Century-long record of Mo isotopic composition in sediments of a seasonally anoxic estuary (Chesapeake Bay)

A double-spike method was used to obtain Mo isotope data for sediments and waters of the seasonally anoxic Chesapeake Bay, and its primary tributary, the Susquehanna River. The dissolved Mo distribution in the estuary is non-conservative, reflecting minor Mo loss to the sediments, although removal of Mo to the sediments does not have a large influence on the isotopic composition of the water column. The δ⁹⁸Mo of dissolved Mo in most of the estuary is dominated by seawater. Six samples with salinity > 15 have an average δ⁹⁸Mo = + 2.17‰ (± 0.12), which agrees well with a δ⁹⁸Mo value for the CASS-4 seawater standard of + 2.23‰. A single sample of Susquehanna River water has a δ⁹⁸Mo of + 1.02‰, consistent with recent findings of positive δ⁹⁸Mo in rivers worldwide. Susquehanna river sediments, in contrast, have δ⁹⁸Mo ～ ? 0.1‰. The difference between the river water and sediment values implies that isotopic fractionation occurs within the river basin. The δ⁹⁸Mo values for estuarine sediments are offset from values in the overlying water. Most samples deposited before 1925 have δ⁹⁸Mo less than 0‰, similar to the Susquehanna sediments. Subsequently, there is an increase in the variability of δ⁹⁸Mo, with values ranging up to + 0.8‰. The transition to increased variability coincides with the onset of authigenic Mo deposition, which was previously attributed to escalating summertime anoxia. Authigenic Mo concentrations correlate poorly with δ⁹⁸Mo in core samples, suggesting that independent mechanisms influence the two parameters. Authigenic Mo concentrations may be controlled by shifting pore water H₂S levels, while δ⁹⁸Mo may be primarily affected by annual variations in Mn refluxing.     

Oxygen isotope constraints on the origin and differentiation of the Moon

We report new high-precision laser fluorination three-isotope oxygen data for lunar materials. Terrestrial silicates with a range of δ¹⁸O values (− 0.5 to 22.9‰) were analyzed to independently determine the slope of the terrestrial fractionation line (TFL; λ = 0.5259 ± 0.0008; 95% confidence level). This new TFL determination allows direct comparison of lunar oxygen isotope systematics with those of Earth. Values of Δ¹⁷O for Apollo 12, 15, and 17 basalts and Luna 24 soil samples average 0.01‰ and are indistinguishable from the TFL. The δ¹⁸O values of high- and low-Ti lunar basalts are distinct. Average whole-rock δ¹⁸O values for low-Ti lunar basalts from the Apollo 12 (5.72 ± 0.06‰) and Apollo 15 landing sites (5.65 ± 0.12‰) are identical within error and are markedly higher than Apollo 17 high-Ti basalts (5.46 ± 0.11‰). Evolved low-Ti LaPaz mare-basalt meteorite δ¹⁸O values (5.67 ± 0.05‰) are in close agreement with more primitive low-Ti Apollo 12 and 15 mare basalts. Modeling of lunar mare-basalt source composition indicates that the high- and low-Ti mare-basalt mantle reservoirs were in oxygen isotope equilibrium and that variations in δ¹⁸O do not result from fractional crystallization. Instead, these differences are consistent with mineralogically heterogeneous mantle sources for mare basalts, and with lunar magma ocean differentiation models that result in a thick feldspathic crust, an olivine–pyroxene-rich mantle, and late-stage ilmenite-rich zones that were convectively mixed into deeper portions of the lunar mantle. Higher average δ¹⁸O (WR) values of low-Ti basalts compared to terrestrial mid ocean ridge basalts (Δ=0.18‰) suggest a possible oxygen isotopic difference between the terrestrial and lunar mantles. However, calculations of the δ¹⁸O of lunar mantle olivine in this study are only 0.05‰ higher than terrestrial mantle olivine. These observations may have important implications for understanding the formation of the Earth–Moon system.     

Magnesium isotopes constraints on the origin of Mg-rich olivines from the Allende chondrite: Nebular versus planetary?

