Distinct Isotope Ratios Research Articles

Oxygen isotope study of the Asuka-881020 CH chondrite II: Porphyritic chondrules

Oxygen isotope ratios and elemental compositions of porphyritic chondrules and olivine and pyroxene fragments in the Asuka-881020 CH chondrite were analyzed. The oxygen isotope ratios inside individual porphyritic chondrules are homogeneous within the uncertainty, except for relict grains of olivine and low-Ca pyroxene that have distinct oxygen isotope ratios. The average oxygen isotope ratios of the individual chondrules plot along and above the primitive chondrule mineral (PCM) line with Δ17O (=δ17O – 0.52 × δ18O) values from −4.7 ‰ to +4.1 ‰. The olivine and pyroxene fragments, which have Δ17O values ranging from −2.1 ‰ to +3.2 ‰, are likely to be fragments of the porphyritic chondrules.Unlike the non-porphyritic chondrules in CH and CB chondrites and chondrules in other carbonaceous chondrites, the type I and II chondrules do not show a systematic difference in the Δ17O values. Furthermore, the Δ17O values of the type I chondrules increase from −4.7 ‰ to +4.1 ‰ with increasing Mg# (=molar [MgO]/[MgO + FeO] × 100) from 96 to 99. We argue that the positive Δ17O-Mg# trend is explained by an addition of 16O-poor carbon-rich organics as a reducing agent to the relatively 16O-rich precursor silicate, which is a new environment for chondrule formation. This hypothesis is supported by the two lines of evidence observed in the present study. (1) The chondrules and fragments with higher Δ17O values show larger deviations from the PCM line towards low δ18O, suggesting oxygen isotope mass fractionation between the chondrule melt and CO or CO2. (2) Olivine phenocrysts in the chondrules with high Δ17O values contain Ni-poor Fe-metal particles surrounded by silica-rich glass, which may be reduction products during the chondrule formation. Thus, it is suggested that the porphyritic chondrules in CH and CB chondrites have different origins from chondrules in any other chondrite types, even from the non-porphyritic chondrules in CH and CB chondrites.

Hydrological control of a floodplain subsidy to littoral riverine fish

Ecological subsidies have been hypothesized to be key factors affecting the dynamics of the recipient ecosystems. We assessed the impact of the flood regime on the assimilation of a trophic subsidy produced in the floodplain of a large fluvial lake, Lake Saint-Pierre (Quebec, Canada) on five invertivore littoral fish species (yellow perch (Perca flavescens), pumpkinseed (Lepomis gibbosus), bridle shiner (Notropis bifrenatus), golden shiner (Notemigonus crysoleucas), and banded killifish (Fundulus diaphanus)). We hypothesized that the incorporation of floodplain-derived carbon into fish biomass and individual fitness would increase in years with higher magnitude and longer duration floods. Studying four consecutive years with contrasting spring-flood events, we used a stable isotope mixing model to estimate floodplain contribution, and linear mixed models to analyze the impact of hydrology on floodplain contribution and fish body condition. Floodplain and main river’s invertebrates exhibited statistically distinct isotopic ratios (t test: p value < 0.001). Floodplain contribution and body condition were positively correlated with flooding intensity and duration for all species. Body condition was positively correlated with the assimilation of floodplain-subsidy for golden shiner and banded killifish. Our study identified flooding intensity as a main driver influencing the assimilation of floodplain-derived carbon by littoral fish and their fitness in a large river ecosystem.

Assessing Sedimentary Detrital Pb Isotopes as a Dust Tracer in the Pacific Ocean

AbstractMineral dust particles from different source regions typically have distinct Pb isotope ratios. Theoretically, Pb isotopic composition of terrigenous minerals isolated from open‐ocean sediments should allow for dust provenance reconstructions. However, Pb isotopes of terrigenous fractions of sediments have frequently been inconsistent with expected source region signatures. This study investigates the reason(s) for offsets between the Pb isotope values of the dust component in sediment cores and those expected from source regions with focus on changes in sediment composition, sediment age, and sediment processing for analysis. Pb isotope ratios from Pacific Ocean core‐top sediments show a general delineation of the Intertropical Convergence Zone (ITCZ). Isotope mixing models support these general trends, though similarity in Pb isotope ratios of disparate source regions makes constraining specific sources challenging. Pb isotope ratios in downcore samples varied on glacial/interglacial time scales, being less radiogenic during the last glacial maximum, suggesting either a weakened ITCZ or the addition of a new, less radiogenic, source to the system. Finally, Pb isotope ratios in some source region samples yielded different Pb isotope signatures in bulk source sample than in the insoluble terrigenous fraction of the source sample, indicating that differential mineral preservation within the terrigenous component in sediments may cause offsets from source signatures. Overall, while Pb isotopes show distinct basin‐scale variations, high‐resolution spatial reconstructions require tight age controls and consistency in analytical treatment if used to define ocean sediment source regions.

