Mg year−1 of terrestrial Hg to the Arctic Ocean, in approximate balance with modelled net terrestrial Hg deposition in the region. The revised Arctic Ocean Hg mass balance suggests net atmospheric Hg deposition to the ocean and that Hg burial in inner-shelf sediments is underestimated (up to >100%), needing seasonal observations of sediment-oceanHg exchange. Terrestrial Hg mobilization pathways from soils and the cryosphere (permafrost, ice, snow and glaciers) remain uncertain. Improved soil, snowpack and glacial Hg inventories, transfer mechanisms of riverine Hg releases under accelerated glacier and soil thaw, coupled atmosphere– terrestrial modelling and monitoring of Hg in sensitive ecosystems such as fjords can help toanticipate impacts on downstream Arctic ecosystems.
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| 2. |
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| 3. |
- Schartup, Amina T., et al.
(författare)
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Influence of the Arctic Sea-Ice Regime Shift on Sea-Ice MethylatedMercury Trends
- 2020
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Ingår i: Environmental Science & Technology Letters. - : American Chemical Society (ACS). - 2328-8930 .- 2328-8930.
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Tidskriftsartikel (refereegranskat)abstract
- Arctic sea ice regulates the air−sea exchange of volatile mercury (Hg) species like dimethylmercury (DMHg) or elemental Hg and is known to host Hg methylating microbes that produce neurotoxic and biomagnifying monomethylmercury (MMHg). Arctic sea ice accounts for 57% of the total primary production in the Arctic Ocean, suggesting that it could be the main source of MMHg to arctic food webs. Despite this, little is known about Hg concentrations and speciation in arctic sea ice. Here, we report Hg species and show the importance of sea-ice composition on sea-ice methylmercury (MeHg = DMHg + MMHg) budgets. We propose that the shift from older sea ice (lower MeHg) to younger sea ice (higher MeHg) resulted in a 40% increase in MeHg (per square meter of sea ice) since 1979 despite a 45% decline in the total sea-ice volume. Approximately 30% of the MeHg sea-ice budget is DMHg, which means that when the seaice melts in the summer it could contribute 0.03−2.7 pmol of DMHg m−2 day−1 to the atmosphere, which is comparable to diffusion from water (0.48−2.8 pmol of DMHg m−2 day−1). This study shows that the MeHg content of rapidly shrinking arctic sea ice and exposure of sea-ice biota may not be declining as previously thought.
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| 4. |
- Schartup, Amina T., et al.
(författare)
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What are the likely changes in mercury concentration in the Arctic atmosphere and ocean under future emissions scenarios?
- 2022
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Ingår i: Science of the Total Environment. - : Elsevier BV. - 0048-9697 .- 1879-1026. ; 836
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Tidskriftsartikel (refereegranskat)abstract
- Arctic mercury (Hg) concentrations respond to changes in anthropogenic Hg emissions and environmental change. This manuscript, prepared for the 2021 Arctic Monitoring and Assessment Programme Mercury Assessment, explores the response of Arctic Ocean Hg concentrations to changing primary Hg emissions and to changing sea-ice cover, river inputs, and net primary production. To do this, we conduct a model analysis using a 2015 Hg inventory and future anthropogenic Hg emission scenarios. We model future atmospheric Hg deposition to the surface ocean as a flux to the surface water or sea ice using three scenarios: No Action, New Policy (NP), and Maximum Feasible Reduction (MFR). We then force a five-compartment box model of Hg cycling in the Arctic Ocean with these scenarios and literature-derived climate variables to simulate environmental change. No Action results in a 51% higher Hg deposition rate by 2050 while increasing Hg concentrations in the surface water by 22% and <9% at depth. Both “action” scenarios (NP and MFR), implemented in 2020 or 2035, result in lower Hg deposition ranging from 7% (NP delayed to 2035) to 30% (MFR implemented in 2020) by 2050. Under this last scenario, ocean Hg concentrations decline by 14% in the surface and 4% at depth. We find that the sea-ice cover decline exerts the strongest Hg reducing forcing on the Arctic Ocean while increasing river discharge increases Hg concentrations. When modified together the climate scenarios result in a ≤5% Hg decline by 2050 in the Arctic Ocean. Thus, we show that the magnitude of emissions-induced future changes in the Arctic Ocean is likely to be substantial compared to climate-induced effects. Furthermore, this study underscores the need for prompt and ambitious action for changing Hg concentrations in the Arctic, since delaying less ambitious reduction measures–like NP–until 2035 may become offset by Hg accumulated from pre-2035 emissions.
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| 5. |
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| 6. |
- Soerensen, Anne L., et al.
