Investigation of the Stock Structure of Atlantic Walrus (Odobenus rosmarus rosmarus) in Canada and Greenland Using Dental Pb Isotopes Derived from Local Geochemical Environments

The chemical composition of animal tissues such as teeth appears to reflect an individual's exposure to its geochemical environment. In this study, the lead (Pb) isotope composition of dental cementum was used to investigate the stock structure of Atlantic walrus (Odobenus rosmarus rosmarus) in the Canadian Arctic and Greenland. The 12 communities providing walrus samples for this study represent most of the Canadian and Greenlandic villages where walrus still form an important part of the traditional Inuit diet. Significant differences between locations in mean Pb isotope ratios and the limited overlap of the ranges of values indicate that each village harvested walrus herds that exploited substantially different geological/geographical habitats. This geographic segregation based on isotopic signatures suggests that most walrus stocks (i.e., the groups of walrus that interact with hunters at each community) are more localized in their range than previously thought. 208Pb/207Pb and 208Pb/204Pb were the most important stock discriminators, reflecting the influence of local geological Th/U composition (i.e., 208Pb) on Pb isotope composition in walrus teeth. 204Pb-based isotope ratios in walrus were consistently higher (more radiogenic) and more homogeneous than those in regional terrestrial bedrock, a difference probably due to selective leaching of radiogenic Pb from mineral phases into seawater and mixing during weathering and transport. Dental Pb isotope signatures may have widespread application to stock discrimination of other coastal marine mammal species.La composition chimique de tissus animaux tels que les dents semble refléter l'exposition d'un individu à son milieu géochimique. Pour la présente étude, on a utilisé la composition isotopique du plomb (Pb) contenu dans le cément pour examiner la structure du stock du morse de l'Atlantique (Odobenus rosmarus rosmarus) dans l'Arctique canadien et le Groenland. Les 12 communautés qui ont fourni les échantillons de morse pour ce projet représentent la majorité des villages canadiens et groenlandais où le morse constitue toujours une grande partie du régime alimentaire traditionnel des Inuits. Des différences marquées entre les sites dans la moyenne des rapports isotopiques du Pb et le faible recoupement des gammes de valeurs révèlent que chaque village prélevait des morses au sein de troupeaux qui exploitaient des habitats géologiques/géographiques bien distincts. Cette ségrégation géographique fondée sur des signatures isotopiques suggère que la plupart des stocks de morses (c.-à-d. le groupe de morses qui interagit avec les chasseurs dans chaque communauté) sont plus localisés dans leur territoire qu'on ne le pensait auparavant. 208Pb/207Pb et 208Pb/204Pb étaient les grands caractères discriminants des stocks, reflétant l'influence de la composition géologique locale Th/U (c-à-d. 208Pb) sur la composition isotopique du Pb dans les dents du morse. Les rapports isotopiques fondés sur 204Pb étaient constamment plus élevés (plus radiogéniques) et plus homogènes que ceux du substratum terrestre, la différence étant probablement due à la lixiviation sélective du Pb radiogénique passant des phases minérales dans l'eau de mer et à son mélange durant la météorisation et le transport. Les signatures isotopiques du plomb dentaire peuvent avoir de vastes applications dans la discrimination des stocks d'autres espèces de mammifères marins côtiers

A Comparison of Modern and Preindustrial Levels of Mercury in the Teeth of Beluga in the Mackenzie Delta, Northwest Territories, and Walrus at Igloolik, Nunavut, Canada