Changing patterns of habitat use by southern right whales (Eubalaena australis) on their nursery ground at Península Valdés, Argentina, and in their long-range movements

Southern right whales (Eubalaena australis) have been studied on their nursery ground at Península Valdés, Argentina, every year since 1970. Since 1990, 1,208 individuals have been identified from photographs taken during annual aerial surveys; 618 whales were seen in two or more years. Patterns of habitat use have changed during the study in ways which suggest that right whales may be capable of substantial behavioral and ecological flexibility. One male and three females from Península Valdés have been sighted on other nursery grounds (Tristan da Cunha and southern Brazil). Three individuals from Península Valdés were sighted on feeding grounds off Shag Rocks and South Georgia. Some right whales from Península Valdés showed carbon and nitrogen isotope ratios very similar to those seen in right whales off South Africa, while others showed distinctive isotope ratios indicating that they fed in a different area. Whales of all ages and both sexes moved frequently between three major regions of concentration on the Península Valdés nursery ground. Subadults and adult females with calves were resighted at higher rates than adult males and females in non-calf years. Changes in the geographic distribution of whales at the Península include: (1) abandonment of a major region of concentration; (2) establishment of a nursery area adjacent to thecentre of a growing whalewatching industry; and (3) small-scale shifts in distribution, possibly in response to natural and human disturbances.

Spectroscopy of P30 and the abundance of Si29 in presolar grains

The astrophysical $^{29}\mathrm{Si}(p,\ensuremath{\gamma}$) reaction is expected to play a key role in determining the final $^{29}\mathrm{Si}$ yields ejected in nova explosions. Such yields are used to accurately identify the stellar origins of meteoritic stardust and recently, distinctive silicon isotopic ratios have been extracted from a number of presolar grains. Here, the light-ion $^{28}\mathrm{Si}(^{3}\mathrm{He},p$) fusion-evaporation reaction was used to populate low-spin proton-unbound excited states in the nucleus $^{30}\mathrm{P}$ that govern the rate of the astrophysical $^{29}\mathrm{Si}(p,\ensuremath{\gamma}$) reaction. In particular, $\ensuremath{\gamma}$ decays were observed from resonances up to ${E}_{r}=500\phantom{\rule{0.28em}{0ex}}\mathrm{keV}$, and key resonances at 217 and 315 keV have now been identified as ${2}^{+}$ and ${2}^{\ensuremath{-}}$ levels, respectively. The present paper provides the first estimate of the 217-keV resonance strength and indicates that the strength of the 315-keV resonance, which dominates the rate of the $^{29}\mathrm{Si}(p,\ensuremath{\gamma}$) reaction over the entire peak temperature range of oxygen-neon novae, is higher than previously expected. As such, the abundance of $^{29}\mathrm{Si}$ ejected during nova explosions is likely to be less than that predicted by the most recent theoretical models.

Trace elemental and sulfur-lead isotopic variations in metamorphosed volcanogenic massive sulfide (VMS) mineralization systems: An example from the Keketale Pb-Zn(-Ag) deposit, NW China