(författare)
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A mass budget for mercury and methylmercury in the Arctic Ocean
- 2016
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Ingår i: Global Biogeochemical Cycles. - 0886-6236 .- 1944-9224. ; 30:4, s. 560-575
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Tidskriftsartikel (refereegranskat)abstract
- Elevated biological concentrations of methylmercury (MeHg), a bioaccumulative neurotoxin, are observed throughout the Arctic Ocean, but major sources and degradation pathways in seawater are not well understood. We develop a mass budget for mercury species in the Arctic Ocean based on available data since 2004 and discuss implications and uncertainties. Our calculations show that high total mercury (Hg) in Arctic seawater relative to other basins reflect large freshwater inputs and sea ice cover that inhibits losses through evasion. We find that most net MeHg production (20Mga(-1)) occurs in the subsurface ocean (20-200m). There it is converted to dimethylmercury (Me2Hg: 17Mga(-1)), which diffuses to the polar mixed layer and evades to the atmosphere (14Mga(-1)). Me2Hg has a short atmospheric lifetime and rapidly degrades back to MeHg. We postulate that most evaded Me2Hg is redeposited as MeHg and that atmospheric deposition is the largest net MeHg source (8Mga(-1)) to the biologically productive surface ocean. MeHg concentrations in Arctic Ocean seawater are elevated compared to lower latitudes. Riverine MeHg inputs account for approximately 15% of inputs to the surface ocean (2.5Mga(-1)) but greater importance in the future is likely given increasing freshwater discharges and permafrost melt. This may offset potential declines driven by increasing evasion from ice-free surface waters. Geochemical model simulations illustrate that for the most biologically relevant regions of the ocean, regulatory actions that decrease Hg inputs have the capacity to rapidly affect aquatic Hg concentrations.
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| 7. |
- Soerensen, Anne. L., et al.
(författare)
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Eutrophication Increases Phytoplankton Methylmercury Concentrations in a Coastal Sea-A Baltic Sea Case Study
- 2016
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Ingår i: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 50:21, s. 11787-11796
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Tidskriftsartikel (refereegranskat)abstract
- Eutrophication is expanding worldwide, but its implication for production and bioaccumulation of neurotoxic monomethylmercury (MeHg) is unknown. We developed a mercury (Hg) biogeochemical model for the Baltic Sea and used it to investigate the impact of eutrophication on phytoplankton MeHg concentrations. For model evaluation, we measured total methylated Hg (MeHgT) in the Baltic Sea and found low concentrations (39 +/- 16 fM) above the halocline and high concentrations in anoxic waters (1249 +/- 369 fM). To close the Baltic Sea MeHgT budget, we inferred an average normoxic water column HgII methylation rate constant of 2 x 10-4 d-1. We used the model to compare Baltic Seas present-day (2005-2014) eutrophic state to an oligo/mesotrophic scenario. Eutrophication increases primary production and export of organic matter and associated Hg to the sediment effectively removing Hg from the active biogeochemical cycle; this results in a 27% lower present-day water column Hg reservoir. However, increase in organic matter production and remineralization stimulates microbial Hg methylation resulting in a seasonal increase in both water and phytoplankton MeHg reservoirs above the halocline. Previous studies of systems dominated by external MeHg sources or benthic production found eutrophication to decrease MeHg levels in plankton. This Baltic Sea study shows that in systems with MeHg production in the normoxic water column eutrophication can increase phytoplankton MeHg content.
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| 8. |
- Soerensen, Anne L., et al.
(författare)
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Selenium concentration in herring from the Baltic Sea tracks decadal and spatial trends in external sources
- 2022
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Ingår i: Environmental Science: Processes & Impacts. - : Royal Society of Chemistry (RSC). - 2050-7887 .- 2050-7895.
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Tidskriftsartikel (refereegranskat)abstract
- Selenium (Se) has a narrow range between nutritionally optimal and toxic concentrations for many organisms, including fish and humans. However, the degree to which humans are affecting Se concentrations in coastal food webs with diffuse Se sources is not well described. Here we examine large-scale drivers of spatio-temporal variability in Se concentration in herring from the Baltic Sea (coastal sea) to explore the anthropogenic impact on a species from the pelagic food web. We analyze data from three herring muscle time series covering three decades (1979–2010) and herring liver time series from 20 stations across the Baltic Sea covering a fourth decade (2009–2019). We find a 0.7–2.0% per annum (n = 26–30) Se decline in herring muscle samples from 0.34 ± 0.02 μg g−1 ww in 1979–1981 to 0.18 ± 0.03 μg g−1 ww in 2008–2010. This decrease continues in the liver samples during the fourth decade (6 of 20 stations show significant decrease). We also find increasing North-South and East-West gradients in herring Se concentrations. Using our observations, modelled Se deposition (spatio-temporal information) and estimated Se river discharge (spatial information), we show that the spatial variability in herring Se tracks the variability in external source loads. Further, between 1979 and 2010 we report a ∼5% per annum decline in direct Se deposition and a more gradual, 0.7–2.0% per annum, decline in herring Se concentrations. The slower rate of decrease for herring can be explained by stable or only slowly decreasing riverine inputs of Se to the Baltic Sea as well as recycling of Se within the coastal system. Both processes can reduce the effect of the trend predicted from direct Se deposition. We show that changing atmospheric emissions of Se may influence Se concentrations of a pelagic fish species in a coastal area through direct deposition and riverine inputs from the terrestrial landscape.
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| 9. |
- 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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