Geothermal activity is a natural source of mercury (Hg) to surface environments, but its contributions as part of the larger geogenic flux to the global Hg budget are poorly understood, in part due to large geographic gaps in emissions data where no measurements have been made. In this study we report the results of a field campaign over 2021 and 2022 on the highly active volcanic island country of Iceland. Six geothermal sites across the country were investigated for soil gaseous elemental mercury (GEM) and total Hg (THg) concentrations through a series of measurements made across the diffuse degassing surface. At 10 cm depth, soil GEM concentrations were often hundreds and in some cases thousands of times higher than ambient surface air concentrations. Geothermal soils were also highly enriched in THg due to the sorption of hydrothermal Hg on the characteristically fine, thermally-altered clays and silts. Soil "hotspots" displayed THg concentrations exceeding 100 mu g g-1 comparable to levels in areas heavily contaminated by anthropogenic activity and in Hg-rich mineral soils. Strong correlations were observed between soil GEM, THg and soil temperature, and intensive measurements made at small spatial scales (-1 m2) demonstrated the representativeness of individual sampling points. By adapting an active sampling gradient method for determining soil-air gas fluxes, we estimate an Icelandic geothermal GEM flux of 1.8 kg a-1 and a total Icelandic GEM flux, including non-geothermal areas, of -18 kg a-1. This work shows that Icelandic geothermal activity can generate high GEM and THg concentrations in the local soil environment, but its contribution to global Hg cycling appears to be minor.

Mercury (Hg) is naturally released by volcanoes and geothermal systems, but the global flux from these natural sources is highly uncertain due to a lack of direct measurements and uncertainties with upscaling Hg/SO2 mass ratios to estimate Hg fluxes. The 2021 and 2022 eruptions of Fagradalsfjall volcano, southwest Iceland, provided an opportunity to measure Hg concentrations and fluxes from a hotspot/rift system using modern analytical techniques. We measured gaseous Hg and SO2 concentrations in the volcanic plume by near-source drone-based sampling and simultaneous downwind ground-based sampling. Mean Hg/SO2 was an order of magnitude higher at the downwind locations relative to near-source data. This was attributed to the elevated local background Hg at ground level (4.0 ng m-3) likely due to emissions from outgassing lava fields. The background-corrected plume Hg/SO2 mass ratio (5.6 × 10-8) therefore appeared conservative from the near-source to several hundred meters distant, which has important implications for the upscaling of volcanic Hg fluxes based on SO2 measurements. Using this ratio and the total SO2 flux from both eruptions, we estimate the total mass of gaseous Hg released from the 2021 and 2022 Fagradalsfjall eruptions was 46 ± 33 kg, equivalent to a flux of 0.23 ± 0.17 kg d-1. This is the lowest Hg flux estimate in the literature for active open-conduit volcanoes, which range from 0.6 to 12 kg d-1 for other hotspot/rift volcanoes, and 0.5-110 kg d-1 for arc volcanoes. Our results suggest that Icelandic volcanic systems are fed from an especially Hg-poor mantle. Furthermore, we demonstrate that the aerial near-source plume Hg measurement is feasible with a drone-based active sampling configuration that captures all gaseous and particulate Hg species, and recommend this as the preferred method for quantifying volcanic Hg emissions going forward.

Volcanic degassing is an important pathway in the geochemical cycling of many elements on Earth.The trace metal mercury (Hg) is emitted from volcanoes and geothermal systems in both gaseous and particulate-bound forms.While other major Hg sources such as anthropogenic emissions have been relatively well characterized, the total flux from volcanic degassing -and its role in the global Hg budget relative to other sourcesremains the subject of debate.More recent estimates suggest the volcanic Hg flux is on the order of ~100 tonnes per year (or <5% of total natural emissions to the atmosphere) [1,2], with the caveat that short-term emissions from explosive eruptions remain unquantified due to the infrequency of these events and challenges for sampling [3].Here we review recent advances in volcanic Hg research, including the results of our extensive multi-year fieldwork in Iceland measuring Hg emissions from two eruptions and several high-temperature geothermal fields across the region.We provide an updated estimate of the global volcanic Hg flux from subaerial volcanic degassing using a recently published 2023 compilation of high-resolution, satellitebased SO 2 fluxes from ~100 persistently degassing volcanoes [4], and a range of Hg/SO 2 mass ratios obtained from recent field measurements.We discuss the likely effects of explosive eruptions on the global atmospheric Hg pool and formulate a time-averaged annual Hg flux from these sources.The poorly understood but potentially important contributions from submarine sources (i.e., mid-ocean spreading ridges, hydrothermal vents) are also discussed in terms of both ocean and atmospheric Hg inputs.

