Nickel Isotope Variations in Terrestrial Silicate Rocks and Geological Reference Materials Measured by MC-ICP-MS

International audienceAlthough initial studies have demonstrated the applicability of Ni isotopes for cosmochemistry and as a potential biosignature, the Ni isotope composition of terrestrial igneous and sedimentary rocks, and ore deposits remains poorly known. Our contribution is fourfold: (a) to detail an analytical procedure for Ni isotope determination, (b) to determine the Ni isotope composition of various geological reference materials, (c) to assess the isotope composition of the Bulk Silicate Earth relative to the Ni isotope reference material NIST SRM 986 and (d) to report the range of mass-dependent Ni isotope fractionations in magmatic rocks and ore deposits. After purification through a two-stage chromatography procedure, Ni isotope ratios were measured by MC-ICP-MS and were corrected for instrumental mass bias using a double-spike correction method. Measurement precision (two standard error of the mean) was between 0.02 and 0.04‰, and intermediate measurement precision for NIST SRM 986 was 0.05‰ (2s). Igneous- and mantle-derived rocks displayed a restricted range of δ60/58Ni values between −0.13 and +0.16‰, suggesting an average BSE composition of +0.05‰. Manganese nodules (Nod A1; P1), shale (SDO-1), coal (CLB-1) and a metal-contaminated soil (NIST SRM 2711) showed positive values ranging between +0.14 and +1.06‰, whereas komatiite-hosted Ni-rich sulfides varied from −0.10 to −1.03‰

ICES Viewpoint background document: Impact from exhaust gas cleaning systems (scrubbers) on the marine environment (Ad hoc).

Shipping is a diverse industry that connects the world. The distribution and intensity of commercial shipping is increasing and there is a growing need to assess and mitigate the impacts of vessel activities on the marine environment. New global standards on sulphur content in marine fuels have led to an increasing number of ships installing exhaust gas cleaning systems (EGCS), also known as scrubbers, to reduce their emissions of sulphur oxides to the atmosphere. Ships equipped with a scrubber can continue to use heavy fuel oil, and the process results in discharges of large volumes of acidified water that contain a mix of contaminants, such as heavy metals, polycyclic aromatic hydrocarbons (PAHs), oil residues, and nitrates. For the most common type of scrubber, open loop, this polluted water is directly discharged back to the sea, trading reductions in air pollution for increased water pollution. The scrubber discharge mixture has demonstrated toxic effects in laboratory studies, causing immediate mortality in plankton and exhibiting negative synergistic effects. The substances found in scrubber discharge water are likely to have further impacts in the marine environment through bioaccumulation, acidification and eutrophication. The impacts of scrubber discharge water can be completely avoided through the use of alternative fuels, such as distilled low sulphur fuels. Distilled fuels have the added benefit that they remove the threat of heavy fuel oil spills from shipping activities. If the use of alternative fuels is not adopted, and scrubbers continue to be considered an equivalent method to meet the sulphur emissions limits, then there is urgent need for:1) significant investment in technological advances and port reception facilities to allow zero discharge closed loop scrubber systems;2) improved protocols and standards for measuring, monitoring and reporting on scrubber discharge water acidity and pollutants;3) evidence-based regulations on scrubber water discharge limits that consider the full suite of contaminants

Multidisciplinary investigation on cold seeps with vigorous gas emissions in the Sea of Marmara (MarsiteCruise): Strategy for site detection and sampling and first scientific outcome