High precision Mg isotope measurements by multi-collector ion microprobe show that refractory olivines from the Allende chondrite, either olivines isolated in the matrix (2 samples studied) or olivines in type I chondrules (6 samples studied), have variable δ²⁶Mg* enrichments and deficits (calculated in permil as the ²⁶Mg deviation from the instrumental mass fractionation line) relative to the Earth. Most average δ²⁶Mg* (noted δ²⁶Mg*_av) values (between 10 and 20 analyses per chondrule) are negative but the total range is from ?0.029 (± 0.010) ‰ (2 sigma errors) to + 0.011 (± 0.011) ‰ with an exception of one olivine at + 0.043 (± 0.023) ‰. These variations in δ²⁶Mg*_av reflect the formation of the olivines from reservoirs enriched in various amounts of ²⁶Mg by the decay of short-lived ²⁶Al (T_1/2 = 0.73 Ma). Similarly, 30 analyses of olivines from the Eagle Station pallasite show a δ²⁶Mg*_av value of ?0.033 ± 0.008‰, as negative as some olivines from Allende chondrules and the Solar system initial δ²⁶Mg* value of ?0.038 ± 0.004‰ (defined at the time of formation of type B Ca–Al-rich inclusions – CAIs – when ²⁶Al/²⁷Al = 5.23 × 10^?5, Jacobsen et al., 2008).Because olivines are Al-poor and because their Mg isotopic compositions are not reset during the chondrule forming events, their δ²⁶Mg*_av can be used to calculate model crystallization ages relative to various theoretical Mg isotope growth curves. The two end-member scenarios considered are (i) a “nebular” growth in which the Al/Mg ratio remains chondritic and (ii) a “planetary” growth in which a significant increase of the Al/Mg ratio can be due to, for instance, olivine magmatic fractionation. The low δ²⁶Mg*_av value of olivines from the Eagle Station pallasite demonstrate that metal-silicate differentiation occurred as early as ~ 0. 15_- 0. 23^+ 0. 29 Ma after CAIs in either of the growth scenarios. Similarly the variable δ²⁶Mg*_av values of refractory olivines can be understood if they were formed in planetesimals which started to differentiate as early as the Eagle Station parent body. Accretion of these planetesimals must have been coeval to the formation of CAIs and their disruption could explain why their fragments (Mg-rich olivines) were distributed in the chondrule forming regions of the disk.     

Coupled silicon–oxygen isotope fractionation traces Archaean silicification

Silica alteration zones and cherts are a conspicuous feature of Archaean greenstone belts worldwide and provide evidence of extensive mobilisation of silica in the marine environment of the early Earth. In order to understand the process(es) of silicification we measured the silicon and oxygen isotope composition of sections of variably silicified basalts and overlying bedded cherts from the Theespruit, Hooggenoeg and Kromberg Formations of the Barberton Greenstone Belt, South Africa.The δ³⁰Si and δ¹⁸O values of bulk rock increase with increasing amount of silicification from unsilicified basalts (?0.64‰ < δ³⁰Si < ?0.01‰ and + 8.6‰ < δ¹⁸O < + 11.9‰) to silicified basalts (δ³⁰Si and δ¹⁸O values as high as + 0.81‰ and + 15.6‰, respectively). Cherts generally have positive isotope ratios (+ 0.21‰ < δ³⁰Si < + 1.05‰ and + 10.9 < δ¹⁸O < + 17.1), except two cherts, which have negative δ³⁰Si values, but high δ¹⁸O (up to + 19.5‰).The pronounced positive correlations between δ³⁰Si, δ¹⁸O and SiO₂ imply that the isotope variation is driven by the silicification process which coevally introduced both ¹⁸O and ³⁰Si into the basalts. The oxygen isotope variation in the basalts from about 8.6‰ to 15.6‰ is likely to represent temperature-dependent isotope fractionation during alteration. Our proposed model for the observed silicon isotope variation relies on a temperature-controlled basalt dissolution vs. silica deposition process.     

Tracking the lithium isotopic evolution of the mantle using carbonatites

Carbonatites are mantle-derived, intraplate magmas that provide a means of documenting isotopic variations of the Earth's mantle through time. To investigate the secular Li isotopic evolution of the mantle and to test whether Li isotopes document systematic recycling of material processed at or near the Earth's surface into the mantle, we analyzed the Li isotopic compositions of carbonatites and spatially associated mafic silicate rocks. The Li isotopic compositions of Archean (2.7 Ga) to Recent carbonatites (δ⁷Li = 4.1 ± 1.3 (n = 23, 1σ)) overlap the range typical for modern mantle-derived rocks, and do not change with time, despite ongoing crustal recycling. Thus, the average Li isotopic composition of recycled crustal components has not deviated greatly from the mantle value (~ + 4) and/or Li diffusion is sufficiently fast to attenuate significant heterogeneities over timescales of 10⁸ years. Modeling of Li diffusion at mantle temperatures suggests that limited δ⁷Li variation in the mantle through time reflects the more effective homogenization of Li in the mantle compared to radiogenic isotope systems. The real (but limited) variations in δ⁷Li that exist in modern mantle-derived magmas as well as carbonatites studied here may reflect isotopic fractionation associated with shallow-level processes, such as crustal assimilation and diffusive isotopic fractionation in magmatic systems, with some of the scatter possibly related to low-temperature alteration.     