The effects of post-VMS (volcanogenic massive sulfide) deformation/metamorphism on sulfide trace element and sulfur-lead isotopic compositions remain unclear. The greenschist to lower amphibolite facies metamorphosed Keketale VMS Pb-Zn(-Ag) deposit, located in the Devonian Maizi volcanic-sedimentary basin in the Chinese Altay, NW China, provides an opportunity to resolve the abovementioned issue. Two mineralization stages are recognized at Keketale, including (1) primary banded, massive and disseminated ores derived from sea-floor hydrothermal mineralization and (2) ore remobilization, as represented by intensively-deformed ores and quartz-polymetallic sulfide ore veins that crosscut the primary ores. Sulfide trace elements data suggest that Stage II pyrite and pyrrhotite have higher contents of Cu, Zn, Ag, Sb and Pb, whereas contents of these elements are higher in Stage I sphalerite and galena than their Stage II counterparts. Such elemental remobilization was probably caused by the rapid intragrain diffusion and subsequent fluid-mediated liberation with trace elements re-precipitated as particles within the same grain and nearby minerals, respectively. The δ34SCDT values in both stages show a trimodal distribution (−25.9 to −22.7‰, −17.0 to −10.6‰ and 0.6 to 2.1‰). Sulfide mineral pairs formed during primary VMS mineralization are not in sulfur isotopic equilibrium, and only localized re-equilibration occurs during deformation and metamorphism. In addition, the lead isotopic values of galena from remobilized sulfide veins overlap with those of the Stage I galena and pyrite. These data indicate that regional deformation and metamorphism of the Keketale deposit can be approximated as a closed system in terms of sulfur-lead isotopes. Whilst the presence of the anomalously low δ34S values (minimum −25.9‰) and the distinct lead isotopic ratios of sulfides from the calcite-quartz veins argue for that in the late part of the metamorphic event, some exotic lead and light sulfur were sourced from outside the ore field. In situ δ34S values of Stage I sulfides vary widely (−17.0 to +2.1‰), suggesting that the sulfur was originated from bacterial sulfate reduction (BSR) of marine sulfates with probably some magmatic input. Lead isotopes of the sulfides and mineralized meta-sedimentary-volcanic rocks display a linear distribution between the mantle and upper crust line in the 206Pb/204Pb vs. 207Pb/204Pb diagram. The lead source may be derived from both felsic volcanic rocks and mafic igneous rocks (and/or magmatic volatiles), and the sulfur-lead isotopes may result from a shallow-level seawater circulating process. An additional group of lead isotopic compositions of the meta-volcanic rocks show elevated present-day 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb values, probably due to decay of Th and U carried by deeply-penetrative circulation (~13 km) of CO2-F-Cl-rich hydrothermal (metamorphic) fluids. Both syn-VMS shallow (seawater) and post-VMS deep (metamorphic fluids) circulation processes are critical for the metal concentration at Keketale.

Dynamics of a chemically pulsing mantle plume

Upwelling plumes from the deep mantle have an impact on the Earth's surface for tens to hundreds of millions of years. During the lifetime of a mantle plume, periodic fluctuations in its composition and temperature have the potential to generate changes in the nature and volume of surface volcanism. We constrain the spatial and temporal scale of compositional changes in a plume using high-resolution Pb isotopes, which identify chemical pulses emerging from the Canary Islands hotspot over the last ∼15 million years (Myr). Surface volcanism spanning ∼ 400 km along the island chain changes composition systematically and synchronously, representing a replenishment of the plume head by a distinct mantle flavour on timescales of 3-5 Myr. These low-frequency compositional changes are also recorded by individual volcanoes, and comprise a sequence of closely-spaced isotopic trajectories. Each trajectory is maintained for ∼1 Myr and is preceded and followed by ∼0.3 Myr transitions to magmas with distinct isotope ratios. Relatively sharp transitions between periods of sustained isotopic stability require discrete yet coherent heterogeneities rising at speeds of ∼100-200 kmMyr−1 and extending for ∼150 km vertically in the conduit. The long-term synchronous changes require larger scale isotopic domains extending ∼600 km vertically through in the plume stem. These observations demonstrate that plumes can chemically “pulse” over short and long-timescales reflecting the characteristics and recycling history of the deep mantle.

Sources of Blood Lead Exposure in Rural Bangladesh.

Lead (Pb) exposure is a major public health problem worldwide. Although high levels of Pb in blood in Bangladesh have been documented, the dominant Pb sources contributing to human exposure in rural Bangladesh have not been determined. Here, we first obtained blood from pregnant women from three rural Bangladeshi districts who were previously assessed by a case-control and sampling study, and we then conducted semistructured in-depth interviews to understand Pb exposure behavior and finally collected samples of the suspected Pb sources. We measured the Pb isotopic composition of both potential Pb sources and 45 blood samples in order to understand which of three sources predominate: (1) food from Pb-soldered cans, (2) turmeric, or (3) geophagous materials (clay, soil, or ash). The Pb isotope ratios of the three sources are distinct (p = 0.0001) and blood isotope ratios are most similar to turmeric. Elevated lead and chromium (Cr) concentrations in turmeric and a yellow pigment used in turmeric processing are consistent with reported consumption behavior that indicated turmeric as a primary contributor to blood Pb. The Pb isotopic composition analyses combined with a case-control and sampling approach provides evidence that turmeric adulterated with the yellow Pb-bearing pigment is the main Pb exposure source in these districts and illustrates the need to assess drivers and practices of turmeric adulteration, as well as the prevalence of adulteration across South Asia.