MarsiteCruise was undertaken in October/November 2014 in the Sea of Marmara to gain detailed insight into the fate of fluids migrating within the sedimentary column and partially released into the water column. The overall objective of the project was to achieve a more global understanding of cold-seep dynamics in the context of a major active strike-slip fault. Five remotely operated vehicle (ROV) dives were performed at selected areas along the North Anatolian Fault and inherited faults. To efficiently detect, select and sample the gas seeps, we applied an original procedure. It combines sequentially (1) the acquisition of ship-borne multibeam acoustic data from the water column prior to each dive to detect gas emission sites and to design the tracks of the ROV dives, (2) in situ and real-time Raman spectroscopy analysis of the gas stream, and (3) onboard determination of molecular and isotopic compositions of the collected gas bubbles. The in situ Raman spectroscopy was used as a decision-making tool to evaluate the need for continuing with the sampling of gases from the discovered seep, or to move to another one. Push cores were gathered to study buried carbonates and pore waters at the surficial sediment, while CTD-Rosette allowed collecting samples to measure dissolved-methane concentration within the water column followed by a comparison with measurements from samples collected with the submersible Nautile during the Marnaut cruise in 2007. Overall, the visited sites were characterized by a wide diversity of seeps. CO2- and oil-rich seeps were found at the westernmost part of the sea in the Tekirdag Basin, while amphipods, anemones and coral populated the sites visited at the easternmost part in the Cinarcik Basin. Methane-derived authigenic carbonates and bacterial mats were widespread on the seafloor at all sites with variable size and distributions. The measured methane concentrations in the water column were up to 377 μmol, and the dissolved pore-water profiles indicated the occurrence of sulfate depleting processes accompanied with carbonate precipitation. The pore-water profiles display evidence of biogeochemical transformations leading to the fast depletion of seawater sulfate within the first 25-cm depth of the sediment. These results show that the North Anatolian Fault and inherited faults are important migration paths for fluids for which a significant part is discharged into the water column, contributing to the increase of methane concentration at the bottom seawater and favoring the development of specific ecosystems

A Metrological Approach to Analytical Biases for MC-ICP-MS Isotope Ratio Measurements - Application to the Certification of New Pb Isotopic Reference Materials (Candidate ERM-38xx Series)

Lead (PB) is known to be a particularly toxic chemical element since several centuries. Mining and smelting of Pb and its domestic use have contaminated the surface of Earth and jeopardized the health of humans, domestic animals and wildlife. Consequently, regulations were progressively introduced to control, restrict or ban the use and dissemination of lead compounds. Currently, Pb is one of the few metals covered by the legislation (European directives EC-82/884/EEC, 1999/30/EC and 200/60/EC). Omnipresence of PB has however and advantage. It can be used as an isotopic tracer of pollution sources and pathways in the environment. Pb isotopic Certified Reference Materials (iCRM) with undisputed characteristics are then required to validate Pb isotope ratio measurements. The materials currently available worldwide were produced in the 1960¿s by the National Bureau of Standards in the USA and are now the object of polemics in the scientific literature regarding the accuracy of some of the accompanying certified values. Moreover, new materials with lower relative uncertainty statements (below 0.01%) are demanded by users. This PhD work was centred on the production and the certification of a new series of Pb iCRM (candidate ERM-38xx series). The production included sic Pb gravimetric isotope mixtures, a common Pb material dedicated to routine calibration work and a series of four 207Pb slightly enriched natural-like Pb materials for the validation of the ¿-scale method below 0.1%o. The gravimetric isotope mixtures method, originally supported by mass spectrometry measurements performed on GS-MS or TI-MS instruments, was applied successfully to MC-ICP-MS. This study demonstrated that this isotopic measurement technique is a portential powerful tool for the certification of new iCRM. It necessitated in certain cases methodological adjustments which are discussed hereafter. MC-ICp-MS instrumental biases and especially mass discrimination effects, which are still not well understood, were investigated to guaranty the reliability of the produced iCRM. Our measurements methods were validate by several ways, including a systematic investigation on possible significant sources of uncertainty, several comparisons of results obtained by different methods and different laboratories and of course an extensive use of reference materials. Relative uncertainties on isotope ratios obtained for the newly produced Pb iCRM are as low as 0.017%, which is between 2 and 4 times smaller than the uncertainties carried by the NIST-981 material. Additionally, we propose new reference values for this material that was measured agains our independent Pb iCRM. It was not possible to produce iCRM carrying reference values with relative uncertainties below 0.01% as demanded by the Pb community, mainly because of uncompressible uncertainties coming from the weighing stage. We suggest that the newly produced 207Pb series, for which the ¿-values span from 0.001%to 0.013%, could be used as validation tool for isotopic variations below 0.01% (sub-epsilon scale measurements). Results obtained from an inter-laboratory comparison (involving 5 laboratories) on ¿-scale measurements show that relative isotopic variations below 0.005% are hardly measurable accurately.JRC.D.4-Isotope measurement

In situ Lithium and Boron isotope determinations in mica, pyroxene, and serpentine by LA-MC-ICP-MS

