Search

The article explores how the patent process impacted the development of the isotope industry from 1930 to 1960. The author focuses on the granting of patents to Italian physicist Enrico Fermi for his isotope research, considers the government policies of the U.S., Great Britain, and Canada regarding isotope research after World War II, and explores the legal problems faced by Philips Research Laboratories in maintaining their rights to patents they owned after government legislation was enacted that limited ownership of nuclear technologies. Other subjects discussed include the U.S. McMahon Act, also known as the Atomic Energy Act of 1946, the U.S. Patent Compensation Board, the U.S. Atomic Energy Commission, and the Manhattan Project.

The article discusses a study that aims to examine the effect of temperature and vapour trajectory controls on the stable-isotope signal in the winter snowpacks of the Rocky Mountains in Canada. The researchers used alpine snow-pit data from two alpine field sites at the Haig Glacier, Alberta and the Opabin Glacier in British Columbia. The snow pits that were taken from three different seasons were used to assess the effect of temperature. The study found that separation is driven by the mean temperature of each class and not a direct result of vapour pathway.

Carbon stable isotope analyses have been widely used to estimate terrestrial carbon contribution to lake secondary production. In such approaches, phytoplankton is tacitly assumed as a single, isotopically homogenous source. Such assumption might be valid if (i) zooplankton do not feed selectively on specific algal taxa within bulk phytoplankton, or (ii) although zooplankton do feed selectively, the variability in the δ13C values amongst the different algal taxa is small compared with the variability between the δ13C values of bulk phytoplankton and terrestrial end-members. In a summer field study of six coastal lakes of British Columbia, Canada, we tested these assumptions using gut pigments and stable isotope measures on zooplankton and particulate organic matter. Results revealed that filter-feeding cladocerans positively selected cryptophytes, shown to be substantially 13C-enriched compared with bulk phytoplankton and even with the terrestrial end-member. Comparing a classical two-source mixing model and a model that accounted for algal isotopic heterogeneity, we showed that the use of a classical two-source model can result in an overestimation of terrestrial contribution to zooplankton secondary production. [ABSTRACT FROM AUTHOR]

A method based on isotope dilution headspace solid-phase microextraction and gas chromatography/mass spectrometry was used to assess levels of bisphenol A (BPA) in 56 samples of bottled water products sold in Canada. Levels of BPA in samples of all 51 non-polycarbonate (PC) bottled water products were lower than the method detection limit (0.50 µg l-1). Levels of BPA in most bottled water products in PC carboys were low, ranging from <0.50 to 1.4 µg l-1 with an average of 0.75 µg l-1. However, BPA was detected at levels of 8.8 and 6.5 µg l-1 in two bottles of the bottled water products in PC carboys from the same product analysed over a 5-week period, likely due to accidental or careless exposure of the products to heat (e.g. under the sun) during storage and/or transportation for extended periods of time. [ABSTRACT FROM AUTHOR]

Although lead isotope ratios have been used to identify lead ammunition (lead shotshell pellets and bullets) as a source of exposure for First Nations people of Canada, the actual source of lead exposure needs to be further clarified. Whole blood samples for First Nations people of Ontario, Canada, were collected from participants prior to the traditional spring harvest of water birds, as well as post-harvest. Blood-lead levels and stable lead isotope ratios prior to, and after the harvest were determined by ICP-MS. Data were analyzed by paired t-tests and Wilcoxon Signed-Ranks tests. All participants consumed water birds harvested with lead shotshell during the period of study. For the group excluding six males who were potentially exposed to other sources of lead (as revealed through a questionnaire), paired t-tests and Wilcoxon Signed-Ranks tests showed consistent results: significant (p <0.05) increases in blood-lead concentrations and blood levels of 206Pb/204Pb and 206Pb/207Pb towards the mean values we previously reported for lead shotshell pellets; and a significant decrease in 208Pb/206Pb values towards the mean for lead shotshell pellets. However, when we categorized the group further into a group that did not use firearms and did not eat any other traditional foods harvested with lead ammunition other than waterfowl, our predictions for 206Pb/204Pb, 206Pb/207Pb and 208Pb/206Pb hold true, but there was not a significant increase in blood-lead level after the hunt. It appears that the activity of hunting (i.e., use of a shotgun) was also an important route of lead exposure. The banning of lead shotshell for all game hunting would eliminate a source of environmental lead for all people who use firearms and/or eat wild game. [Copyright &y& Elsevier]

The basement-hosted Bong uranium deposit in the Kiggavik region is associated with a broad hydrothermal alteration halo characterized by an inner illite-rich zone and an outer chlorite-rich zone. The uranium-bearing zones characterized by intense illite alteration yield high δ56Fe and δ26Mg values relative to the host rocks, with average whole-rock values of δ56Fe = 0.58 ± 0.15‰ and δ26Mg = 0.61 ± 0.29‰, and clay-size fraction values of δ56Fe = 0.51 ± 0.20‰ and δ26Mg = 0.82 ± 0.09‰. These isotopic values correlate with a decrease in average Fe2+ concentrations (0.47 versus 2.30 mol% Fe2+ in least-altered hosts). The high δ26Mg values reflect intense illite alteration, which preferentially incorporated heavier magnesium isotopes during alteration of both the ore zones and an upper hematite-altered horizon. Although the clay alteration with high δ56Fe and δ26Mg values coincides with the main uranium-bearing zone, the δ56Fe signatures reflect multiple stages of alteration and mineralization. The high δ56Fe values and lower Fe2+ contents of the uranium-bearing zones support leaching of Fe2+ (aq) enriched in lighter iron isotopes. Sequential leach δ56Fe experiments also indicate that formation of fine-grained iron oxides/hydroxides with positive δ56Fe values (+0.23 to +0.60‰) in late chemical fronts enhanced the primary positive δ56Fe signatures recorded in ore zones. Near surface samples with similar isotopic signatures provide clues to buried mineralization and support structural disruption of the systems after primary mineralization. Distal geochemical expressions of this system may include enrichment in iron contents with negative δ56Fe values and/or negative δ26Mg whole-rock or clay-size fractions values, reflecting precipitation of the isotopically light iron and magnesium leached during hydrothermal alteration. Although more costly to process, sequential leach δ26Mg or δ56Fe analyses produced greater variance in the ore zones relative to background values and removed anomalous values from carbonate minerals. Isotopic analyses of the clay-size fraction produced results comparable to the final digestion in the sequential leach process but this method in particular requires greater understanding the mineralogical controls on the isotopic signatures. [Display omitted] • Application of iron and magnesium isotope methods to hydrothermal uranium deposits • Complex hydrothermal fluid history revealed through iron and magnesium isotopes • Quantifying fluid-rock and redox reactions in the formation of unconformity-related uranium deposits [ABSTRACT FROM AUTHOR]

Abstract: Three curves delineating δ 13C variations across the Early Cambrian Sekwi Formation carbonate ramp, Mackenzie Mountains, Northwest Territories, Canada, are incorporated into a biostratigraphic and sequence stratigraphic framework that provides a higher resolution temporal and spatial framework for the Sekwi Formation. The three δ 13C curves were correlated across a range of depositional environments, from tidal flat to deep subtidal on the Sekwi carbonate ramp. Eight δ 13C “cycles” in the curves (A–H) were correlated across the basin, complimenting the sequence stratigraphic framework. The most complete δ 13C curve from the Sekwi Formation correlates well with a composite Early Cambrian δ 13C curve from the Siberian Platform. However, the differing magnitude and absolute timing of some of the correlative isotopic excursions records the influence of regional tectonism, sea level changes, and diagenesis on the Sekwi ramp. Additionally, the Sekwi Formation δ 13C curve has more high-frequency variations than the Siberian curve, due in part to the higher sample density used to construct the Sekwi curve. The Early–Middle Cambrian boundary was not sampled in this study, but a large negative isotopic excursion in the very latest Early Cambrian coincides with a regional drowning that may be correlative throughout western Laurentia, but recognizing this event globally is problematic. [Copyright &y& Elsevier]