The ups & downs of Iron Age animal management on the Oxfordshire Ridgeway, south-central England: A multi-isotope approach

The hillforts of the Oxfordshire Ridgeway in south-central England have been interpreted as central places in the Early/Middle Iron Age, ca. 600–100 BCE, serving, among other functions, to integrate the management of animals, particularly sheep, between the upland Chalk downs and the adjacent low-lying Vale of the White Horse. Since these landforms differ geologically and pedologically, they lead to distinct isotopic ratios in the biosphere and so present the potential to investigate animal management practices in some detail. Here, we report the results of a multi-isotope study on domestic fauna (cattle, sheep and pig) within a very constrained study area, with the aim of testing the hypothesis that the Ridgeway's hillforts were placed to control and coordinate the movement of sheep between the Chalk and the Vale. However, the results suggest a different scenario. Bone collagen δ15N results indicate that cattle and sheep were both kept locally. Strontium isotopes, conversely, indicate that, while sheep and pigs were raised locally, cattle appear to have been mainly kept in the Vale during at least the first year of their lives. The apparent discrepancy between the two isotopes can be reconciled by the different periods of life represented by enamel and bone collagen measurements, with the movement of cattle onto the Ridgeway in their second or third year of life. Sequential measurements of δ13C and δ15N in dentine, and of δ13Cc and δ18Oc in enamel, provide further detail on the management of cattle, and offer some support for the above scenario. Early/Middle Iron Age stock-keeping in south-central England was complex, being integrated in some respects but distinct in others. The study demonstrates the level of detail it is possible to achieve with a multi-isotope approach to animal management practices in prehistory. The focus on a micro-region contrasts with, or rather complements, studies addressing larger-scale movement of animals in the past.

A study of the glazing techniques and provenances of Tang sancai glazes using elemental and lead isotope analyses

This study discusses the elemental compositions and lead isotope ratios of Tang sancai glazes unearthed from the Huangpu kiln, Huangye kiln and two Tang sancai tomb sites. The various glazes feature distinct lead isotope ratios and trace element characteristics, which can be interpreted as evidence for the use of different lead ore deposits and siliceous raw materials in the glazes. This is a strong indication that lead isotopes combined with trace element analysis could be used as a viable approach for identifying the provenance of Tang sancai of unknown origin by linking them to kiln sites, This provenance technique could be significant in the interpretation of ancient ceramic trade and communication patterns. In this study, the provenance of several Tang sancai glazes of uncertain origin were determined using this method: some Tang sancai wares unearthed in Xi'an City were produced in the kiln near Luoyang City and then traded to Xi'an City, providing an idea of ancient Tang sancai ceramic trade routes.

Distribution of inositol phosphates in animal feed grains and excreta: distinctions among isomers and phosphate oxygen isotope compositions

Phytate (myo-IP6) is a common form of organic phosphorus in the environment. Little information is available, however, about the distribution of phytate and its degradation products. In this research, we aimed to identify the compositions of phytate in different natural P sources as well as to explore a reliable method to measure their isotope signatures so that the link between original phytate and P outputs in the environment could be established. A variety of feed ingredients for selected ruminant and non-ruminant animals and their excreta were analyzed using HPIC (high-performance ion chromatography) and their oxygen isotope (δ18OPA-Pi) signatures were identified using IRMS (isotope ratio mass spectrometry) method. The HPIC results show that IP6 was dominant in all grains, followed by IP5 and several IP4 isomers, and an insignificant amount of IP3. Similarly, IP6 and IP5 were also detected in all animal feeds and several excreta. More importantly, the distribution of different IPx species in a grain type was essentially the same. The δ18OPA values of phytate in grains varied from 20.5 to 24.2 ‰, while the δ18OPi values of inorganic P in the same grains were heavier by 0.4-3.2‰. Similarly, the δ18OPA values of phytate in animal feeds and excreta were within the ranges of grain phytate. Overall, combination of results from IRMS and HPIC analyses provided important information on the distribution of IPx species in various sources and their distinct oxygen isotope ratios pointed towards the possibility of connecting the original phytate sources to degradation products in the environment.