Boron and Li are light, incompatible elements that preferentially partition into the liquid phase, whether melt or aqueous fluid, and thus are useful for tracking fluid-related processes in rocks. Most of the Li isotopic data presently available on subduction-related rocks are from whole-rock analyses; and the B isotopic analyses of subduction material have been carried out either on whole-rocks or in-situ on an accessory phase, such as tourmaline. The new method presented here couples an ESI New Wave UP-193-FX ArF* (193 nm) excimer laser-ablation microscope with a Neptune Plus (Thermo Scientific) MC-ICP-MS aiming to measure both Li and B isotopes in situ with good spatial resolution (metamorphic minerals are commonly chemically zoned, and whole-rock analyses lose this detail). The data thus obtained are compared with SIMS analyses on the same mineral samples for B, and with MC-ICP-MS analyses on whole-rock or mineral separates from the same sample for Li. Additionally, data acquired on tourmaline standards were compared to SIMS values. The results show that for B concentrations above 5 μg/g, the data obtained by LA-MC-ICP-MS and by SIMS are identical within error, for mica (phengitic muscovite), pyroxene (jadeite), serpentine (antigorite), and tourmaline. For Li concentrations above 10 μg/g, the data obtained by LA-MC-ICP-MS and by MC-ICP-MS are also identical, within error, for mica (phengitic muscovite), and pyroxene (jadeite). However, analyses of tourmaline standards have shown significant differences with reference values, so LA-MC-ICP-MS does not yet appear to be an appropriate method to analyze Li isotopes in tourmalines. Thus, LA-MC-ICP-MS is a suitable method to measure Li and B isotopes with good spatial resolution in major rock-forming silicates from subduction-related rocks where concentrations exceed 10 μg/g and 5 μg/g, respectively, with an error on individual measurements equal to or less than previously used methods, but obtainable in a significantly shorter amount of time. The external reproducibility is ± 2.88 to 3.31 ‰ for B and ± 1.50 to 1.75 for Li, which is lower than or equal to the variations encountered within a given chemically zoned sample (up to 10 ‰ of variation within a given natural sample)

Trace metals and PAHs discharge from ships with Exhaust Gas Cleaning System (EGCS)

With the new global sulphur shipping emission regulations of International Maritime Organization (IMO), remarkable increase of exhaust gas cleaning systems (EGCS) installations was noted recently. EGCS, also known as “scrubbers”, is an alternative technical solution reducing air emission of sulphur oxides, appeared as an attractive, less-expensive solution for many ship companies. EGCS allows ships to continue to use low-cost, high-sulfur heavy fuel oil (HFO) and consequently the shipping industry remains main market for HFO. In the scrubber, the ship exhaust gas is washed out by a high flow rate of the seawater and this process results in the effective reduction of sulphur air emission and in the discharge overboard into surrounding environments of a large amount of polluted washwaters. The resulting discharged washwaters contain a chemical mixture of acidifying and eutrophying substances and toxic pollutants such as heavy metals and polycyclic aromatic hydrocarbons (PAHs), which together with SOx are effectively washed out from the ship exhausts. The use of scrubbers generates thus a new stream of shipping liquid wastes, which will dominate metals and PAH discharges from ships.  In this context, there is a growing need to elaborate and improve the methods for evaluation of pollutant discharge through scrubbers and the routine monitoring of this chemical pollution transferred from air to marine waters. In the present report the focus is given primarily on emission discharges of heavy metals and PAHs that is two groups of ship exhaust contaminants, which were less studied and regulated. In essence, the proposed method for scrubber emission discharge evaluation, is built on the same basis as approved methods developed for green-house gases (GHGs) and main shipping air pollutant emission inventories. In this respect, the proposed approach is based on the estimates using pollutant emission factors, washwater volumes and flow rates, assumed scrubber trapping efficiencies, ship fuel consumption and energy demand. The case study of the metals and PAHs discharge estimation is proposed for the model Ro-Pax ferry - one ship scenario and its real-world operation between two ports Marseille and Ajaccio (France). A larger scale projection is also presented, consisting of the potential pollutant discharges by EGCS of 11 Ro-Pax ships fleet also operating in the Gulf of Lion and the Ligurian Sea basins, between mainland France and Corsica. Furthermore, building on the recent work by Osipova et al. (2021) on the global assessment of the mass of washwater discharges from vessels using scrubbers, our report provides various scenarios of washwater and pollutant loads into French Exclusive Economic Zone (EEZ). The calculations are presented for the entire French EEZ as well as the French Mediterranean EEZ and its ports in the Gulf of Lion (GoL) and Corsica. It appears that in France about 75 % of scrubber washwater discharges occur beyond territorial sea of 12 nautical miles, whereas 15 % is released in the territorial seas (TS), 6 % in internal waters (IW) and 4% in their ports. The distribution of pollutant loads will follow washwater discharges. Pollutant quantities amounting to hundreds and thousands of kilograms of main metals (V, Fe, Ni, Zn) and PAHs discharged annually by a given fleet of 11 Ro-Pax ships into the Western Mediterranean Sea come into the same category as other large-scale environmental inputs and emissions of these compounds. The estimated annual EGCS potential loads to the Gulf of Lion and the Ligurian Sea compare to the amounts of vanadium, nickel and ƩPAH16 dumped with major oil spills or to the Rhone river annual flux of PAHs entering the Gulf of Lion. These estimates clearly indicate that ship scrubber washwaters may represent significant source of pollutants entering the western Mediterranean Sea