Volcanic systems are challenging environments in which to accurately sample or measure gaseous mercury (Hg) concentrations, as the gas plumes may be hot, acidic and halogen-rich; Hg concentrations may be highly variable; and the environment may not be readily accessible. We conducted an inter-method comparison study of atmospheric Hg measurements at Icelandic volcanic systems using four different methods. These included a passive air sampler (PAS), an active sampler with activated carbon trap (ACT) and two real-time measurement instruments, the Lumex portable mercury analyzer and the Tekran automated mercury analyzer. Good agreement in calculated and time-averaged volcanic plume Hg concentrations (ranging from 2.3 to 7.2 ng m-3) was obtained between the ACT and Lumex methods operated simultaneously at the same sites. In a post-fieldwork intercomparison, ACT and Tekran sampling yielded excellent agreement in measuring background atmospheric Hg concentrations. However, PAS-measured concentrations were significantly lower than the other methods, and in many cases were below the method detection limit, which may be due to the short sampling timeframes and/or adverse meteorological conditions not allowing sufficient Hg to be collected on the samplers. These findings demonstrate that Lumex and ACT methods are suitable for gaseous Hg measurement in volcanic gas plumes.

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-ocean Hg 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 to anticipate impacts on downstream Arctic ecosystems. Mercury is emitted by anthropogenic activities and accumulates in the Arctic. This Review presents a mercury budget for the Arctic, describing fluxes and cycling.

We assessed long-term changes in the feeding ecology and mercury (Hg) accumulation in Eastern High Arctic-Baffin Bay beluga (Delphinapterus leucas) using total Hg and stable isotope (δ13C, δ15N) assays in teeth samples from historical (1854-1905) and modern (1985-2000) populations. Mean δ13C values in teeth declined significantly over time, from -13.01 ± 0.55‰ historically to -14.41 ± 0.28‰ in 2000, while no consistent pattern was evident for δ15N due to high individual variability within each period. The temporal shift in isotopic niche is consistent with beluga feeding ecology changing in recent decades to a more pelagic and less isotopically diverse diet or an ecosystem wide change in isotope profiles. Mercury concentrations in modern beluga teeth were 3-5 times higher on average than those in historical beluga. These results are similar to the long-term trends of Hg and feeding ecology reported in other beluga populations and in other Arctic marine predators. Similar feeding ecology shifts across regions and species indicate a consistent increased pelagic diet response to climate change as the Arctic Ocean progressively warmed and lost sea ice. Previously, significant temporal Hg increase in beluga and other Arctic animals was attributed solely to direct inputs of anthropogenic Hg from long-range sources. Recent advances in understanding the Arctic marine Hg cycle suggest an additional, complementary possibility─increased inputs of terrestrial Hg of mixed anthropogenic-natural origin, mobilized from permafrost and other Arctic soils by climate warming. At present, it is not possible to assign relative importance to the two processes in explaining the rise of Hg concentrations in modern Arctic marine predators.