We compared the carbon isotope composition of ecosystem-respired CO2 (δ13CR) from 11 forest ecosystems in Canada and the USA and examined differences among forest δ13CR responses to seasonal variations in environmental conditions from May to October 2004. Our experimental approach was based on the assumption that variation in δ13CR is a good proxy for short-term changes in photosynthetic discrimination and associated shifts in the integrated ecosystem-level intercellular to ambient CO2 ratio (ci/ca). We compared δ13CR responses for three functional groups: deciduous, boreal and coastal forests. The δ13CR values were well predicted for each group and the highest R² values determined for the coastal, deciduous and boreal groups were 0.81, 0.80 and 0.56, respectively. Consistent with previous studies, the highest correlations between δ13CR and changes in environmental conditions were achieved when the environmental variables were averaged for 2, 3 or 4 days before δ13CR sample collection. The relationships between δ13CR and environmental conditions were consistent with leaf-level responses, and were most apparent within functional groups, providing support for our approach. However, there were differences among groups in the strength or significance, or both, of the relationships between δ13CR and some environmental factors. For example, vapor pressure deficit (VPD) and soil temperature were significant determinants of variation in δ13CR in the boreal group, whereas photosynthetic photon flux (PPF) was not; however, in the coastal group, variation in δ13CR was strongly correlated with changes in PPF, and there was no significant relationship with VPD. At a single site, comparisons between our δ13CR measurements in 2004 and published values suggested the potential application of δ13CR measurements to assess year-to-year variation in ecosystem physiological responses to changing environmental conditions, but showed that, in such an analysis, all environmental factors influencing carbon isotope discrimination during photosynthetic gas exchange must be considered. [ABSTRACT FROM AUTHOR]

To determine the sources and sinks of atmospherically deposited Pb at a forested watershed (Plastic Lake) in central Ontario, Canada, Pb pools and fluxes through upland, wetland and lake compartments were measured during 2002/2003 and compared with previous measurements taken between 1989 and 1991. In 2002/2003, annual bulk deposition of Pb was 0.49 mg m−2 compared with 1.90–1.30 mg m−2 in 1989–1991. Annual Pb concentrations in stream water draining the upland part of the catchment were very low (0.04 μg l−1) and were approximately half those measured in 1989–1991 (0.11–0.08 μg l−1). Leaching losses in stream water were small and mass balance estimates indicate almost complete retention (>95%) of atmospherically deposited Pb in upland soils. In contrast, annual Pb concentrations in stream water draining a wetland were between 0.38 and 0.77 μg l−1, with the highest concentration occurring in 2002/2003 and mass balance calculations indicate that the wetland is a net source of Pb in all measured years. Lead concentrations in the lake outflow were low and the average Pb concentration measured in 2002/2003 (0.09 μg l−1) was approximately half the value recorded in 1989–1991 (0.19 μg l−1 both years). Annual mass balance estimates indicate that the lake retained between 2.47 mg m−2 (1989/1990) and 1.42 mg m−2 (2002/2003) and that in 2002/2003 68% of the Pb input to the lake is derived from the terrestrial catchment. These estimates are higher than sediment core records, which indicate around 18 mg m−2 Pb was retained in sediment during the 1990s. Nevertheless, Pb concentrations decrease with sediment depth and 206Pb/207Pb concentrations increase with depth, a pattern also observed in mineral soils that reflects the substantial contribution of anthropogenic Pb to the watershed. Lead isotope data from soil and sediment indicate a recent anthropogenic Pb signal (206Pb/207Pb ∼ 1.185) in upper soils and sediments and an older anthropogenic signal (206Pb/207Pb ∼ 1.20) in deeper soil and sediment. Lead isotope data in sediment and vegetation indicate that practically all the Pb cycled in the forest at Plastic Lake is anthropogenic in origin. [ABSTRACT FROM AUTHOR]

Abstract: Lu–Hf, Sm–Nd and in-situ clinopyroxene Sr and Pb isotope systematics, and mineral major and in-situ trace element compositions were obtained for a suite of non-diamond and diamond-bearing eclogites from the Diavik kimberlites (A154; 55 Ma old), Slave craton (Canada). Temperature estimates of last equilibration in the lithosphere for the non-diamond-bearing Diavik eclogites define two groups; low-temperature (800–1050 °C) and high-temperature eclogites (1100–1300 °C). Most diamond–eclogites indicate temperatures similar to those of the high-temperature eclogites. Isotopic and major and trace element systematics for the non-diamond- and diamond-bearing eclogites indicate overlapping chemical compositions suggesting similar rock formational histories. Calculated whole rock major and trace element abundances using chemical and modal abundances for constituent minerals exhibit broad similarities with mafic cumulates from ophiolite sequences. Most importantly the calculated whole rock eclogite compositions display positive Sr and Eu anomalies, typically interpreted as the result of plagioclase accumulation in cumulate rocks of oceanic crust sequences. Initial whole rock Hf isotopic values and in-situ Sr isotope data from clinopyroxene grains provide evidence that the eclogites were derived from precursor rocks with depleted mantle isotope characteristics. These combined results support the interpretation that the eclogites from Diavik represent remnants of subducted oceanic crust. Lu–Hf isotope systematics indicate that the oceanic protolith for the eclogites formed in the Paleoproterozoic at ∼2.1 Ga, which is in agreement with the in-situ Pb isotope data from clinopyroxene. This result also corroborates the ∼2.1 Ga Lu–Hf model ages recorded by mantle zircons from eclogite found within the Jericho kimberlite in the northern Slave Province (∼200 km northwest of Diavik). The results from both studies indicate a link between eclogite formation and Paleoproterozoic subduction of oceanic lithosphere along the present-day western margin of the Archean Slave craton. [Copyright &y& Elsevier]

The lowering of the water table resulting from peatland drainage may dramatically alter C and N cycling in peatland ecosystems, which contain one-third of the total terrestrial C. In this study, tree annual ring width and C (δ13C) and N (δ15N) isotope ratios in soil and plant tissues (tree foliage, growth rings, and understory foliage) in a black spruce-tamarack (Picea mariana-Larix laricina) mixed-wood forest were examined to study the effects of drainage on tree growth and C and N dynamics in a minerotrophic peatland in west-central Alberta, Canada. Drainage increased the δ15N of soil NH4+ from a range of +0.6‰ to +2.9‰ to a range of +4.6‰ to +7.0‰ most likely through increased nitrification following enhanced mineralization. Plant uptake of 15N-enriched NH4+ in the drained treatment resulted in higher plant δ15N (+0.8‰ to +1.8‰ in the drained plots and -3.9‰ to -5.4‰ in the undrained plots), and deposition of litterfall N enriched with 15N increased the δ15N of total soil N in the surface layer in the drained (+2.9‰) as compared with that in the undrained plots (+0.6‰). The effect of drainage on foliar δ13C was species-specific, i.e., only tamarack showed a considerably less negative foliar δ13C in the drained (-28.1‰) than in the undrained plots (-29.1‰), indicating improved water use efficiency (WUE) by drainage. Tree ring area increments were significantly increased following drainage, and δ13C and δ15N in tree growth rings of both species showed responses to drainage retrospectively. Tree-ring δ13C data suggested that drainage improved WUE of both species, with a greater and more prolonged response in tamarack than in black spruce. Our results indicate that drainage caused the studied minerotrophic peatland to become a more open ecosystem in terms of C and N cycling and loss. The effects of forested peatland drainage or drying on C and N balances deserve further research in order to better understand their roles in future global change. [ABSTRACT FROM AUTHOR]

