Explore the vast range of titles available.

High-precision measurements of natural variations in the stable isotopic composition of mercury show great promise as a new tracer of mercury sources and chemical transformations in the environment. We strongly suggest that all laboratories adopt a common means of data correction, standardization, and nomenclature in order to ensure that data from various laboratories can be easily evaluated and compared. We make suggestions for mass bias correction, reporting of mass-dependent and mass-independent isotope variations, and a standard protocol for reporting analytical uncertainties. We also present our measured values for isotope ratios in several mercury standard solutions.

Mercury (Hg) isotopes can be used as tracers of Hg biogeochemical pathways in the environment. The photochemical reduction of aqueous Hg species by natural sunlight leads to both mass-dependent fractionation (MDF) of Hg isotopes and mass-independent fractionation (MIF) of the odd-mass isotopes, with the relation between the MIF for the two odd isotopes being distinct for different photoreduction pathways. Large variations in MDF and MIF are observed in fish and provide new insights into the sources and bioaccumulation of Hg in food webs. MIF in fish can also be used to estimate the loss of methylmercury via photoreduction in aquatic ecosytems.

The end-Triassic mass extinction overlapped with the eruption of the Central Atlantic Magmatic Province (CAMP), and release of CO 2 and other volcanic volatiles has been implicated in the extinction. However, the timing of marine biotic recovery versus CAMP eruptions remains uncertain. Here we use Hg concentrations and isotopes as indicators of CAMP volcanism in continental shelf sediments, the primary archive of faunal data. In Triassic–Jurassic strata, Muller Canyon, Nevada, Hg levels rise in the extinction interval, peak before the appearance of the first Jurassic ammonite, remain above background in association with a depauperate fauna, and fall to pre-extinction levels during significant pelagic and benthic faunal recovery. Hg isotopes display no significant mass independent fractionation within the extinction and depauperate intervals, consistent with a volcanic origin for the Hg. The Hg and palaeontological evidence from the same archive indicate that significant biotic recovery did not begin until CAMP eruptions ceased. The association between Central Atlantic Magmatic Province (CAMP) eruption volatiles and the end-Triassic mass extinction remains ambiguous. Here, the authors present mercury and palaeontological evidence from the same archive and show that significant biotic recovery did not begin until CAMP eruptions ceased.

Mercury emissions from artisanal and small-scale gold mining throughout the Global South exceed coal combustion as the largest global source of mercury. We examined mercury deposition and storage in an area of the Peruvian Amazon heavily impacted by artisanal gold mining. Intact forests in the Peruvian Amazon near gold mining receive extremely high inputs of mercury and experience elevated total mercury and methylmercury in the atmosphere, canopy foliage, and soils. Here we show for the first time that an intact forest canopy near artisanal gold mining intercepts large amounts of particulate and gaseous mercury, at a rate proportional with total leaf area. We document substantial mercury accumulation in soils, biomass, and resident songbirds in some of the Amazon’s most protected and biodiverse areas, raising important questions about how mercury pollution may constrain modern and future conservation efforts in these tropical ecosystems. The Peruvian Amazon is facing the highest known input of mercury pollution of any ecosystem globally. Intact forests located near artisanal gold mining are particularly at risk from this toxin.

Anthropogenic Pb is widespread in the environment including remote places. However, its presence in Canadian Arctic seawater is thought to be negligible based on low dissolved Pb (dPb) concentrations and proxy data. Here, we measured dPb isotopes in Arctic seawater with very low dPb concentrations (average ∼5 pmol · kg−1) and show that anthropogenic Pb is pervasive and often dominant in the western Arctic Ocean. Pb isotopes further reveal that historic aerosol Pb from Europe and Russia (Eurasia) deposited to the Arctic during the 20th century, and subsequently remobilized, is a significant source of dPb, particularly in water layers with relatively higher dPb concentrations (up to 16 pmol · kg−1). The 20th century Eurasian Pb is present predominantly in the upper 1,000 m near the shelf but is also detected in older deep water (2,000 to 2,500 m). These findings highlight the importance of the remobilization of anthropogenic Pb associated with previously deposited aerosols, especially those that were emitted during the peak of Pb emissions in the 20th century. This remobilization might be further enhanced because of accelerated melting of permafrost and ice along with increased coastal erosion in the Arctic. Additionally, the detection of 20th century Eurasian Pb in deep water helps constrain ventilation ages. Overall, this study shows that Pb isotopes in Arctic seawater are useful as a gauge of changing particulate and contaminant sources, such as those resulting from increased remobilization (e.g., coastal erosion) and potentially also those associated with increased human activities (e.g., mining and shipping).