Non-Vestoid candidate asteroids in the inner main belt

Most Howardite-Eucrite-Diogenite (HED) meteorites (analogs to V-type asteroids) are thought to originate from asteroid (4) Vesta. However, some HEDs show distinct oxygen isotope ratios and therefore are thought to originate from other asteroids. In this study, we try to identify asteroids that may represent parent bodies of those mismatching HEDs. In particular, the origin of the anomalous Bunburra Rockhole meteorite was traced back to the inner main asteroid belt, showing that there might be asteroids that are not genetically linked to the asteroid (4) Vesta (the main source of V-type asteroids and HED meteorites) in the inner main belt. In this work we identify V-type asteroids outside the dynamical Vesta family whose rotational properties (retrograde vs prograde rotation) suggest the direction of Yarkovsky drift that sets them apart from typical Vestoids and Vesta fugitives. Specifically Nesvorny et al. 2008 simulated escapes paths from the Vesta family and showed that typical Vesta fugitives in the inner main asteroid belt at semi-major axis a < 2.3 AU have to have retrograde rotations and physical and thermal parameters that maximize the Yarkovsky force in order to evolve to scattered orbits within 1-2 Gyrs (age of the Vesta collisional family). Therefore large asteroids outside the Vesta family and with a < 2.3 AU and having thermal and rotational properties minimizing the Yarkovsky drift or showing Yarkovsky drift direction towards (4) Vesta are the best candidates for non-Vestoids V-type asteroids and therefore parent bodies of anomalous HED. In this study, we have performed accurate photometric observations and determined sense of rotation for several asteroids testing their links to Vesta and anomalous HED. We have found several potential non-Vestoid candidates. Those objects have to be studied in more detail to fully confirm their link to anomalous HEDs.

Lead (Pb) Isotope Baselines for Studies of Ancient Human Migration and Trade in the Maya Region.

We examined the potential use of lead (Pb) isotopes to source archaeological materials from the Maya region of Mesoamerica. The main objectives were to determine if: 1) geologic terrains throughout the Maya area exhibit distinct lead isotope ratios (206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb), and 2) a combination of lead and strontium ratios can enhance sourcing procedures in the Mesoamerica region. We analyzed 60 rock samples for lead isotope ratios and a representative subset of samples for lead, uranium, and thorium concentrations across the Maya region, including the Northern Lowlands of the Mexican Yucatan Peninsula, the Southern Lowlands of Guatemala and Belize, the Volcanic Highlands, the Belizean Maya Mountains, and the Metamorphic Province/Motagua Valley. Although there is some overlap within certain sub-regions, particularly the geologically diverse Metamorphic Province, lead isotopes can be used to distinguish between the Northern Lowlands, the Southern Lowlands, and the Volcanic Highlands. The distinct lead isotope ratios in the sub-regions are related to the geology of the Maya area, exhibiting a general trend in the lowlands of geologically younger rocks in the north to older rocks in the south, and Cenozoic volcanic rocks in the southern highlands. Combined with other sourcing techniques such as strontium (87Sr/86Sr) and oxygen (δ18O), a regional baseline for lead isotope ratios can contribute to the development of lead isoscapes in the Maya area, and may help to distinguish among geographic sub-regions at a finer scale than has been previously possible. These isotope baselines will provide archaeologists with an additional tool to track the origin and movement of ancient humans and artifacts across this important region.