Cooling-induced fractionation of mantle Li isotopes from the ultraslow-spreading Gakkel Ridge

Li isotopic compositions of magmatic rocks have gained considerable attention recently as probes of mantle-scale processes. However, the concentrations and isotopic composition of Li in mantle minerals from mid-ocean ridges remain relatively unconstrained. This is largely because of the general presence of seawater alteration in abyssal peridotites. Lithium elemental and isotopic compositions for mineral separates of coexisting olivine, clinopyroxene, orthopyroxene and bulk rocks of serpentine-free Gakkel Ridge peridotites were investigated. Bulk rocks have Li contents of 1.6 to 2.7 ppm and δ⁷Li values of 3 to 5‰, which fall within the range of reported normal pristine “MORB mantle” values. Lithium concentrations vary in the order cpx (2.1–4.7 ppm) > opx (0.9–1.7 ppm) ≥ olivine (0.4–0.9 ppm), the opposite found in “equilibrated” mantle peridotite xenoliths (Seitz and Woodland, 2000). The Li isotopic compositions indicate a systematic mineral variation with δ⁷Li_olivine (7.14‰–15.09‰) > δ⁷Li_opx (1.81‰–3.66‰) > δ⁷Li_cpx (?2.43‰ ? ?0.39‰). The δ⁷Li values of cpx are negatively correlated with their Li concentrations with the lightest value for the most enriched cpx grains. There is a first order negative linear correlation between Δ_{olivine–cpx} (δ⁷Li_olivine ? δ⁷Li_cpx) and ^ol/cpxD (Li_olivine/Li_cpx).Numerical simulations indicate that the observed systematic inter-mineral variations of Li concentrations and isotopic compositions could be explained by a cooling driven diffusive redistribution between minerals in a closed system if there is a temperature dependent partitioning of Li between olivine and clinopyroxene. The studied Gakkel Ridge abyssal peridotites may alternatively have cooled under a variable cooling rate with a rapid cooling before the Li system was closed, which is less likely given the tectonic setting. Our calculations confirm that Li systematics in minerals, especially in coexisting mineral phases could potentially be used as a mantle geospeedometer, even for slowly cooled mantle rocks.     

Sources and distribution of organic matter in northern Patagonia fjords,Chile (∼44–47°S): A multi-tracer approach for carbon cycling assessment

We investigated the provenance of organic matter in the inner fjord area of northern Patagonia, Chile (～44–47°S), by studying the elemental (organic carbon, total nitrogen), isotopic (δ¹³C, δ¹⁵N), and biomarker (n-alkanoic acids from vascular plant waxes) composition of surface sediments as well as local marine and terrestrial organic matter. Average end-member values of N/C, δ¹³C, and δ¹⁵N from organic matter were 0.127±0.010, ?19.8±0.3‰, and 9.9±0.5‰ for autochthonous (marine) sources and 0.040±0.018, ?29.3±2.1‰, and 0.2±3.0‰ for allochthonous (terrestrial) sources. Using a mixing equation based on these two end-members, we calculated the relative contribution of marine and terrestrial organic carbon from the open ocean to the heads of fjords close to river outlets. The input of marine-derived organic carbon varied widely and accounted for 13–96% (average 61%) of the organic carbon pool of surface sediments. Integrated regional calculations for the inner fjord system of northern Patagonia covered in this study, which encompasses an area of ～4280 km², suggest that carbon accumulation may account for between 2.3 and 7.8×10⁴ ton C yr^?1. This represents a storage capacity of marine-derived carbon between 1.8 and 6.2×10⁴ ton yr^?1, which corresponds to an assimilation rate of CO₂ by marine photosynthesis between 0.06 and 0.23×10⁶ ton yr^?1. This rate suggests that the entire fjord system of Patagonia, which covers an area of ～240,000 km², may represent a potentially important region for the global burial of marine organic matter and the sequestration of atmospheric CO₂.     