Mercury (Hg) concentrations were compared in modern and preindustrial teeth of belugas (Delphinapterus leucas) and walrus (Odobenus rosmarus rosmarus) at sites in the Canadian Arctic so that the relative amounts of natural and anthropogenic Hg in modern animals could be estimated. Mercury levels in the teeth of Beaufort Sea belugas captured in the Mackenzie Delta, Northwest Territories, in 1993 were significantly (p = 0.0001) higher than those in archeological samples dated A.D. 1450-1650. In terms of geometric means, the Hg levels in modern animals were approximately four times as high as preindustrial levels in 10-year-old belugas, rising with age to 17 times as high in 30-year-olds. Because Hg levels in modern teeth were highly correlated with those in soft tissues, including muscle and muktuk, which are part of traditional human diets, it is likely that soft-tissue Hg has increased to a similar degree over the past few centuries. The increase was not due to dietary differences over time, as shown by analysis of stable-C and -N isotopes in the teeth, and was unlikely to be due to sex differences or to chemical diagenesis of historical samples. Industrially related Hg inputs to the Arctic Ocean and Canadian Arctic Archipelago may be the most likely explanation for the increase. If so, then 80-95% of the total Hg in modern Beaufort Sea belugas more than 10 years old may be attributed to anthropogenic activities. In contrast, tooth Hg concentrations in walrus at Igloolik, Nunavut, were no higher in the 1980s and 1990s than in the period A.D. 1200-1500, indicating an absence of industrial Hg in the species at this location.On a comparé les concentrations de mercure (Hg) dans des dents de bélugas (Delphinapterus leucas) et de morses (Odobenus rosmarus rosmarus) de notre époque et de l'ère préindustrielle, à des lieux situés dans l'Arctique canadien de façon à estimer les montants relatifs de Hg naturel et anthropique chez les individus contemporains. Les niveaux de mercure dans les dents de bélugas de la mer de Beaufort capturés en 1993 dans le delta du Mackenzie (Territoires du Nord-Ouest) étaient sensiblement (p = 0,0001) plus élevés que ceux des échantillons archéologiques remontant à une période située entre 1450 et 1650 de notre ère. En termes de moyenne géométrique, les niveaux de Hg chez les animaux actuels étaient près de quatre fois plus élevés que les niveaux préindustriels chez les bélugas âgés de 10 ans, augmentant avec l'âge jusqu'à être 17 fois plus élevés chez les bélugas de 30 ans. Vu que le niveau de Hg dans les dents actuelles était fortement corrélé à celui des tissus mous - y compris les muscles et le muktuk, qui font partie de l'alimentation humaine traditionnelle -, il est probable que la concentration de Hg dans les tissus mous a subi une augmentation similaire au cours des derniers siècles. Comme le montre l'analyse des isotopes de calcium stable et d'azote stable trouvés dans les dents, cette augmentation n'était pas due à des différences alimentaires au cours des années, et elle n'était probablement pas causée par la différence de sexe ou la diagenèse chimique d'échantillons historiques. L'explication la plus plausible de l'augmentation est l'apport de Hg industriel dans l'océan Arctique et l'archipel Arctique. Si tel est le cas, on pourrait attribuer entre 80 et 95 p. cent du Hg total présent chez le béluga actuel de la mer de Beaufort aux activités anthropiques. En revanche, les concentrations de Hg dans les dents de morses provenant d'Igloolik (Nunavut) n'étaient pas plus élevées dans les années 1980 et 1990 qu'au cours de la période située entre 1200 et 1500 apr. J.-C., signalant ainsi l'absence de Hg industriel chez cette espèce à cet endroit

Arctic Sentinels: Global mercury emissions have stabilized over the past decade, yet levels in Arctic marine mammals have risen by an order of magnitude. Scientists struggle to explain why.

Global mercury emissions have stabilized over the past decade, yet levels in Arctic marine mammals have risen by an order of magnitude. Scientists struggle to explain why

Exceptionally low mercury concentrations and fluxes from the 2021 and 2022 eruptions of Fagradalsfjall volcano, Iceland

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 a particularly 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

Toward an assessment of the global inventory of present-day mercury releases to freshwater environments

Aquatic ecosystems are an essential component of the biogeochemical cycle of mercury (Hg), as inorganic Hg can be converted to toxic methylmercury (MeHg) in these environments and reemissions of elemental Hg rival anthropogenic Hg releases on a global scale. Quantification of effluent Hg releases to aquatic systems globally has focused on discharges to the global oceans, rather than contributions to freshwater systems that affect local exposures and risks associated with MeHg. Here we produce a first-estimate of sector-specific, spatially resolved global aquatic Hg discharges to freshwater systems. We compare our release estimates to atmospheric sources that have been quantified elsewhere. By analyzing available quantitative and qualitative information, we estimate that present-day global Hg releases to freshwater environments (rivers and lakes) associated with anthropogenic activities have a lower bound of ~1000 Mg· a−1. Artisanal and small-scale gold mining (ASGM) represents the single largest source, followed by disposal of mercury-containing products and domestic waste water, metal production, and releases from industrial installations such as chlor-alkali plants and oil refineries. In addition to these direct anthropogenic inputs, diffuse inputs from land management activities and remobilization of Hg previously accumulated in terrestrial ecosystems are likely comparable in magnitude. Aquatic discharges of Hg are greatly understudied and further constraining associated data gaps is crucial for reducing the uncertainties in the global biogeochemical Hg budget

Stable isotope food-web analysis and mercury biomagnification in polar bears ( Ursus maritimus )

Mercury (Hg) biomagnification occurs in many ecosystems, resulting in a greater potential for toxicological effects in higher-level trophic feeders. However, Hg transport pathways through different food-web channels are not well known, particularly in high-latitude systems affected by the atmospheric Hg deposition associated with snow and ice. Here, we report on stable carbon and nitrogen isotope ratios, and Hg concentrations, determined for 26, late 19th and early 20th century, polar bear ( Ursus maritimus ) hair specimens, collected from catalogued museum collections. These data elucidate relationships between the high-latitude marine food-web structure and Hg concentrations in polar bears. The carbon isotope compositions of polar bear hairs suggest that polar bears derive nutrition from coupled food-web channels, based in pelagic and sympagic primary producers, whereas the nitrogen isotope compositions indicate that polar bears occupy > fourth-level trophic positions. Our results show a positive correlation between polar bear hair Hg concentrations and δ 15 N. Interpretation of the stable isotope data in combination with Hg concentrations tentatively suggests that polar bears participating in predominantly pelagic food webs exhibit higher mercury concentrations than polar bears participating in predominantly sympagic food webs.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73930/1/j.1751-8369.2009.00114.x.pd

Exceptionally low mercury concentrations and fluxes from the 2021 and 2022 eruptions of Fagradalsfjall volcano, Iceland

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