Identification of anthropogenic and natural inputs of sulfate into a karstic coastal groundwater system in northeast China: evidence from major ions, &amp;lt;i&amp;gt;δ&amp;lt;/i&amp;gt;&amp;lt;sup&amp;gt;13&amp;lt;/sup&amp;gt;C&amp;lt;sub&amp;gt;DIC&amp;lt;/sub&amp;gt; and &amp;lt;i&amp;gt;δ&amp;lt;/i&amp;gt;&amp;lt;sup&amp;gt;34&amp;lt;/sup&amp;gt;S&amp;lt;sub&amp;gt;SO&amp;lt;sub&amp;gt;4&amp;lt;/sub&amp;gt;&amp;lt;/sub&amp;gt;

Abstract. The hydrogeochemical processes controlling groundwater evolution in the Daweijia area of Dalian, northeast China, were characterised using hydrochemistry and isotopes of carbon and sulfur (δ13CDIC and δ34SSO4). The aim was to distinguish anthropogenic impacts as distinct from natural processes, with a particular focus on sulfate, which is found at elevated levels (range: 54.4 to 368.8 mg L−1; mean: 174.4 mg L−1) in fresh and brackish groundwater. The current investigation reveals minor seawater intrusion impact (not exceeding 5 % of the overall solute load), in contrast with extensive impacts observed in 1982 during the height of intensive abstraction. This indicates that measures to restrict groundwater abstraction have been effective. However, hydrochemical facies analysis shows that the groundwater remains in a state of ongoing hydrochemical evolution (towards Ca–Cl type water) and quality degradation (increasing nitrate and sulfate concentrations). The wide range of NO3 concentrations (74.7–579 mg L−1) in the Quaternary aquifer indicates considerable input of fertilisers and/or leakage from septic systems. Both δ13C (−14.5 to −5.9 ‰) and δ34SSO4 (+5.4 to +13.1 ‰) values in groundwater show increasing trends along groundwater flow paths. While carbonate minerals may contribute to increasing δ13CDIC and δ34SSO4 values in deep karstic groundwater, high loads of agricultural fertilisers reaching the aquifer via irrigation return flow are likely the main source of the dissolved sulfate in Quaternary groundwater, as shown by distinctive isotopic ratios and a lack of evidence for other sources in the major ion chemistry. According to isotope mass balance calculations, the fertiliser contribution to overall sulfate has reached an average of 62.1 % in the Quaternary aquifer, which has a strong hydraulic connection to the underlying carbonate aquifer. The results point to an alarming level of impact from the local intensive agriculture on the groundwater system, a widespread problem throughout China.

The geochemical components that distinguish Loa- and Kea-trend Hawaiian shield lavas

Recent (<5Ma) Hawaiian volcanoes define two sub-parallel spatial trends, Loa and Kea. Despite the short distance (∼30km) between adjacent volcanoes on these trends, most of the Loa-trend shield lavas are geochemically distinct from most of the Kea-trend shield lavas. These geochemical differences arise from small amounts of the LOA component in the source of Loa-trend shield lavas. This component is most prominent in the uppermost shield lavas of Koolau, Lanai and Kahoolawe volcanoes. Correlations between abundance ratios of incompatible elements and isotopic ratios of Sr, Nd, Hf and Pb in Hawaiian shield lavas indicate that the LOA component consists of three geochemically distinct materials formed by diverse processes. A gabbroic adcumulate (i.e. no trapped melt) with abundant cumulus plagioclase is responsible for the high Sr/Nd, La/Th and La/Nb in Loa-trend shield lavas relative to Kea-trend shield lavas. Also it has relatively low 206Pb/204Pb and high 208Pb/204Pb at a given 206Pb/204Pb, consistent with the low U/Pb and Th/Pb that are characteristic of plagioclase; these distinctive Pb isotope ratios require a long-time interval, ∼3Ga, to develop. This material is most abundant in the uppermost shield lavas of Koolau volcano. Possible origins of adcumulate gabbros with abundant cumulus plagioclase are the lower oceanic and continental crust. A second material in the LOA component is distinctive because it is offset from the linear trend of 176Hf/177Hf versus 143Nd/144Nd, known as the terrestrial array, to high 176Hf/177Hf at low 143Nd/144Nd. This offset requires an ancient material with high Lu/Hf. It is equally abundant in the shield lavas at Koolau, Lanai and Kahoolawe volcanoes. Possible origins of this material are ancient pelagic sediment or ancient depleted lithosphere. A third material in the LOA component is characterized by relatively high 87Sr/86Sr, but the Rb/Sr of this material is too low to explain the high 87Sr/86Sr in 4.5Ga. A relatively recent (<1Ga) event must have lowered the Rb/Sr. This material is most abundant in the shield lavas of Kahoolawe volcano.