Stratification and mixing of a post-glacial Neoproterozoic ocean: Evidence from carbon and sulfur isotopes in a cap dolostone from northwest China

To improve our knowledge about the geochemical and environmental aftermath of Neoproterozoic global glaciations, we analyzed stable isotopes (δ¹³C, δ¹⁸O, δ³⁴S) and elemental concentrations (Ca, Mg, S, Sr, Fe, and Mn) of the ～ 10-m-thick Zhamoketi cap dolostone atop the Tereeken diamictite in the Quruqtagh area, eastern Chinese Tianshan. Available chemostratigraphic data suggest that the Tereeken diamictite is probably equivalent to the Marinoan glaciation. Our new data indicate that organic and carbonate carbon isotopes of the Zhamoketi cap dolostone show little stratigraphic variations, averaging ? 28.2‰ and ? 4.6‰, respectively. In contrast, sulfur isotopes show significant stratigraphic variations. Carbonate associated sulfate (CAS) abundance decreases rapidly in the basal cap dolostone and δ³⁴S_CAS composition varies between + 9‰ and + 15‰ in the lower 2.5 m. In the overlying interval, CAS abundance remains low while δ³⁴S_CAS rises ～ 5‰ and varies more widely between + 10‰ and + 21‰. The range of δ³⁴S_py of the cap dolostone overlaps with that of δ³⁴S_CAS, but direct comparison shows that δ³⁴S_py is typically greater than δ³⁴S_CAS measured from the same samples. Hypotheses to explain the observations must account for both the remarkable sulfur isotope enrichment of pyrites and the inverse fractionation. We propose that CAS and pyrite were derived from two isotopically distinct reservoirs in a chemically stratified basin or a basin with a sulfate minimum zone. In this model, CAS was derived from shallow, oxic surface waters with moderate sulfate concentration and depleted in ³⁴S due to the post-glacial influx of sulfur from continental weathering. In contrast, pyrite was derived from anoxic bottom waters (or a sulfate minimum zone) with low sulfate concentration and ³⁴S enrichment due to long-term syn-glacial sulfate reduction. The rapid shift in CAS abundance and sulfur isotope composition within the cap dolostone is interpreted to reflect the mixing of the two reservoirs after initial deglaciation. Comparison with other post-Marinoan cap carbonates shows significant spatial heterogeneity in δ³⁴S_CAS, which together with strong temporal variation in δ³⁴S_CAS, points to generally low sulfate concentrations in post-Marinoan oceans.     

Stable isotopic characteristic of Taiwan's precipitation: A case study of western Pacific monsoon region

The stable oxygen and hydrogen isotopic features of precipitation in Taiwan, an island located at the western Pacific monsoon area, are presented from nearly 3,500 samples collected during the past decade for 20 stations. Results demonstrate that moisture sources from diverse air masses with different isotopic signals are the main parameter in controlling the precipitation's isotope characteristics. The air mass from polar continental (Pc) region contributes the precipitation with high deuterium excess values (up to 23‰) and relatively enriched isotope compositions (e.g., ? 3.2‰ for δ¹⁸O) during the winter with prevailing northeasterly monsoon. By contrast, air masses from equatorial maritime (Em) and tropical maritime (Tm) supply the precipitation with low deuterium excess values (as low as about 7‰) and more depleted isotope values (e.g., ? 8.9‰ and ? 6.0‰ for δ¹⁸O of Tm and Em, respectively) during the summer with prevailing southwesterly monsoon. Thus seasonal differences in terms of δ¹⁸O, δD, and deuterium excess values are primarily influenced by the interactions among various precipitation sources. While these various air masses travel through Taiwan, secondary evaporation effects further modify the isotope characteristics of the inland precipitation, such as raindrop evaporation (reduces the deuterium excess of winter precipitation) and moisture recycling (increases the deuterium excess of summer precipitation). The semi-quantitative estimations in terms of evaluation for changes in the deuterium excess suggest that the raindrop evaporation fractions for winter precipitation range 7% to 15% and the proportions of recycling moisture in summer precipitation are less than 5%. Additionally, the isotopic altitude gradient in terms of δ¹⁸O for summer precipitation is ? 0.22‰/100 m, greater than ? 0.17‰/100 m of winter precipitation. The greater isotopic gradient in summer can be attributed to a higher temperature vs. altitude gradient relative to winter. The observed spatial and seasonal stable isotopic characteristics in Taiwan's precipitation not only contribute valuable information for regional monsoon research crossing the continent–ocean interface of East Asia, but also can serve as very useful database for local water resources management.     