Dramatic environmental shifts are occuring throughout the Arctic from climate change, with consequences for the cycling of mercury (Hg). This review summarizes the latest science on how climate change is influencing Hg transport and biogeochemical cycling in Arctic terrestrial, freshwater and marine ecosystems. As environmental changes in the Arctic continue to accelerate, a clearer picture is emerging of the profound shifts in the climate and cryosphere, and their connections to Hg cycling. Modeling results suggest climate influences seasonal and interannual variability of atmospheric Hg deposition. The clearest evidence of current climate change effects is for Hg transport from terrestrial catchments, where widespread permafrost thaw, glacier melt and coastal erosion are increasing the export of Hg to downstream environments. Recent estimates suggest Arctic permafrost is a large global reservoir of Hg, which is vulnerable to degradation with climate warming, although the fate of permafrost soil Hg is unclear. The increasing development of thermokarst features, the formation and expansion of thaw lakes, and increased soil erosion in terrestrial landscapes are increasing river transport of particulate-bound Hg and altering conditions for aquatic Hg transformations. Greater organic matter transport may also be influencing the downstream transport and fate of Hg. More severe and frequent wildfires within the Arctic and across boreal regions may be contributing to the atmospheric pool of Hg. Climate change influences on Hg biogeochemical cycling remain poorly understood. Seasonal evasion and retention of inorganic Hg may be altered by reduced sea-ice cover and higher chloride content in snow. Experimental evidence indicates warmer temperatures enhance methylmercury production in ocean and lake sediments as well as in tundra soils. Improved geographic coverage of measurements and modeling approaches are needed to better evaluate net effects of climate change and long-term implications for Hg contamination in the Arctic.

Ocean sediments are the largest sink for mercury (Hg) sequestration and hence an important part of the global Hg cycle 1 . Yet accepted global average Hg flux data for deep-ocean sediments (> 200 m depth) are not based on measurements on sediments but are inferred from sinking particulates 2 . Mercury fluxes have never been reported from the deepest zone, the hadal (> 6 km depth). Here we report the first measurements of Hg fluxes from two hadal trenches (Atacama and Kermadec) and adjacent abyssal areas (2–6 km). Mercury concentrations of up to 400 ng g −1 were the highest recorded in marine sediments remote from anthropogenic or hydrothermal sources. The two trench systems differed significantly in Hg concentrations and fluxes, but hadal and abyssal areas within each system did not. The relatively low recent mean flux at Kermadec was 6–15 times higher than the inferred deep-ocean average 1,3 , while the median flux across all cores was 22–56 times higher. Thus, some hadal and abyssal sediments are Hg accumulation hot-spots. The hadal zone comprises only ~ 1% of the deep-ocean area, yet a preliminary estimate based on sediment Hg and particulate organic carbon (POC) fluxes suggests total hadal Hg accumulation may be 12–30% of the estimate for the entire deep-ocean. The few abyssal data show equally high Hg fluxes near trench systems. These results highlight a need for further research into deep-ocean Hg fluxes to better constrain global Hg models.

Volcanism is a potentially important natural source of mercury (Hg) to the environment. However, its impact on the global Hg cycle remains poorly understood despite advances over the last five decades. This represents a major uncertainty in our understanding of the relative contributions of natural and anthropogenic Hg sources to the global atmosphere. This uncertainty, in turn, impacts evaluation of the effectiveness of policies to mitigate the impact of anthropogenic Hg on the environment. Here we critically review recent progress in volcanic Hg emission research, including advances in sampling methods and understanding of the post-emission behavior of Hg in the atmosphere. Our statistical analysis of the limited available data shows that the plumes of non-arc volcanoes exhibit significantly higher Hg concentrations than arc volcanoes, yet the latter emit 3-fold higher Hg fluxes on average. Arc volcanism also dominates volcanic gas emissions globally, indicating that arc volcanoes should be a priority for future Hg emission research. We explore several methodological challenges that continue to hinder progress in quantifying global volcanic Hg emissions, and discuss the importance of longer time-frame data collection to capture temporal variations in emissions. Recommendations are proposed for working toward a more accurate assessment of the global volcanic Hg flux. A detailed summary of all published volcanic Hg emissions data worldwide is also presented as a reference tool for future work.