During Arctic springtime, halogen radicals oxidize atmospheric elemental mercury (Hg0), which deposits to the cryosphere. This is followed by a summertime atmospheric Hg0 peak that is thought to result mostly from terrestrial Hg inputs to the Arctic Ocean, followed by photoreduction and emission to air. The large terrestrial Hg contribution to the Arctic Ocean and global atmosphere has raised concern over the potential release of permafrost Hg, via rivers and coastal erosion, with Arctic warming. Here we investigate Hg isotope variability of Arctic atmospheric, marine, and terrestrial Hg. We observe highly characteristic Hg isotope signatures during the summertime peak that reflect re-emission of Hg deposited to the cryosphere during spring. Air mass back trajectories support a cryospheric Hg emission source but no major terrestrial source. This implies that terrestrial Hg inputs to the Arctic Ocean remain in the marine ecosystem, without substantial loss to the global atmosphere, but with possible effects on food webs.

Temporal and spatial variations in sea ice coverage at high Northern Hemisphere latitudes have been shown to affect the photodegradation of methylmercury in seawater and the mercury isotope signatures in biological samples, suggesting the potential of mercury isotopes to reconstruct sea ice variability. Here we study the mercury isotopic composition of a 1500-year sediment profile strongly affected by seal activities on the Fildes Peninsula, King George Island, Antarctic Peninsula. The mass independent isotope fractionation of mercury (represented by Δ 199 Hg) in sediments dominated by seal feces input reflects the Δ 199 Hg of marine methylmercury before entering the food web, documenting the changes in the degree of photodemethylation. We found much higher Δ 199 Hg in sediments deposited during a warm period (~700-1000 years ago), suggesting that reduced sea ice promoted greater photodemethylation. Thus, this study demonstrates the modulation of methylmercury photodegradation by sea ice in the Antarctic, and that mercury isotopes can record historical sea ice changes.

IntroductionThe primary source of anthropogenic atmospheric mercury (Hg) emissions globally is artisanal and small-scale gold mining (ASGM). Estimates of Hg emissions from ASGM are poorly constrained due to a lack of monitoring data and the informal, generally unregulated nature of this industry. Trees accumulate atmospheric gaseous elemental mercury (GEM) in bolewood following stomatal uptake and thus have the potential to be used as biomonitors to quantify the spatial and temporal footprint of Hg emissions from ASGM.MethodsWe collected tree cores from Ficus insipida at three mining-impacted and two remote, unimpacted sites in the Peruvian Amazon (n = 4 trees per site).ResultsWe show that tree ring Hg concentrations were higher near ASGM activity located near mining towns (6.0 ng g−1) compared to remote sites (0.9 ng g−1) and recent tree rings were strongly linearly correlated with atmospheric GEM concentrations across all sites (p < 0.0001, r2 = 0.64), especially in the dry season when there is enhanced ASGM activity (p < 0.0001, r2 = 0.76), highlighting the potential for tree rings to be used as biomonitors for GEM. At the most impacted sites, tree-ring Hg increased over time in response to intensification of ASGM.DiscussionThus far, applications of dendrochemistry to quantify Hg pollution have been largely restricted to coniferous species in temperate regions, but this study shows that tropical species also quantify Hg pollution. We conclude that Ficus insipida is a suitable biomonitor and powerful tool for characterizing the spatial, and potentially temporal footprint of GEM emissions from ASGM in the neotropics.

Our understanding of mantle evolution suffers from a lack of age data for when the mantle geochemical variants (mantle components) developed. Traditionally, the components are ascribed to subduction of ocean floor over Earth history, but their isotopic signatures require prolonged storage to evolve. Here we report U-Pb age results for mantle-derived zircon from pyroxenite xenoliths in Oahu, Hawaii, using laser ablation inductively coupled plasma mass spectrometry and isotope dilution - thermal ionization mass spectrometry. The zircon grains have 14 million-year-old rims, Cretaceous cores, and Proterozoic Lu-Hf model ages which are difficult to reconcile with transport of the pyroxenites in the Hawaiian mantle plume because the ages would have been reset by high temperatures. We suggest the zircons may have been preserved in sub-continental lithospheric mantle. They possibly reached Oahu by asthenospheric transport after subduction at Papua New Guinea or may represent fragments of sub-continental lithospheric mantle stranded during Pangean breakup.