An extensive study of peridotitic sulfide inclusion bearing diamonds and their prospective harzburgitic host rocks from the 53 Ma Panda kimberlite pipe, Ekati Mine, NWT Canada, has been undertaken with the Re–Os system to establish their age and petrogenesis. Diamonds with peridotitic sulfide inclusions have poorly aggregated nitrogen (<30% N as B centers) at N contents of 200–800 ppm which differs from that of chromite and silicate bearing diamonds and indicates residence in the cooler portion of the Slave craton lithospheric mantle. For most of the sulfide inclusions, relatively low Re contents (average 0.457 ppm) and high Os contents (average 339 ppm) lead to extremely low 187Re/188Os, typically << 0.05. An age of 3.52 ± 0.17 Ga (MSWD = 0.46) and a precise initial 187Os/188Os of 0.1093 ± 0.0001 are given by a single regression of 11 inclusions from five diamonds that individually provide coincident internal isochrons. This initial Os isotopic composition is 6% enriched in 187Os over 3.5 Ga chondritic or primitive mantle. Sulfide inclusions with less radiogenic initial Os isotopic compositions reflect isotopic heterogeneity in diamond forming fluids. The harzburgites have even lower initial 187Os/188Os than the sulfide inclusions, some approaching the isotopic composition of 3.5 Ga chondritic mantle. In several cases isotopically distinct sulfides occur in different growth zones of the same diamond. This supports a model where C–O–H–S fluids carrying a radiogenic Os signature were introduced into depleted harzburgite and produced diamonds containing sulfides conforming to the 3.5 Ga isochron. Reaction of this fluid with harzburgite led to diamonds with less radiogenic inclusions while elevating the Os isotope ratios of some harzburgites. Subduction is a viable way of introducing such fluids. This implies a role for subduction in creating early continental nuclei at 3.5 Ga and generating peridotitic diamonds. [ABSTRACT FROM AUTHOR]

Mercury biomagnifies in aquatic foodwebs in freshwater lakes, and common loons ( Gavia immer) breeding in eastern Canada can be exposed to reproductively toxic concentrations of mercury in their fish prey. We assessed the bioaccumulation and biomagnification of mercury in juvenile and adult common loons, and their preferred prey: yellow perch ( Perca flavescens) in Kejimkujik National Park (KNP), Nova Scotia by measuring mercury levels and stable isotope ratios in tissues. Total mercury levels and stable-carbon (δ13C) and nitrogen isotope ratios (δ15N) were determined in composite whole-fish samples from lakes in KNP and blood samples from juvenile and adult loons captured on lakes in KNP and southern New Brunswick. Geometric mean mercury concentrations were 0.15 and 0.38 μg/g (wet wt.) in small (9-cm fork length) and large (17-cm fork length) yellow perch, and were 0.43 and 2.7 μg/g (wet wt.) in blood of juvenile and adult common loons, respectively. Mercury concentrations in perch and loons were positively associated with body mass and δ15N values. Juvenile loons and large yellow perch had similar mercury levels and δ15N values, indicating similar trophic status despite their 22-fold difference in body mass. Mercury concentrations were higher in yellow perch and common loons in acidic lakes. Our findings highlight the importance of both chemical and ecological factors in understanding mercury biomagnification in lakes and associated risks to fish-eating wildlife. [ABSTRACT FROM AUTHOR]

Abstract: Surface water samples were collected from 55 sites in the Great Lakes Basin and analyzed for the presence of perchlorate using HPLC/MS/MS with an isotopically enriched internal standard. Sites included areas impacted by heavy industry, urbanization, agriculture and atmospheric deposition. Perchlorate was detected at several of the sites at concentrations close to the method detection limit (0.2μg/l). Despite these low concentrations, its presence was confirmed by sample concentration and determination of the isotopic ratio of perchlorate. The presence of perchlorate at two of the sites was related to a fireworks display which had occurred prior to sampling. The other detections of perchlorate were in rivers/creeks draining watersheds which had high density livestock and crop farming activity. We suspect the two are related. To our knowledge, these are the first reported concentrations of perchlorate in Canadian surface waters. [Copyright &y& Elsevier]

Abstract: Beluga (Delphinapterus leucas) continues to be an important food species for Arctic communities, despite concerns about its high mercury (Hg) content. We investigated whether Hg and cadmium (Cd) concentrations had changed during the 20th century in beluga near Somerset Island in the central Canadian Arctic, using well-preserved teeth collected from historical sites (dating to the late 19th century and 1926–1947) and during subsistence hunts in the late 1990s. Mercury concentrations in both historical and modern teeth were correlated with animal age, but 1990s beluga exhibited a significantly more rapid accumulation with age than late 19th century animals, indicating that Hg concentrations or bioavailability in their food chain had increased during the last century. The geometric mean tooth Hg concentration in modern 30 year old animals was 7.7 times higher than in the late 19th century, which corresponds to threefold higher concentrations in muktuk and muscle. Teeth from 1926 to 1947 were similar in Hg content to the late 19th century, suggesting that the increase had occurred sometime after the 1940s. In contrast, tooth Cd was not correlated with animal age and decreased during the last 100 years, indicating that anthropogenic Cd was negligible in this population. Late 19th century beluga displayed a greater range of prey selection (tooth δ 15N values: 15.6–20.5‰) than modern animals (δ 15N: 17.2–21.1‰). To prevent this difference from confounding the temporal Hg comparison, the Hg–age relationships discussed above were based on historical animals, which overlapped isotopically with the modern group. Tooth δ 13C also changed to isotopically more depleted values in modern animals, with the most likely explanation being a significant shift to more pelagic-based feeding. Industrial Hg pollution is a plausible explanation for the recent Hg increase. However, without further investigation of the relationship between the range exploitation of modern beluga and their possible exposure to regional marine food chains with (naturally) higher Hg contents than their historical counterparts, we cannot unequivocally conclude that the increase was anthropogenically driven. [Copyright &y& Elsevier]

Many Phanerozoic time-scale boundaries are characterized by oceanic anoxia and mass extinction events with the deposition of black shale. The Re-Os isotope system in black shale can be used to provide depositional ages for these rocks, thus yielding direct radiometric ages for time-scale boundaries. We demonstrate that the Re-Os black shale geochronometer can yield precise ages useful for time-scale research through study of the Devonian-Mississippian boundary within the Exshaw Formation, Canada. The Re-Os date determined places the Devonian-Mississippian boundary at 361.3 ± 2.4 Ma (2σ including λ uncertainty, model 1, mean square of weighted deviates = 1.2), in accord with recent calibration interpolated from U-Pb zircon dates (360.7 ± 0.7 Ma) for the Hasselbachtal section, Germany. [ABSTRACT FROM AUTHOR]