Spatial–temporal changes in Andean plateau climate and elevation from stable isotopes of mammal teeth

Paleoelevation constraints from fossil leaf physiognomy and stable isotopes of sedimentary carbonate suggest that significant surface uplift of the northern Andean plateau, on the order of 2.5 ± 1 km, occurred between ～ 10.3 and 6.4 Ma. Independent spatial and temporal constraints on paleoelevation and paleoclimate of both the northern and southern plateau are important for understanding the distribution of rapid surface uplift and its relation to climate evolution across the plateau. This study focuses on teeth from modern and extinct mammal taxa (including notoungulates, pyrotheres, and litopterns) spanning ～ 29 Ma to present, collected from the Altiplano and Eastern Cordillera of Bolivia (16.2°S to 21.4°S), and lowland Brazil. Tooth enamel of large, water-dependent mammals preserves a record of surface water isotopes and the type of plants that animals ingested while their teeth were mineralizing. Previous studies have shown that the δ¹⁸O of modern precipitation and surface waters decrease systematically with increasing elevations across the central Andes. Our results from high elevation sites between 3600 and 4100 m show substantially more positive δ¹⁸O values for late Oligocene tooth samples compared to < 10 Ma tooth δ¹⁸O values. Late Oligocene teeth collected from low elevation sites in southeast Brazil show δ¹⁸O values similar (within 2‰) to contemporaneous teeth collected at high elevation in the Eastern Cordillera. This affirms that the Andean plateau was at a very low elevation during the late Oligocene. Late Oligocene teeth from the northern Eastern Cordillera also yield consistent δ¹³C values of about ? 9‰, indicating that the environment was semi-arid at that time. Latitudinal gradients in δ¹⁸O values of late Miocene to Pliocene fossil teeth are similar to modern values for large mammals, suggesting that by ～ 8 Ma in the northern Altiplano and by ～ 3.6 Ma in the southern Altiplano, both regions had reached high elevation and established a latitudinal rainfall gradient similar to modern.     

Evolution of the oceanic calcium cycle during the late Mesozoic: Evidence from δ44/40Ca of marine skeletal carbonates

The Ca isotope compositions of 37 late Mesozoic skeletal carbonates, belemnites and brachiopods, from the Tethyan realm were analyzed by thermal (TIMS) and plasma (MC-ICP-MS) ionization mass spectrometry. A poor correlation between δ^44/40Ca and δ¹⁸O values of belemnites suggests only a weak temperature dependency for the Ca isotope composition of belemnites, likely less than 0.02‰/°C. The δ^44/40Ca record of belemnites was therefore used to reconstruct the Ca isotope composition of paleo-seawater (δ^44/40Ca_SW), based on an experimentally determined fractionation factor between seawater Ca and belemnite calcite (α_CC–SW) of ∼ 0.9986. The inferred δ^44/40Ca_SW record, with an average stratigraphic resolution of 1 Ma, shows systematic temporal variation of ∼ 0.5‰ with the Middle/Late Jurassic (∼ 154 Ma) minimum of ∼ 1.4‰ and a subsequent general increase to the Early Cretaceous (∼ 124 Ma) maximum of ∼ 1.9‰. The global nature of the δ^44/40Ca_SW record is supported by identical Ca isotope compositions of coeval (Kimmeridgian) belemnites collected from two distinct paleogeographic regions, the southern (New Zealand) and northern (Germany) margin of the Tethys Ocean. The observed late Mesozoic δ^44/40Ca_SW record was simulated using a simple Ca isotope mass balance model, and the results indicate that the variation in δ^44/40Ca_SW record can be explained by changes in oceanic input fluxes of Ca that were independent of the carbonate ion fluxes, such as the hydrothermal Ca flux or the release of Ca to the oceans via dolomitization of marine carbonates.     

Molybdenum isotope signatures in continental margin marine sediments

We present molybdenum isotope data for four sediment profiles from continental margin settings. Each profile has a distinctive average isotope composition ranging from δ^98 / 95Mo − 0.5‰ to 1.3‰ (relative to J and M laboratory standard). This range lies between the modern ocean water value (2.3‰) and the values typical of Mo adsorbed onto Mn oxides (− 0.7‰ ± 0.1‰). An important finding of this study is the apparent co-variation between the Mo isotope composition and the accumulation rate of authigenic Mo under reducing conditions. This relationship suggests that the chemical processes responsible for Mo accumulation under reducing conditions produce an isotope signature in marine sediments. In addition to the relationship between Mo accumulation and the Mo isotope signature there is also a relationship between these parameters and the rate of organic carbon oxidation and burial. These relationships suggest that the Mo isotope signature of reducing sediments may serve as a tracer for the cycling of organic carbon in continental margin sediments; however, additional data will be required to refine any such relationships.     