Connectivity within estuaries: An otolith chemistry and muscle stable isotope approach

Understanding whether fish move among estuarine areas and habitats or show high site fidelity has major implications for habitat conservation and the safeguard of estuarine ecological integrity. Muscle stable isotopes (δ13C, δ15N) and otolith elemental composition (Li:Ca, Mg:Ca, Mn:Ca, Cu:Ca, Sr:Ca, Ba:Ca and Pb:Ca) were used to evaluate connectivity between two separate estuarine nursery areas in summer and autumn for juvenile age-0 Dicentrarchus labrax and Pomatoschistus microps. Distinct isotopic ratios and otolith elemental signatures were found between areas for D. labrax and P. microps, and in both sampling times. High classification accuracies to collection sites were achieved via otolith elemental signatures (80–94%), and a combined analysis using both muscle stable isotopes and otolith chemistry resulted in increased accuracy with no classification errors. Overall, low site connectivity was found for both species. The use of two distinct natural tags provided corroborative and complementary information on fish movement and intra-estuarine habitat use at different temporal scales, whilst elucidating distinct ecological and environmental linkages. Ultimately, the combined use of distinct natural tags showed great promise to unravel intra-estuarine connectivity patterns.

Geochemistry, Sr–Nd–Pb isotopes and geochronology of amphibole- and mica-bearing lamprophyres in northwestern Iran: Implications for mantle wedge heterogeneity in a palaeo-subduction zone

Highlights • Northwestern Iranian lamprophyres have alkaline and calc-alkaline nature. • Studied lamprophyres are emplaced during Late Cretaceous to Late Miocene time. • Lamprophyres originated from different metasomatised lithospheric mantle. Abstract Lamprophyres of different age showing distinctive mineralogy, geochemistry and isotopic ratios are exposed in northwestern Iran. They can be divided into Late Cretaceous sannaite, Late Oligocene-Early Miocene camptonite (amphibole-bearing) and Late Miocene minette (mica-bearing) and spessartite (amphibole-bearing) lamprophyres. Sannaites have high-Ti amphibole along with high-Ti and Al clinopyroxene, and they are characterised by homogeneous enrichment in incompatible trace elements with troughs at Pb. Spessartites have hornblende and low-Al and Ti clinopyroxene, and they are characterised by enriched incompatible trace element pattern with depletions of Nb, Ta, Pb, and Ti with respect to large ion lithophile elements. Minettes have high-Ti and Al brown mica and low-Al and Ti clinopyroxene, and similarly to spessartite, are characterised by fractionation of high field strength elements with respect to large ion lithophile elements, with troughs at Nb, Ta, and Ti and a peak at Pb. Minettes show high initial 87Sr/86Sr values up to 0.70760 and low initial 143Nd/144Nd down to 0.512463 with a negative correlation, consistent with the trace element distribution related with an enriched mantle source modified after sediment recycling during subduction and continental collision. Cretaceous sannaites and Early Miocene spessartites show low initial 87Sr/86Sr approaching 0.70447 and high 143Nd/144Nd values up to 0.512667, which are consistent with a depleted within-plate mantle source. Minette and spessartite lamprophyres show high initial 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb values, whereas sannaites have lower, but variable, initial 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb values with respect to those of calc-alkaline lamprophyres. Minettes originated by partial melting of a metasomatised lithospheric mantle following siliciclastic sediment recycling by subduction. In contrast, sannaites were generated from the partial melting of a similar lithospheric mantle that was metasomatised by within-plate agents.

Dynamic variability of dissolved Pb and Pb isotope composition from the U.S. North Atlantic GEOTRACES transect