Monitoring of stable water isotopes ( 18 O and 2 H) in precipitation and surface waters in the Mackenzie River basin of northern Canada has created new opportunities for researchers to study the complex hydrology and hydroclimatology of this remote region [1]. A number of prior studies have used stable isotope data to investigate aspects of the hydrological regime of the wetland-dominated terrain near Fort Simpson, Northwest Territories, Canada [2, 3]. The present paper compares estimates of groundwater contributions to streamflow derived using the WATFLOOD distributed hydrological model, equipped with a new water isotope tracer module, with the results of conventional isotope hydrograph separation [4] for five wetland-dominated catchments along the lower Liard River. The comparison reveals highly promising agreement, verifying that the hydrological model is simulating groundwater flow contributions to total streamflow with reasonable fidelity, especially during the crucial snowmelt period. Sensitivity analysis of the WATFLOOD simulations also reveals intriguing features about runoff generation from channelized fens, which may contribute less to streamflow than previously thought. [ABSTRACT FROM AUTHOR]

Moonmilk, which is often seen coating walls in temperate caves, is a porous secondary calcite deposit composed of an aggregate of microcrystalline calcite and water. This study, based on moonmilk deposits found in Caverne de l'Ours, Ottawa Valley region, proposes a model for its formation based on the calcite and water isotope chemistry and evaluates its use as a climatic proxy. In Caverne de l'Ours, non-calcitic mineral inclusions protrude from the bedrock (Grenville marble) into the moonmilk, while others are entirely enclosed within the moonmilk. This observation suggests a mechanism of bedrock dissolution and reprecipitation for the formation of moonmilk, which is controlled by the changing seasonal climate in the cave. The δ18O of the moonmilk interstial water indicates that the condensation of water vapour occurs mostly in winter and spring. The condensation of water vapour on the surface of the walls allows for the dissolution of the Grenville marble and releases ions necessary for the precipitation of moonmilk. The δ18O and δ13C of calcite and δ18O of the moonmilk interstitial water indicate that precipitation of moonmilk occurs during summer and fall. During these seasons, the relative humidity in the cave decreases resulting in moonmilk growth through the slow evaporation of calcite-saturated water. A comparison of the δ18O record of moonmilk from caves in Gaspésie (Canada) and from Aven d'Orgnac (France) shows that this material retains temperature information valuable for paleoclimatic reconstructions. [ABSTRACT FROM AUTHOR]

The South Mountain Batholith (SMB) of southwestern Nova Scotia is a large, highly differentiated, peraluminous, granitic batholith in which the average A/CNK (mol Al2O3/mol(CaO + Na2O + K2O)) increases from 1.16 to 1.23 with chemical evolution. We use vector analysis of variations solely in Al2O3–(CaO + Na2O + K2O) space to assess the fractionation, assimilation, fluid, and source controls on the peraluminosity of the SMB. With increasing chemical evolution, Al2O3 decreases, CaO decreases sharply, Na2O is approximately constant, and K2O increases in the early and middle stages but decreases in the most evolved stage. Initial 87Sr/86Sr and 143Nd/144Nd isotopic ratios for granites and average Meguma Supergroup country rocks suggest an upper limit of ~33% of wall-rock contamination for the most evolved rocks, if the most primitive rocks are uncontaminated. The trend of chemical evolution of the SMB through Al2O3–(CaO + Na2O + K2O) space is the resultant of all input vectors (processes). In the early stages, those processes are fractional crystallization of plagioclase ± K-feldspar ± cordierite ± biotite and contamination by country rocks. In the later stages, those processes are fractionation of plagioclase ± K-feldspar ± andalusite ± muscovite, further contamination by country rocks, and selective partitioning of Ca–Na–K into aqueous fluid phases. Clear geochemical evidence for variation in the source composition is lacking. [ABSTRACT FROM AUTHOR]

We report on scientific analyses of the only well-preserved ancient human body ever recovered from a North American glacier. The body was found high in the mountains of northwest British Columbia at about 80 km from the nearest point of the strongly indented coast of southern Alaska. The geographical location suggests that the young man, aged about 20 years, could have lived either on the mild coast or in the continental interior. Preliminary environmental scanning electron microscopy (ESEM) and light microscope studies of the contents of the digestive tract reveal pollen of an intertidal salt-marsh plant and pieces of a marine crustacean. Remains of coastal zone plants (a fruit of a flowering plant and a needle of a coniferous tree) had adhered to the deceased's robe. Stable isotope analyses of bone and muscle show that more than 90 % of the dietary protein was from marine sources. We conclude that this individual had strong coastal connections during his life and had been on the coast shortly before he died about 550 to 600 years ago. [ABSTRACT FROM AUTHOR]

Investigations on the distribution of thorium isotopes in the water column have been utilized as powerful tracers to investigate the geochemical pathways of particle-reactive material in the ocean. We measured Th (228Th, 230Th, 232Th and 234Th) isotopes in samples collected along a horizontal profile from Barrow, AK to the Canada Basin as well as two vertical profiles in the Canada Basin. The suspended particle concentrations were also measured to investigate the role of suspended particulate matter (SPM) in Th scavenging.The SPM inventory is more than an order of magnitude higher than that reported for the Alpha Ridge ice station, indicating that the SPM inventories vary over an order of magnitude in the deep Arctic Basins. The conditional partition coefficient of Th isotopes between suspended particulate matter and dissolved phase generally appears to be higher than those in non-polar regions, and this is attributed to more reactive suspended particulate matter. The residence times of total 230Th are significantly lower than those calculated for the Alpha Ridge station, while higher than those found in the Eurasian Basin and Beaufort Sea in the Canadian Basin. The calculated residence time in all the deep basins of the Arctic Ocean varied between 13±1 and 45±1 years. A reversible scavenging model applied to the distribution of Th isotopes (230Th–228Th in the deep waters and 234Th–228Th in the upper 100 m) indicates that the forward removal rate constant is higher than the value reported for the Alpha Ridge while the reverse rate constant is comparable to the Alpha Ridge station suggesting faster removal onto particulate matter and slower desorption of Th from the particulate matter. [Copyright &y& Elsevier]

Gas composition and stable isotope data were integrated to constrain the controls on the occurrence of H2S and CO2 in the subsurface Triassic of the west central Alberta Basin in Canada. Compositional data reveal that the wettest gases occur in the central part of the study area and are flanked by gases of increasing dryness to the east and west. H2S production in the Triassic system is attributed to sulfate reduction. Present temperatures in the subsurface are approximately 60 to 80 °C in the interval of interest. These temperatures are 50 to 55 °C less than the minimum threshold for thermal sulfate reduction (TSR), suggesting that bacterial sulfate reduction (BSR) is the probable mechanism of active H2S generation. Higher temperatures present during previous stages of burial were within the range of thermal sulfate reduction (TSR). Variability in the measured δ34S values of gases in Lower and Middle Triassic strata appears be controlled by dissolved sulfate fluxes from two sulfate sources having disparate δ34S signatures, as well as by the admixing of H2S generated by TSR at previous stages of deeper burial. [Copyright &y& Elsevier]

The article provides information on studies of elemental synthesis in exploding stars using the Detector of Recoils And Gammas Of Nuclear reactions (DRAGON) and the TRIUMF UK Detector Array (TUDA). The goal of the DRAGON experimental program, which is based at the ISAC Radioactive Beams facility in Canada, is to study the probability of reactions involving the capture of hydrogen or helium by a short lived exotic isotope, which results in the emission of electromagnetic radiation only.