Himalayan metamorphic CO2 fluxes: Quantitative constraints from hydrothermal springs

Hot springs in the Marsyandi Valley, Nepal, vent CO₂ sourced from metamorphic fluids that mix with shallow groundwaters before degassing near the Earth's surface. The δ¹³C of spring waters ranges up to + 13‰, while that of the coexisting free gas phase is close to ? 4‰. Empirical and thermodynamic modelling of this isotopic fractionation suggests > 97 ± 1% CO₂ degassing. The calculated minimum total CO₂ degassing in the Marsyandi catchment is 5.4 × 10⁹ mol/yr from a Cl-based estimate of the spring water discharge to the Marsyandi River and the fraction of CO₂ degassed. Extrapolated to the whole of the Himalayas, this implies a probable minimum metamorphic CO₂ flux of 0.9 × 10¹² mol/yr, or ～ 13% of solid Earth CO₂ degassing. The calculated flux is a factor of three greater than the estimated CO₂ drawdown by silicate weathering in the Himalayas. Himalayan metamorphic degassing contributes a significant fraction of the global solid Earth CO₂ flux and implies that metamorphism may cause changes in long-term climate that oppose those resulting from the orogenic forcing of chemical weatherability.     

40Ar/39Ar geochronology using a quadrupole mass spectrometer

Magnetic sector mass spectrometers dominate the field of ⁴⁰Ar/³⁹Ar geochronology. Recent advances in quadrupole mass spectrometer technology, especially improvements in resolution, have increased the performance of these instruments to the extent that they can be used for isotopic determinations. We describe a triple filter quadrupole mass spectrometer (Hiden HAL 3F Series Pulse Ion Counting Triple Filter QMS) linked to an automated furnace extraction and cleaning system dedicated to ⁴⁰Ar/³⁹Ar incremental heating experiments.The instrument produces peaks with broad flat tops and a width of 0.9 amu at 10 cps height and 0.84 amu at 500,000 cps height on a 1 million cps high peak (peak width at 0.01‰ and 50% peak height respectively). This allows measurement of ratios of the main Ar peaks in the 1‰ range. Measurements of 1.6 × 10^?12 mole of air reference gas over two years yields ⁴⁰Ar/³⁶Ar = 257.9 ± 1.3 (1σ, n = 34). The ability of the instrument to produce ⁴⁰Ar/³⁹Ar ages from rocks/minerals of a wide age range, reaching into the late Quaternary, are demonstrated by a series of tests and comparison with geochronological data from other studies and an in-house MAP 215-50 magnetic sector mass spectrometer. We demonstrate that high-end quadrupole systems can be used for routine ⁴⁰Ar/³⁹Ar dating purposes.     

Mercury emissions and stable isotopic compositions at Vulcano Island (Italy)

Sampling and analyses methods for determining the stable isotopic compositions of Hg in an active volcanic system were tested and optimized at the volcanic complex of Vulcano (Aeolian Islands, Italy). Condensed gaseous fumarole Hg_(fum)^T, plume gaseous elemental Hg_(g)⁰ and plume particulate Hg_(p)^II were obtained at fumaroles F0, F5, F11, and FA. The average total Hg emissions, based on Hg^T/SO₂ in condensed fumarolic gases and plumes, range from 2.5 to 10.1 kg y^? 1, in agreement with published values [Ferrara, R., Mazzolai, B., Lanzillotta, E., Nucaro, E., Pirrone, N., 2000. Volcanoes as emission sources of atmospheric mercury in the Mediterranean Basin. Sci. Total Environ. 259(1–3), 115–121; Aiuppa, A., Bagnato, E., Witt, M.L.I., Mather, T.A., Parello, F., Pyle, D.M., Martin, R.S., 2007. Real-time simultaneous detection of volcanic Hg and SO₂ at La Fossa Crater, Vulcano (Aeolian Islands, Sicily). Geophys. Res. Lett. 34(L21307).]. Plume Hg_(p)^II increases with distance from the fumarole vent, at the expense of Hg_(g)⁰ and indicates significant in-plume oxidation and condensation of fumarole Hg_(fum)^T.Relative to the NIST SRM 3133 Hg standard, the stable isotopic compositions of Hg are δ²⁰²Hg_(fum)^T = ? 0.74‰ ± 0.18 (2SD, n = 4) for condensed gaseous fumarole Hg_(fum)^T, δ²⁰²Hg_(g)⁰ = ? 1.74‰ ± 0.36 (2SD, n = 1) for plume gaseous elemental Hg_(g)⁰ at the F0 fumarole, and δ²⁰²Hg_(p)^II = ? 0.11‰ ± 0.18 (2SD, n = 4) for plume particulate Hg_(p)^II. The enrichment of Hg_(p)^II in the heavy isotopes and Hg_(g)⁰ in the light isotopes relative to the total condensed fumarolic Hg_(fum)^T gas complements the speciation data and demonstrates a gas-particle fractionation occurring after the gas expulsion in ambient T° atmosphere. A first order Rayleigh equilibrium condensation isotope fractionation model yields a fractionation factor α_cond-gas of 1.00135 ± 0.00058.     