This study presents dissolved Pb concentration and isotopic composition distributions from GEOTRACES GA03, the U.S. North Atlantic Transect. Pb in the ocean is primarily derived from anthropogenic sources and Pb fluxes into the North Atlantic Ocean have been steadily decreasing following the phase-out of alkyl leaded gasoline usage in North America and Europe between 1975 and 1995. A compilation of dissolved Pb profiles from three stations occupied repeatedly during the last three decades reveals a dramatic decrease in concentrations within the surface layers and the thermocline maxima, although elevated concentrations greater than 60pmol/kg are still observed in the center of the North Atlantic gyre where ventilation timescales are longer than at the western boundary. The evolution of stable Pb isotopes at these stations shows a shift from dominantly North American-like composition in surface waters in the early 1980s towards a more European-like composition in later years. The most recent shallow signatures at the Bermuda Atlantic Time Series station (BATS) show an even more recent trend returning to higher 206Pb/207Pb ratios after the completed phase-out of leaded gasoline in Europe, presumably because recently deposited Pb is more strongly influenced by industrial and incineration Pb than by residual alkyl leaded gasoline utilization. In surface waters, trends toward a more prominent European influence are also found in the middle of the basin and toward the European coast, coincident with higher concentrations of surface dissolved Pb. Scavenging of anthropogenic Pb is observed within the TAG hydrothermal plume, and it is unclear if there is any significant contribution to deep water by basaltic Pb leached by hydrothermal fluids. In the upper water column, many stations along the transect show Pb concentration maxima at ~100m depth, coincident with a low 206Pb/207Pb isotopic signature that is typical of European emission sources. Although Pb ores from the United States historically tend to carry 206Pb/207Pb signatures >1.17 (Hurst, 2002), subsurface signatures as low as 1.1563 in 206Pb/207Pb were observed in this feature. This signature appears to be carried westward within saline Subtropical Underwater (STUW), that ventilates from the Central Eastern part of the North Atlantic Subtropical Gyre where the lowest surface isotope 206Pb/207Pb ratios are observed. Along the western boundary, deep water masses of different ages carry distinct isotope ratios corresponding to their respective times of ventilation. Finally, a low 206Pb/207Pb signature in bottom water along the Eastern margin suggests that there may be some mobilization of European-derived anthropogenic Pb from recent surface deposits on the ocean floor.

Element Cycling in the Critical Zone as Viewed by New Isotope Tools

Isotope Geochemists are dedicating substantial effort at developing isotope ratio-based tools that are now beginning to provide detailed insights into the processes that cycle elements between the compartments of the weathering zone. The first group makes use of the metal and metalloid elements of which the stable isotope ratios shift mainly when a) secondary minerals are formed; b) elements are cycled through higher plants. Distinct stable isotope ratios emerge for a given cycled element as a function of the isotope fractionation factor of the process involved and of the elements’ relative fluxes through these compartments (e.g. soil water, secondary minerals, plants, remaining primary minerals). A second tool provides absolute fluxes from the weathering zone: The ratio of the meteoric cosmogenic nuclide 10Be (T1/2 = 1.39 My) to the stable isotope 9Be combines a tracer of roughly known flux to the Earth's surface (over time scales characteristic of weathering) with one that depends on its release rate from rock by weathering. The resulting 10Be/9Be isotope ratio discloses both the Earth surfaces’ denudation rate and its weathering intensity. For both tools, a set of steady state mass balance equations describe these systems from the scale of a soil column over the hillslope scale to an entire river basin.

The sub-Antarctic Antipodes Volcano: a

The sub-Antarctic Antipodes Islands group, located on the edge of the Campbell Plateau, is composed of Surtseyan-like tuff cones, porphyritic lavas and dykes, overlain by scoriaceous cinder cones. The youthful nature is indicated by well-preserved cones and craters, raised boulder beaches, pollen and spores comparable to the present-day vegetation in peat underlying one lava flow, and published Ar/Ar ages of ≤0.5 Ma. The alkaline crystalline rocks record a fractionation lineage that was controlled by progressive removal of clinopyroxene and olivine at shallow depths with minimal interaction with continental crust. A compilation of isotopic data confirms that the magmas were derived from a mantle source containing a high-time integrated U/Pb (HIMU)-like component. Although this source component has been recognised in many Zealandia intraplate volcanoes, the Antipodes Volcano lavas contain consistently high 206Pb/204Pb and low 87Sr/86Sr ratios, making the geochemical suite an excellent baseline for HIMU studies. The distinctive isotope ratios and chemistries are comparable with those of some anhydrous Pb- and K-depleted peridotitic mantle xenoliths from intraplate volcanoes in Zealandia. If the lithospheric mantle contributed to the source of Antipodes Volcano, the Pb and K anomalies in the lavas may not require residual amphibole/phlogopite and/or sulphide in their source region. Furthermore, comparison with the peridotite suite indicates that the Zealandia lithospheric mantle is isotopically heterogeneous and thus not all the Zealandia Cretaceous–Cenozoic intraplate volcanoes need have tapped a HIMU-like reservoir.