Lead concentrations and Pb isotope ratios were measured in the forest floor, mineral soil and vegetation at a white pine and a sugar maple stand in a woodland in south central Ontario. Lead concentrations decreased and 206Pb/207Pb ratios increased with mineral soil depth reflecting the mixing of pollution and natural Pb sources. Lead concentrations and 206Pb/207Pb ratios at 20–30 cm depth were ∼6–7 mg/kg and 1.31–1.32, respectively. Assuming an integrated 206Pb/207Pb ratio in deposition over time of 1.18, estimated from lichen measurements and published data for the region, approximately 65% of Pb in the surface (0–1 cm) mineral soil is from anthropogenic sources. Approximately 90% of pollution Pb is found in the 0–10 cm soil layer (Ah) and less than 3% of the pollution Pb is present in the forest biomass and mull-type forest floor combined. Despite low Pb concentrations in vegetation (<2.5 mg/kg), we estimate that between 65 and 100% of the Pb in vegetation and ∼75% of the Pb in the forest floor is from pollution sources. In total, the pollution Pb burdens at the pine and maple stands are estimated to be 860 and 750 mg/m2, respectively. [Copyright &y& Elsevier]

Fifty new Nd isotope analyses are presented from the North Bay area of the Grenville Province in Ontario. These data are used to map the extent of an allochthonous Grenvillian terrane which is an outlier of the Allochthonous Polycyclic Belt of the Grenville Province. Amphibolite facies orthogneisses from the allochthonous terrane have depleted mantle Nd model ages (T[subDM]) below 1.8 Ga, whereas the gneisses of the structurally underlying parautochthon, almost invariably have model ages above 1.8 Ga. The distribution of model ages is consistent with the distribution of distinct types of metabasic rock, used by other researchers as the criterion for recognizing rocks of the allochthonous and parautochthonous belts of the Grenville Province. The agreement between these different types of evidence demonstrates that Nd isotope mapping is a reliable and powerful tool for mapping terrane boundaries in high-grade metamorphic belts. [ABSTRACT FROM AUTHOR]

Potassic silica-undersaturated mafic volcanic rocks form a minor portion of the predominantly calc–alkaline Eocene Challis–Kamloops volcanic belt, which extends from the northwestern United States into central British Columbia (Canada). Their major occurrence is in the Penticton Group in south central British Columbia, where they reach a thickness of up to 500 m and form the northwestern edge of the Montana alkaline province. These analcime-bearing rocks (∼53–52 Ma old) are typically rhomb porphyries of ternary feldspar (An28Ab52Or20). Additional phenocryst phases include clinopyroxene, analcime, phlogopite and rare olivine. The rocks are characterized by high total alkalis, particularly K2O (>4.5 wt%) as well as by a distinct enrichment of large-ion lithophile elements versus heavy rare-earth elements and high-field-strength elements. They have unusual isotopic compositions compared to most other rocks of the Challis–Kamloops belt, particularly high negative ∊Nd values and elevated but relatively uniform initial 87Sr/86Sr ratios (∼0.7065). The potassic silica-undersaturated rocks overlie Precambrian crust and lithosphere and were at least in part derived from ancient metasomatized subcontinental mantle lithosphere, which was modified in a Precambrian subduction setting. The alkaline rocks of the Challis–Kamloops belt are related to a slab-window environment. In particular, they were formed above the southern edge of the Kula plate adjacent to the Kula–Farallon slab window, whereas the Montana alkaline province situated well to the southeast was formed directly above the Kula–Farallon slab window. Upwelling of the hotter asthenospheric mantle may have been the thermal trigger necessary to induce melting of fertile and metasomatized lithospheric mantle. [Copyright &y& Elsevier]

Presents a study that examined neodymium isotope geochemistry of felsic volcanic and intrusive rocks from the Yukon-Tanana terrane (YTT) in the Finlayson Lake region, Yukon, Canada. Geological setting of the YTT in the Finlayson Lake region; Geochemical attributes of the intrusive rocks; Systematics of the neodymium isotopes.

An isotope-based approach for water balance assessment is presented and applied to estimate throughflow, residence time and catchment runoff to 70 headwater lakes on the Boreal plain and uplands of northern and north-central Alberta, Canada. The survey reveals a complex hydrologic regime with systematic variability in water balance due to local site characteristics. On average, runoff to lakes in wetland-dominated catchments is found to be significantly higher than runoff to upland-dominated lakes, with generally higher contributions from catchments with low bog/fen ratios. The isotope method, which relies primarily on water sampling and isotopic analysis, can be easily integrated in routine water quality surveys and is shown to be a practical alternative to conventional hydrological modelling for comparative analysis of water balance controls on hydrochemistry and aquatic ecology of lakes, particularly in low-relief wetland-rich terrain. [Copyright &y& Elsevier]

• Geochemistry, geochronology and zircon Hf isotopic compositions of the Eoarchean to Neoarchean crust from the Saglek-Hebron Complex (SHC). • The SHC felsic crust formed over one billion years through six distinct magmatic events. • Newly identified Paleoarchean Iluilik magmatic event. • Hadean to Eoarchean mafic crustal source for the SHC TTG. • Reworking of Eoarchean TTG producing granite over one billion years. • Distinct shift to more juvenile Hf isotopic composition at ∼3.2 Ga. • Implications for Earth's early crust evolution. The Saglek-Hebron Complex (SHC) located in Northern Labrador, Canada, includes some of the oldest crustal rocks on Earth. This granite-greenstone terrain is dominated by trondhjemite, Mg-rich tonalite, granite, with subordinate granodiorite, and recorded over one billion years of early magmatic history between ∼3900 Ma and ∼2700 Ma. New in-situ U-Pb analyses on zircons from eighteen rock samples, suggest that six distinct magmatic events formed the felsic crust of the SHC, during the Archean Eon. Age deconvolution analysis constrains these magmatic episodes at ca. 3857 Ma, 3744 Ma, 3575 Ma, 3330 Ma, 3224 Ma and 2750 Ma, respectively defined as the Iqaluk, the Uivak I, the Uivak II, the Iluilik, the Lister and the late granite events. The 3330 Ma Iluilik represents a newly defined magmatic event, distinct from the Lister event previously recognized at ∼3200 Ma. Uranium-Pb geochronology, combined with in-situ Hf isotopic data on zircons and geochemistry of the host rocks, reveal a complex and protracted crustal history of the SHC marked by the reworking of mafic and felsic crust over one billion years. Zircons from the oldest Iqaluk and Uivak I samples yield slightly suprachondritic initial εHf values (up to ∼+4), consistent with the involvement of a long-term depleted source in the Eoarchean. The 3330 Ma Iluilik granodiorite exhibits a low initial εHf value of −6, clearly diverging from the near-chondritic Hf isotopic composition of the 3224 Ma Lister tonalites. Considering a mafic crustal precursor (with a 176Lu/177Hf ratio of ∼0.02) for trondhjemite-tonalite-granodiorite (TTG) samples, the initial Hf isotopic compositions of the SHC Eoarchean to Paleoarchean zircons would be consistent with the reworking of Hadean mafic crust. The zircon εHf vs. time trend for granite samples corresponds to a 176Lu/177Hf ratio of ∼0.01, suggesting that the granitic crust was mainly produced by crustal reworking of the oldest TTG. Similarly to the felsic crust of the Itsaq Gneiss Complex of SW Greenland, the SHC granitoids appear to record a shift to more juvenile compositions at the end of the Paleoarchean. However, contrary to what is observed in SW Greenland, almost no input of juvenile material has been recorded by the SHC Neoarchean felsic crust. [ABSTRACT FROM AUTHOR]