Determination of ultra-low U-236/U-238 isotope ratios by tandem quadrupole ICP-MS/MS

Isotope ratios of U-236/U-238 were measured at levels below 10(-7) by single collector ICPMS with a tandem quadrupole mass separation mechanism. Peak tailing of the prominent U-238(+) ion beam on the U-236(+) peak was reduced to the level of similar to 10(-10) by use of two quadrupole mass filters. The (UH+)-U-235 interference on U-236(+) was efficiently reduced to a UH+/U+ ratio of 1 x 10(-8) by an ion-molecule reaction between UH+ and O-2 in a collision/reaction cell placed between the two quadrupoles. The resultant detection limit for U-236/U-238 measurement was better than those reported by any other ICPMS study. The U-236/U-238 ratios, measured as (UO+)-U-236-O-16/(UO+)-U-238-O-16, were determined in the range 10(-9) to 10(-7) without correction for spectral interference. Accurate measurements of U-236/U-238 to as low as 1 x 10(-10) are projected

Paleo-environmental controls on cold seep carbonate authigenesis in the Sea of Marmara

International audienceThe factors controlling fluid emission dynamics at ocean margins are poorly understood. In particular, there are significant uncertainties on how fluid seepage at cold seeps may have responded to abrupt environmental changes in the geological past. This study reports on a detailed geochemical investigation of seafloor carbonate crusts sampled at cold seeps along the submerged part of the North Anatolian Fault system in the Sea of Marmara - an inland sea, which has experienced major paleo-environmental changes over the last deglaciation period. We also analyzed a series of authigenic carbonate concretions recovered from two sediment cores at the Western-High ridge, an active fluid venting area. The ages of seafloor carbonate crusts derived from isochron U-Th dating cover the last 7 kyr, suggesting that fluid activity along the fault system remained continuous over that time interval. In the sediment cores, carbonate concretions are concentrated at the lacustrine-to-marine transition, which corresponds to the period when Mediterranean waters flowed into the Marmara Basin about 12-14 kyr ago. U-Th isotopic data indicate that most of these concretions formed later during the Holocene, around 9-10 kyr ago, a period coinciding with an important anoxic event that led to the deposition of a sapropel layer in the Sea of Marmara. Based upon these results, we suggest that the absence of carbonate concretions in the lacustrine sediment unit indicates that dissolved sulfate concentrations in the Marmara lake pore waters during glacial time were too low to promote significant anaerobic methane oxidation, thereby preventing sedimentary carbonate authigenesis. In contrast, the progressive inflow of Mediterranean waters into the glacial Marmara lake after 15 ka provided a source of dissolved sulfate that allowed anaerobic oxidation of methane to proceed within the anoxic sediment. Importantly, the synchronism between the main phase of authigenic carbonate precipitation at the studied sites (average 9.4±1.8 ka, n=16) and the regional anoxic sapropel event support the idea that the drop in bottom water dissolved oxygen content was probably a key factor to enhance microbial activity and associated carbonate precipitation at that time. Overall, these results provide straightforward evidence that fluid emission dynamics and hydrocarbon oxidation at cold seeps can be directly related to changing environmental conditions through time