Subduction erosion of forearc mantle wedge implicated in the genesis of the South Sandwich Island (SSI) arc: Evidence from boron isotope systematics

The South Sandwich volcanic arc is sited on a young oceanic crust, erupts low-K tholeiitic rocks, is characterized by unexotic pelagic and volcanogenic sediments on the down-going slab, and simple tectonic setting, and is ideal for assessing element transport through subduction zones. As a means of quantifying processes attending transfer of subduction-related fluids from the slab to the mantle wedge, boron concentrations and isotopic compositions were determined for representative lavas from along the arc. The samples show variable fluid-mobile/fluid-immobile element ratios and high enrichments of B/Nb (2.7 to 55) and B/Zr (0.12 to 0.57), similar to those observed in western Pacific arcs. δ¹¹B values are among the highest so far reported for mantle-derived lavas; these are highest in the central part of the arc (+ 15 to + 18‰) and decrease toward the southern and northern ends (+ 12 to + 14‰). δ¹¹B is roughly positively correlated with B concentrations and with ⁸⁷Sr/⁸⁶Sr ratios, but poorly coupled with other fluid-mobile elements such as Rb, Ba, Sr and U. Peridotites dredged from the forearc trench also have high δ¹¹B (ca. + 10‰) and elevated B contents (38–140 ppm). Incoming pelagic sediments sampled at ODP Site 701 display a wide range in δ¹¹B (+ 5 to ? 13‰; average = ? 4.1‰), with negative values most common. The unusually high δ¹¹B values inferred for the South Sandwich mantle wedge cannot easily be attributed to direct incorporation of subducting slab materials or fluids derived directly therefrom. Rather, the heavy B isotopic signature of the magma sources is more plausibly explained by ingress of fluids derived from subduction erosion of altered frontal arc mantle wedge materials similar to those in the Marianas forearc. We propose that multi-stage recycling of high-δ¹¹B and high-B serpentinite (possibly embellished by arc crust and volcaniclastic sediments) can produce extremely ¹¹B-rich fluids at slab depths beneath the volcanic arc. Infiltration of such fluids into the mantle wedge likely accounts for the unusual magma sources inferred for this arc.     

Persistent organic pollutants and stable isotopes in pinnipeds from King George Island,Antarctica

In the present work, fat, skin, liver and muscle samples from Leptonychotes weddellii (Weddell seal, n = 2 individuals), Lobodon carcinophagus (crabeater seal, n = 2), Arctocephalus gazella (Antarctic fur seal, n = 3) and Mirounga leonina (southern elephant seal, n = 1) were collected from King George Island, Antarctica, and analysed for POPs (PCBs, organochlorine pesticides and PBDEs) and stable isotopes (δ¹³C and δ¹⁵N in all tissues but fat). PBDEs could be found in only one sample (L. weddellii fat). Generally, PCBs (from 74 to 523 ng g⁻¹ lw), DDTs (from 14 to 168 ng g⁻¹ lw) and chlordanes (from 9 to 78 ng g⁻¹ lw) were the prevailing compounds. Results showed a clear stratification in accordance with ecological data. Nonetheless, stable isotope analyses provide a deeper insight into fluctuations due to migrations and nutritional stress. Correlation between δ¹⁵N and pollutants suggests, to some degree, a considerable ability to metabolize and/or excrete the majority of them.     

High-precision 40Ar/39Ar age of the Jänisjärvi impact structure (Russia)