Hinchey (2021) uses new Nd isotope data for metavolcanic and plutonic rocks from the Aillik Domain of the Makkovik Province to propose a reinterpretation of the Makkovik Province, arguing that the Aillik and Cape Harrison domains of the orogen should be combined into a single new domain. However, Hinchey reaches this conclusion by re-plotting the locations of the analysed samples to give the impression that Makkovikian rocks of the Aillik and Cape Harrison domains had similar ranges of (initial) Nd isotope composition. I will show in this comment that Hinchey's claim of largely overlapping Nd isotope signatures in the Aillik and Cape Harrison domains is incorrect, and that multiple lines of isotopic evidence do not support her tectonic model. [ABSTRACT FROM AUTHOR]

Perennial ice from caves on and to the east of the Canadian Great Divide yield δ[sup 18]O and δD values, which are unusually high measurements when compared with the average precipitation for the region. Furthermore, these ice data fall below and along lines of lower slope than the Global Meteoric Water Line. To explain the observed relationships, we propose the following process. A vapour-ice isotopic fractionation mechanism operates on warm-season vapour when it precipitates as hoar ice on entering the caves. The subsequent fall of hoar to the cave floor through mechanical overloading, along with ice derived from ground-water seepage (with a mean annual isotopic composition), results in massive ice formation of a mixed composition. This mixed composition is what is observed in the characteristic relationships found here. Such findings suggest that a warm versus cold climate interpretation for ancient cave ice may be the opposite of that found in the more familiar polar and glacial ice cores. [ABSTRACT FROM AUTHOR]

Investigates the source of a specific neodymium (Nd) isotopic signature seen in miogeoclinal sedimentary rocks of the Canadian Cordillera from Late Devonian time onward. Formation of the Franklinian mobile belt by plate convergence of an unknown landmass; Franklinian orogen as a throughway for voluminous sediments derived from Caledonian mountains.

Presents information on a study on a temporal monitoring of environmental isotopes and geochemistry in ground water within the Raisin River basin, an agricultural watershed in eastern Ontario, Canada. Field sampling and analytical methods; Precipitation and runoff during study period; Seasonal variations in Carbonated geochemistry.

Estimates the temperatures from quartz-Al[sub2]SiO[sub5] pairs from oxygen isotope fractionation of the Mica Greek area, British Columbia. Information on oxygen isotope thermometry; Application of the fast grain boundary diffusion model; Discussion on quartz-kyanite nodules.

Presents a study in which the ...Pb stable isotope ratio tracer was used to decipher the biogeochemical pathway leading to the Pb contamination of freshwater macrophytes and periphyton in a small agricultural watershed of southern Quebec, Canada. How lead ratio and concentration were measured; Where the samples were taken from; Differences in the ...Pb ratio measured for the two main sources of lead contamination, bulk deposition and agricultural soils.

Natural mineral-rich springs which attract moose Alces alces and white-tailed deer Odocoileus virginianus were studied in a small area in central Canada. The spring water was particularly rich in Na and Cl but also contained levels of K, Ca, Mg, HCO3 and Mn higher than nearby stream water. In a selection experiment near a natural spring, aqueous solutions of NaCI, NaHCO3 and Na2SO4 were consumed consistently by the animals while salts of K, Ca and Mg were not. Isotope analysis indicates that the spring waters are part of a modern and probably localized flow system. Evaporite minerals and extensive fractures in the local sedimentary bedrock appear to account for the salt content of the spring waters. [ABSTRACT FROM AUTHOR]

Presents an abstract which deals with Nd isotopes in clastic 600-75 Ma sedimentary rocks from miogeocline of Alberta and British Columbia used to constrain the importance of proximal changes in provenance and develop miogeoclinal for Nd isotopes for input to Cordilleran terranes. History of sedimentation and basin development; Average effects of sedimentation; Indication from the result of the study.

Heavy metal(loid) (Cd, Co, Cr, Ni, Cu, Zn, Pb, V, Tl, and As) and Pb isotope compositions of two black shale weathering profiles were determined to investigate the geochemical behaviors of these toxic elements during black shale weathering and the heavy metal(loid) contamination and source apportionment of Pb in black shale-associated soils. Black shale has higher heavy metal(loid) concentrations than the upper continental crust and the worldwide average shale. In contrast, the surface soils have much higher heavy metal(loid) concentrations than the profile soils. The heavy metal(loid) concentrations in black shale-associated soils are higher than the Chinese and worldwide soil background values, except for Co and Pb. Black shale-associated soils, especially the surface soils, have higher average concentrations of As, Cd, Cr, Ni, Cu, and Zn than Chinese, Dutch, and Canadian soil guidelines. The enrichment factor (EF) and geoaccumulation index (I geo ) values indicate various degrees of heavy metal(loid) contamination in these soils, particularly for the heavy metals Cd, Tl, and V and metalloid As. Co and Pb contamination in these soils is not a current concern. According to the mass transfer coefficient (τ Ta,j ) values, Cd, Co, Ni, and Zn show overall losses, and other metals (Cr, Cu, Pb, and V) exhibit different behavior in the studied black shale weathering profiles. Based on a simple binary Pb isotopic mixing model, black shale is the dominant contributor to the Pb in black shale-associated soils (70.5-91.1% to profile soils and 81.2-88.8% to surface soils), and vehicle exhaust contributes less (8.9-29.5%) to the Pb in profile soils. Vehicle exhaust can exert an impact on the Pb isotopic evolution at depth intervals of 60-80 cm below the soil surface., (© 2021. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

The tempo and magnitude of ocean oxygenation during the rise of animals in the Ediacaran Period (635 to 539 million years ago, or Ma) is debated. Reconciling this debate is key to understanding what role, if any, oxygen played in the rise of large morphologically complex life on Earth. We reconstruct a portion of Ediacaran ocean oxygenation history using thallium isotope records (reported as ε205Tl) captured in shales from South China (Wuhe section) and northwestern Canada (Goz A and Sekwi Brook sections). At first blush, our ε205Tl data from these two locations are very different. South China shales reveal two pronounced and extremely negative Tl isotope excursions, in mid-members II and III of the Doushantuo Formation (where ε205Tl authigenic reach nadirs of −10.4 ± 0.2; 2SD and − 9.1 ± 0.2; 2SD, respectively). In contrast, northwestern Canada shales reveal fairly invariant values (average ε205Tl authigenic = −2.1 ± 1.6; 2SD, n = 75). These disparate records are in much better agreement, however, if we cull from our dataset shales that were inferred in previous work to have been deposited in restricted settings. By comparison to analogous modern settings (e.g., the Black Sea), ε205Tl data in these shales most likely fingerprint local-scale processes. On the other hand, and also by comparison to modern settings (e.g., Cariaco and Santa Barbara basins), shales deposited in an open ocean setting probably captured a globally homogenous seawater ε205Tl (ε205Tl SW). Moving forward with this assumption, we find that Ediacaran open ocean ε205Tl SW values were predominantly comparable to bulk upper continental crust (ε205Tl = ~−2). These relatively heavy open ocean ε205Tl SW imply limited Mn oxide burial in global marine sediments for large periods of time during the Ediacaran, and by inference also limited accumulation of O 2 in global marine bottom waters. Only for what appear to be very brief episodes of time (≪5–10 million years) at ~635 Ma and ~580 Ma did open ocean ε205Tl SW reach values considerably lighter than bulk upper continental crust (for example, ε205Tl SW as low as −4.4 ± 0.2; 2SD at ~635 Ma and − 5.3 ± 0.3: 2SD at ~580 Ma). These much rarer negative ε205Tl SW values require short-lived episodes of globally enhanced Mn oxide burial in marine sediments, and by implication also brief episodes of enhanced accumulation of O 2 in global marine bottom waters. When interpreting geochemical data, it is important to make global-scale inferences only after identifying and accounting for local-scale overprints. Applying this strategy ourselves, we find compelling evidence for an Ediacaran global ocean that only very briefly experienced widespread bottom water oxygenation during the rise of animals. [ABSTRACT FROM AUTHOR]