The geochemical speciation of total mercury (THg) was examined in pre‐1800 Arctic lake sediments to improve understanding of the factors controlling “natural baseline” THg. Solid‐phase binding forms of THg were determined by sequential extraction of dated cores from three lakes in different ecozones (barren tundra, grassy tundra, and boreal forest). Sediment organic matter (OM) was mostly of algal origin. Mercury was highly concentrated in the sediment OM fraction (OM‐Hg), comprising 60–87% of THg, while OM (as total organic carbon) constituted only 0.6–13% of sediment dry weight (DW). OM‐Hg concentrations were equivalent to 159 ± 13 to 776 ± 215 ng Hg g−1 DW in algal OM and were enriched 2–39 times compared to sediment THg, indicating that even small changes in algal OM inputs could significantly alter THg. OM‐Hg explained 76–96% of the variation in THg concentrations over many centuries. Concentrations of S2 carbon (an algal productivity proxy) and OM‐Hg were significantly correlated in two lakes but not in the boreal forest lake possibly because of OM remineralization in its deep water column. Fluxes of S2 carbon, OM‐Hg, and THg were highly correlated in the barren tundra lake but could not be calculated for the other lakes. The results overall indicate that high algal Hg concentrations due to scavenging of available Hg controlled OM‐Hg flux to sediments, thus driving changes in THg concentrations and fluxes. These findings improve our understanding of the long‐term stability of baseline THg in northern lakes under a changing climate, including in the modern era.

The Minamata Convention to reduce anthropogenic mercury (Hg) emissions entered into force in 2017, and attention is now focused on how to best monitor its effectiveness at reducing Hg exposure to humans. A key question is how closely Hg concentrations in the human food chain, especially in fish and other aquatic wildlife, will track the changes in atmospheric Hg that are expected to occur following anthropogenic emission reductions. We investigated this question by evaluating several regional groups of case studies where Hg concentrations in aquatic biota have been monitored continuously or intermittently for several decades. Our analysis shows that in most cases Hg time trends in biota did not agree with concurrent Hg trends in atmospheric deposition or concentrations, and the divergence between the two trends has become more apparent over the past two decades. An over-arching general explanation for these results is that the impact of changing atmospheric inputs on biotic Hg is masked by two factors: 1) The aquatic environment contains a large inventory of legacy emitted Hg that remains available for bio-uptake leading to a substantial lag in biotic response time to a change in external inputs; and 2) Biotic Hg trends reflect the dominant effects of changes in multi-causal, local and regional processes (e.g., aquatic or terrestrial biogeochemical processes, feeding ecology, climate) that control the speciation, bioavailability, and bio-uptake of both present-day and legacy emitted Hg. Globally, climate change has become the most prevalent contributor to the divergence. A wide range of biotic Hg outcomes can thus be expected as anthropogenic atmospheric Hg emissions decline, depending on how these processes operate on specific regions and specific organisms. Therefore, evaluating the effectiveness of the Minamata Convention will require biomonitoring of multiple species that represent different trophic and ecological niches in multiple regions of the world.

Leadership & writing contribution to Global Mercury Assessment 2018 (Arctic Monitoring and Assessment Programme (AMAP) / United Nation Environment Programme (UNEP). Aquatic Geochemistry team -two chapters . GMA 2018 in press. Several individual legacy publs. on Arctic Hg .

During the past 600 million years of Earth history, four of five major extinction events were synchronous with volcanism in large igneous provinces. Despite improved temporal frameworks for these events, the mechanisms causing extinctions remain unclear. Volcanic emissions of greenhouse gases, SO2, and halocarbons are generally considered as major factors in the biotic crises, resulting in global warming, acid deposition, and ozone layer depletion. Here, we show that pulsed elevated concentrations of mercury in marine and terrestrial sediments across the Triassic-Jurassic boundary in southern Scandinavia and northern Germany correlate with intense volcanic activity in the Central Atlantic Magmatic Province. The increased levels of mercury-the most genotoxic element on Earth-also correlate with high occurrences of abnormal fern spores, indicating severe environmental stress and genetic disturbance in the parent plants. We conclude that this offers compelling evidence that emissions of toxic volcanogenic substances contributed to the end-Triassic biotic crisis.

Most of Canada's Hg comes from global sources, both natural and anthropogenic; 1000s of CDNs impacted by Hg in wild fish & marine mammals; Large uncertainties re natural sources to global atmosphere; Impacts reliability of global budget and modeling; Project will measure Icelandic volcanic Hg fluxes, and understand geological/geochemical controls; Part of planned multinational consortium led by Sanei(Denmark).