The ～ 14 km diameter Jänisjärvi impact structure is located in Svecofennian Proterozoic terrain in the southeastern part of the Baltic shield, Karelia, Russia. Previous radioisotopic dating attempts gave K/Ar and ⁴⁰Ar/³⁹Ar ages of 700 ± 5 Ma and 698 ± 22 Ma, respectively, with both results being difficult to interpret. Recent paleomagnetic results have challenged these ages and proposed instead ages of either 500 Ma or 850–900 Ma. In order to better constrain the age of the Jänisjärvi impact structure, we present new ⁴⁰Ar/³⁹Ar data for the Jänisjärvi impact melt rock. We obtained five concordant isochron ages that yield a combined isochron age of 682 ± 4 Ma (2σ) with a MSWD of 1.2, P = 0.14, and ⁴⁰Ar/³⁶Ar intercept of 475 ± 3. We suggest that this date indicates the age of the impact and therefore can be used in conjunction with existing paleomagnetic results to define the position of the Baltica paleocontinent at that time. Argon isotopic results imply that melt homogenization was achieved at the hundred-micrometer scale certainly, because of the low-silica content of the molten target rock that allows fast ⁴⁰Ar^? diffusion in the melt. However, the large range of F(⁴⁰Ar^?_inherited) (4.1% to 11.0%) observed for seven grains shows that complete isotopic homogenization was not reached at the centimeter and perhaps the millimeter scale. The F(⁴⁰Ar^?_inherited) results are also in good agreement with previous Rb and Sr isotopic data.     

On the comparison of tidal gravity parameters with tidal models in central Europe

Two accurately calibrated superconducting gravimeters (SGs) provide high quality tidal gravity records in three central European stations: C025 in Vienna and at Conrad observatory (A) and OSG050 in Pecný (CZ). To correct the tidal gravity factors from ocean loading effects we compared the load vectors from different ocean tides models (OTMs) computed with different software: OLFG/OLMP by the Free Ocean Tides Loading Provider (FLP), ICET and NLOADF. Even with the recent OTMs the mass conservation is critical but the methods used to correct the mass imbalance agree within 0.1 nm/s². Although the different software agrees, FLP probably provides more accurate computations as this software has been optimised. For our final computation we used the mean load vector computed by FLP for 8 OTMs (CSR4, NAO99, GOT00, TPX07, FES04, DTU10, EOT11a and HAMTIDE). The corrected tidal factors of the 3 stations agree better than 0.04% in amplitude and 0.02° in phase. Considering the weighted mean of the three stations we get for O1 δ_c = 1.1535 ± 0.0001, for K1 δ_c = 1.1352 ± 0.0003 and for M2 δ_c = 1.1621 ± 0.0003. These values confirm previous ones obtained with 16 European stations. The theoretical body tides model DDW99/NH provides the best agreement for M2 (1.1620) and MATH01/NH for O1 (1.1540) and K1 (1.1350). The largest discrepancy is for O1 (0.05%). The corrected phase α_c does not differ significantly from zero except for K1 and S2. The calibrations of the two SG's are consistent within 0.025% and agree with Strasbourg results within 0.05%.     

Permo-Pennsylvanian palaeotemperatures from Fe-Oxide and phyllosilicate δ18O values

The oxygen isotope composition of fossil roots that have been permineralized by hematite are presented from eight different stratigraphic levels spanning the Upper Pennsylvanian and Lower Permian strata of north-central Texas. Hematite δ¹⁸O values range from − 0.4% to 3.7%. The most negative δ¹⁸O values occur in the upper Pennsylvanian strata, and there is a progressive trend toward more positive δ¹⁸O values upward through the lower Permian strata. This stratigraphic pattern is similar in magnitude and style to δ¹⁸O values reported for penecontemporaneous authigenic palaeosol phyllosilicates and calcites, suggesting that all three minerals record similar paragenetic histories that are probably attributed to temporal palaeoenvironmental changes across the Late Pennsylvanian and Early Permian landscapes.Palaeotemperature estimates based on paired δ¹⁸O values between penecontemporaneous hematite and phyllosilicate samples suggest these minerals co-precipitated at relatively low temperatures that are consistent with a supergene origin in a low-latitude soil-forming environment. Hematite–phyllosilicate δ¹⁸O pairs indicate (1) relatively low soil temperatures (∼ 24 ± 3 °C) during deposition of the upper Pennsylvanian strata followed by (2) a considerable rise in soil temperatures (∼ 35–37 ± 3 °C) during deposition of the lowermost Permian strata. Significantly, δD and δ¹⁸O values of contemporaneous phyllosilicates provide single mineral palaeotemperature estimates that are analytically indistinguishable from temperature estimates based on hematite–phyllosilicate oxygen isotope pairs. The results between the two temperature-proxy methods suggest that the inferred large temperature change across the Upper Pennsylvanian–Lower Permian boundary might be taken seriously. If real, such a significant climate change would have undoubtedly had far-reaching ecological effects within this region of Pangaea. Notably, there are important lithological and palaeobotanical changes, such as disappearance of coal and coal swamp floras, across the Upper Pennsylvanian–Early Permian boundary of north-central Texas that may be consistent with major climatic change toward warmer conditions.