Honey from Apis mellifera is a useful and inexpensive biomonitor for mapping metal distributions in urban centers. The sampling resolution of a biomonitoring survey (e.g., city versus global scale) determines which geochemical processes are reflected in the results. This study presents Pb isotopic compositions and metal concentrations in honey from around the world, sampled at varying resolutions: honey from Canada (n = 21), the United States (n = 111), Belgium (n = 25), and New Zealand (n = 10), with additional samples from Afghanistan, Brazil, Cuba, Germany, Liberia, Taiwan, and Turkey. Honey was sampled at high resolution in two uniquely different land-use settings (New York Metro Area and the Hawaiian island of Kaua'i), at regional-scale resolution in eastern North America (including the Great Lakes region), and Pb isotopic compositions of all samples were compared on a global scale. At high sampling resolution, metal concentrations in honey reveal spatially significant concentration gradients: in New York City, metals associated with human activity and city infrastructure (e.g., Pb, Sb, Ti, V) are more concentrated in honey collected within the city compared to honey from upstate New York, and metal concentrations in honey from Kaua'i suggest polluting effects of nearby agricultural operations. At lower resolution (regional and global scales), lead isotopic compositions of honey are more useful than metal concentrations in revealing large-scale Pb processes (e.g., the enduring legacy of global leaded gasoline use throughout the twentieth century) and the continental origin of the honey. Lead isotopic compositions of honey collected from N. America (especially from the eastern USA) are more radiogenic ( 206 Pb/ 207 Pb: 1.132-1.253, 208 Pb/ 206 Pb: 2.001-2.129) compared to European honey, and honey from New Zealand, which has the least radiogenic isotopic compositions measured in this study ( 206 Pb/ 207 Pb: 1.077-1.160, 208 Pb/ 206 Pb: 2.090-2.187). Thus, biomonitoring using honey at different resolutions reflects differing processes and, to some extent, a honey terroir defined by the Pb isotopic composition. The data presented here provide important (and current) global context for future studies that utilize Pb isotopes in honey. Moreover, this study exhibits community science in action, as most of the honey was collected by collaborators around the world, working directly with local apiarists and hobby beekeepers., (Copyright © 2021 Elsevier Inc. All rights reserved.)

The article focuses on the controversy regarding the nuclear reactor in Chalk River in Ontario, Canada, which produces the raw materials for medical isotopes. It notes that the controversy has become an international embarrassment for Canada while some European isotope producers has refused to participate in the efforts to coordinate with the international isotope supply. On the other hand, it also reveals that the conflict between the U.S. and the company MDS Nordion is prompting calls for the creation of a domestic supplier which would get the company of its greatest customer. INSET: Securing Canada's isotope supply.

The petrogenesis of the Pridoli to Early Lochkovian granites in the Miramichi Highlands of New Brunswick, Canada, is controversial. This study focuses on the Pridoli Nashwaak Granite (biotite granite and two-mica granite). In situ trace elements and O and Hf isotopes in zircon, coupled with O isotopes in quartz, are used to reveal its magmatic sources and evolution processes. In the biotite granite, inherited zircon cores have broadly homogenous δ18OZrc ranging from +6.7‰ to 7.4‰, whereas magmatic zircon rims have δ18OZrc of +6.3‰ to 7.2‰ and εHf(t) of −0.39 to −5.10. The Hf and Yb/Gd increase with decreasing Th/U. Quartz is isotopically equilibrated with magmatic zircon rims. The biotite granite is interpreted to be solely derived by partial melting of old basement rocks of Ganderia and fractionally crystallized at the fO2 of 10−21 to 10−10 bars. The two-mica granite has heterogeneous inherited zircon cores (δ18OZrc of +5.2‰ to 9.9‰) and rims (δ18OZrc of +6.2‰ to 8.7‰), and εHf(t) of −11.7 to −1.01. The two-mica granite was derived from the same basement, but with supracrustal contamination. This open-system process is also recorded by Yb/Gd and Th/U ratios in zircon and isotopic disequilibrium between magmatic zircon rims and quartz (+10.3 ± 0.2‰). [ABSTRACT FROM AUTHOR]

Little is known about how forests adjust their gas-exchange mode while atmospheric CO 2 rises globally and air quality changes regionally. The present study aims at addressing this research gap for boreal spruce trees growing in three different regions of Canada, submitted to distinct levels of atmospheric emissions, by examining the amount of carbon gained per unit of water lost in trees, i.e., the intrinsic water use efficiency (iWUE). Under pristine air quality conditions, middle-to long-term trends passed from no-reaction mode to passive strategies due to atmospheric CO 2 , and short-term iWUE variations mostly ensue from year-to-year climatic conditions. In contrast, in trees exposed to pollutants from a copper smelter and an oil-sands mining region, air quality deterioration generated swift, long-term iWUE rises immediately at the onset of operations. In this case, the very active foliar strategy sharply reduced the intra-foliar CO 2 (Ci) pressure. Statistical modeling allowed identifying emissions as the main trigger for the iWUE swift shifts; subsequent combined effects of emissions and rising CO 2 led to passive foliar modes in the recent decades, and short-term variations due to climatic conditions appeared all along the series. Overall, boreal trees under different regional conditions modified their foliar strategies mostly without changing their stem growth. These findings underline the potential of acidifying emissions for prompting major iWUE increases due to lowering the stomatal apertures in leaves, and the combined influence of rising CO 2 in modulating other foliar responses. A fallout of this research is that degrading air quality may create true divergences in the relationship between tree-ring isotopes and climatic conditions, an impact to consider prior to using isotopic series for paleo-climatic modeling. Image 1 • IWUE was determined for boreal trees submitted to distinct levels of atmospheric emissions. • Trees from remote stands rise iWUE proportionally with atmospheric pCO 2. • IWUE trends of exposed stands depart from regular pCO 2 -induced reactions. • Trees modified their foliar strategies without changing their stem growth. • Modeling underlines the individual and combined influences of pCO 2 and acidifying pollutants. Gas exchange strategies of forests exposed to acidifying emissions create major divergences from responses to pCO 2 and climatic conditions, a concern for modeling global C and water cycles. [ABSTRACT FROM AUTHOR]

• We present LASS U–Pb and Sm–Nd isotope data from the Acasta Gneiss Complex, Canada. • Sm–Nd redistribution occurred at 3.3 Ga and again during the 1.89 Ga Wopmay orogen. • Sm–Nd redistribution is a common feature of ancient poly-metamorphic terranes. • Sm–Nd mobility may compromise the initial Nd isotope composition of ancient rocks. • Analysis of Nd-rich minerals proves useful for assessing bulk-rock Nd isotope data. The whole rock 143Nd isotope record of the Acasta Gneiss Complex (AGC) has been used to argue for the development of both depleted mantle and enriched crustal reservoirs during the Hadean. The 147Sm–143Nd isotope compositions of rocks from AGC, however, fall on an array with an errorchron date of ∼3.3 Ga, despite the majority of samples yielding substantially older zircon U–Pb ages. This has led to the suggestion of a major Sm–Nd "resetting" event at this time in the AGC. To better understand the Sm–Nd bulk-rock systematics of the AGC, we investigate the U–Pb age and Sm–Nd isotope compositions of apatite and titanite from the AGC, using the laser ablation split stream (LASS) method. Apatite from all samples yield broadly similar U–Pb dates of ∼1.89 to 1.83 Ga, in agreement with resetting during the 1.9 Ga Wopmay orogen. The Sm–Nd isotope compositions of the apatite, however, lie off the WR errorchron and show a high degree of initial Nd isotope heterogeneity. Conversely, titanite Sm–Nd systematics are consistent with the ∼3.3 Ga whole rock errorchron further supporting Sm–Nd modification at ∼3.3 Ga. Taken together, these show that the oldest rocks in the AGC underwent at least two post-crystallization events (at 3.3 and 1.9 Ga) that modified the Sm–Nd isotope system. These results also demonstrate the relative mobility of the Sm–Nd isotope system during orogenic events, which may compromise the ability to determine robust bulk-rock 143Nd isotope signatures. [ABSTRACT FROM AUTHOR]

The fourteenth International Conference on Electromagnetic Isotope Separators and Techniques related to their Applications, EMIS-14, held in Victoria, Canada, was attended by more than 130 participants. As compared to earlier EMIS conferences, EMIS-14 reflected the increasing importance of experimental developments applicable to unstable nuclei. Reports on efficient isotope separation, beam manipulation such as cooling, trapping and acceleration were presented. The theoretical basis for research with exotic beams was put by W. Nazarewicz. He clearly underlined the importance of neutron rich nuclei which cover a large and unexplored region of the nuclear chart. New phenomena such as the separation of proton and neutron matter in nuclei or disappearance and formation of new nuclear shells are expected. The investigation of the rich field of nuclei far-off stability will shed light on the in-medium nucleon–nucleon interaction and finally help to understand the structure of elementary matter. [Copyright &y& Elsevier]

Migratory songbirds breeding in the Canadian Boreal forest are exposed to mercury (Hg), a potent neurotoxin that impairs avian health, however, the degree of exposure depends on many factors. As breeding grounds are geographically remote and vast, the measurement of Hg in individual birds is impractical particularly at large spatial scales. Here, we present a Canada-wide dataset of nearly 2000 migratory songbirds that were used to assess summer Hg exposure of 15 songbird species sampled during fall migration. We measured Hg concentrations in tail feathers and related those to dietary guild, geographic capture location, age, sex and probable breeding ground locations using feather δ 2 H. Overall mean (±SE) feather Hg concentration was 1.49 ± 0.03 μg/g (N = 1946): however, a clear geographic gradient in feather Hg concentrations emerged being highest in East and lowest in West. Dietary guild was the next strongest predictor of feather Hg with insectivorous songbirds in Eastern Canada at particular risk due to Hg exposure on summer breeding grounds. This broad-scale assessment of Hg exposure in migratory songbirds in Canada can be used to guide future studies on finer-scale determinants of Hg exposure in birds., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Mining activities at Duparquet in Western Quebec (Canada) have significantly affected the local environment and left behind significant amounts of metals. Monitoring this contamination is essential to infer its past and present impacts on environmental quality and to evaluate the resulting human exposure. In that context, we measured long time series of Pb concentrations and their corresponding stable isotope ratios in long-lived white cedars (Thuja occidentalis L.) growing at Duparquet Lake in order to evaluate potential time variations of the Pb environmental contamination as well as to identify the responsible source(s). Results show that before 1950, Pb at Duparquet is mostly terrigenous. Lead concentrations rapidly increase afterwards. A simultaneous shift to lower 206 Pb/ 207 Pb ratios identifies the smelting of Abitibi ores as the source of contamination. An isotope mass balance model evaluates at roughly 7.5-20%, 5-40%, 5-9% and <3% the Pb contributions from local smelters at distances of 3.6, 3.9, 7 and 9 km, respectively. The dispersion of the Pb contamination plume is possibly driven by the distance from the Beattie smelter. We finally estimated a delay of at least 13 years between atmospheric emissions from the Beattie smelting activities and the time they are recorded by tree rings. Ultimately, this study demonstrates that white cedar tree rings series provide reliable archives of past and present Pb atmospheric contamination., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Feeding ecology of Atlantic bluefin tuna (ABFT, Thunnus thynnus), from the Gulf of Saint Lawrence, Canada, was assessed by stomach content and stable isotope analyses. Stomachs were collected from 161 individuals averaging 249 ± 20 cm in curved fork length and 248 ± 64 in round weight. The fish were caught by commercial fishing boats using rod and reel gear during fall 2015-2017. Liver and muscle samples were taken from 133 fish for stable isotope analysis. Atlantic mackerel (Scomber scombrus) was the most abundant prey item in 2015 (%Alimentary index, %AI = 88.94), whereas in 2016 and 2017 the ABFT diet was mainly composed of Atlantic herring (Clupea harengus) (%AI = 56.73 and %AI = 77.23, respectively). PERMANOVA analysis revealed significant differences in the dietary composition between years. δ 15 N values varied between 12.3 and 15.4‰ for muscle and between 11.1 and 14.6‰ for liver. δ 13 C values ranged from -19.9 to -16.5‰ for muscle and from -20.7 to -17.3‰ for liver. PERMANOVA analysis also detected inter-annual isotopic differences in both muscle and liver samples (p < 0.05). Daily rations (DR) were similar in 2015 and 2016 (DR = 1.02 ± 0.32 and DR = 1.10 ± 0.21, respectively), but higher in 2017 (DR = 1.73 ± 0.54)., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Ecosystem reconstruction after mining disturbance is a challenge considering the multitude of factors that affect soil formation and revegetation. In the boreal forest of western Canada, peat material is often used as the organic amendment for land reclamation to upland forest. Carbon and water dynamics of peat-dominated ecosystems differ from natural upland forest soils. The objective of this work was to evaluate the evolution of soils reconstructed after mining disturbance using 13 C and 2 H analyses of n-alkane tracers. Ten soils from natural ecosystems were sampled (0-10 cm) and compared with 11 soils from novel ecosystems ranging in age from 0 to 30 yr, as well as a fresh peat sample. Soils supported different vegetation, including pine (Pinus spp.), aspen (Populus spp.), and white spruce [Picea glauca (Moench) Voss]. Despite overlaps for some individual n-alkanes, we found a dominance of n-C 25 in reconstructed soils, also dominant in the peat material, and a dominance of n-C 27 in natural soils, one of the dominant n-alkanes in natural forest vegetation. In addition, there was a significant difference in odd n-alkane δ 2 H and δ 13 C values between natural and reconstructed soils (p < .05). Differences in δ 2 H values, more negative for reconstructed soils than for natural soils, were attributed to changes in soil moisture, from wetter peat-dominated soils to drier upland forests; among forest types, δ 2 H values were most negative under pine vegetation. The δ 13 C composition of odd n-alkanes, in particular n-C 27 , was significantly related to tree age (p < .05). Overall, both 2 H and 13 C isotopic signatures of odd n-alkanes exhibited differences between natural and reconstructed soils. However, within the reconstructed soils, neither isotopic signature showed a clear evolution with age since reclamation., (© 2020 The Authors. Journal of Environmental Quality © 2020 American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America.)