Closed System Model Research Articles

Measurement and characteristics of radon flow in an extremely arid region based on a closed-system earth-air model

Radon (222Rn) is a radioactive gas that occurs naturally in the soil and is harmful to the environment and health. However, the measuring the amount of radon flowing is challenging. This study reveals the mechanism responsible for radon transportation and concentration variation, the main driving forces acting, and the key factors operating in the vadose zone. In this study, two separate holes were used to monitor the amount of earth-air and radon flowing in and out of the soil in the extremely arid region in China where the Mogao Grottoes are located. Using a closed-system model, the quantity, characteristics, and regularity of the flow of earth-air and radon were thus determined on daily and yearly timescales. The same patterns of variation in earth-air flow and radon concentration were found at the two sites, both depending on the variation in the atmospheric pressure (AP). When the AP decreases, earth-air flows out from the soil with a high radon concentration. Conversely, when the AP increases, earth-air enters into the soil with a low radon concentration. Thus, radon is continuously emitted from the soil. The concentration of radon in the earth-air is proportional to the rate of flow of earth-air and therefore increases as the AP decreases. The radon emission also varies with the seasonal variation in temperature and AP, which is high in summer and low in winter. On a daily timescale, the radon varies in a bimodal manner. Therefore, the net amount of radon emitted from the soil is positively correlated with the amplitude of the AP fluctuation, temperature, soil porosity, and thickness of the vadose zone. The atmospheric pumping is the main driving force responsible for the radon emission. However, the surface closure, landform, cracks, faults, grain size, pore structure, soil adsorption, basal uranium/radium, salts, wind, lunar cycle, latitude and altitude have important effects on the number of radon emission. As such, it provides a scientific basis for the effective utilization of radon and prevention of its emission from soil.

Postcumulus Processes Recorded in Whole-Rock Geochemistry: a Case Study from the Mirabela Layered Intrusion, Brazil

Abstract According to the ‘trapped liquid’ paradigm, whole-rock chemical compositions of cumulate rocks in layered intrusions can be represented as closed-system multicomponent mixtures of the cumulus phases and the liquids from which they crystallised. Alternative open-system models for cumulate solidification assert that intercumulus liquid is continuously mobile as a result of compaction of crystal mushes. In the closed-system models, all excluded elements, i.e. those incompatible in the cumulus phases, should be correlated with one another, whereas in open systems the more incompatible elements should be decoupled from the more compatible ones and correlations should be poor. These alternative hypotheses are tested using a database of >63 000 whole-rock analyses of mostly ultramafic cumulates from a single package of layers across the entire width of the Mirabela layered intrusion, a 2.5-km-wide by >2-km-thick intrusion with Great Dyke-like stratigraphy. Variably compatible elements Al, Na, Ti and P are found to show strong correlations with one other in olivine-pyroxene cumulates across the spectrum from mesocumulate to orthocumulate rocks, where drill-core sample intervals are composited over 3 m; weaker correlations are found over 1-m sample intervals. The closed-system trapped liquid model is robust for this suite of rocks at the scale of 3-m lengths of drill core (~1 kg of sample). Furthermore, a very smooth and symmetrical variation is observed from dominantly ad- to mesocumulate rocks in the geometrical centre of the intrusion towards orthocumulates at both margins, attributable to increase in cooling rate towards the margins. The most adcumulate rocks are gabbronorites at the base of the mafic sequence in the centre of the intrusion. There is no corresponding decrease in layer thickness towards the centre that would be predicted by a compaction model. The only incompatible element showing partial decoupling is K, which appears to have been mobile at a very late stage, probably in an aqueous fluid phase. There is no evidence for mobilisation of platinum group elements or other chalcophile elements by this fluid despite the presence of disseminated sulfide throughout the sampled interval.

Capture and inactivation of viral particles from bioaerosols by electrostatic precipitation

Infectious viral particles in bioaerosols generated during laparoscopic surgery place staff and patients at significant risk of infection and contributed to the postponement of countless surgical procedures during the COVID-19 pandemic causing excess deaths. The implementation of devices that inactivate viral particles from bioaerosols aid in preventing nosocomial viral spread. We evaluated whether electrostatic precipitation (EP) is effective in capturing and inactivating aerosolized enveloped and non-enveloped viruses. Using a closed-system model mimicking release of bioaerosols during laparoscopic surgery, known concentrations of each virus were aerosolized, exposed to EP and collected for analysis. We demonstrate that both enveloped and non-enveloped viral particles were efficiently captured and inactivated by EP, which was enhanced by increasing the voltage to 10kV or using two discharge electrodes together at 8kV. This study highlights EP as an effective means for capturing and inactivating viral particles in bioaerosols, which may enable continued surgical procedures during future pandemics.

Textural characterization of unidirectional solidification textures related to Cu–Au deposits and their implication for metallogenesis and exploration

Ten rock samples with unidirectional solidification textures (USTs) from nine Asian and Australian porphyry and intrusion-related Au deposits and prospects were investigated in terms of mineralization sequences, textural and paragenetic relationships, melt and fluid inclusion inventory, cathodoluminescence, and trace elements of UST quartz. Despite general similar structural appearance of the investigated UST sequences, each UST locality has its own specific textural features. We provide a structural classification of observed USTs that distinguishes equigranular and heterogranular USTs, which are subdivided according to the UST layer structure into straight, wavy, or contorted/brain-like type. In addition, there is the group of disturbed USTs comprising incompletely developed UST layers, and ductile- or brittle-fragmented UST sequences. Ti-in-quartz-based calculations revealed crystallization temperatures of UST quartz between 590 and 770 °C. Primary silicate melt inclusions found in four samples indicate that quartz crystallized initially from a silicate melt. In five samples, fluid inclusion “boiling” assemblages were observed, documenting brine-vapor phase separation due to pressure drop. In one case, the “boiling” assemblage is in primary inclusions and in the other cases the assemblages have been trapped in pseudosecondary inclusions in a later stage. Primary brine inclusions without coeval vapor-rich inclusions were identified in one sample only. Our results permit UST formation in either an open-system setting where fluids exsolved from UST crystallization are periodically released by fracturing (pressure drops) after the formation of each individual UST layer, or closed-system setting where the exsolved fluids are trapped because of lack of fracturing as long the UST sequence forms. Here, the closed-system model is introduced for the first time to describe the formation of layered quartz UST sequences in porphyry systems where the open-system setting seems to be not applicable. Nonetheless, quartz UST sequences are very important exploration vectors for porphyry systems. Six out of the ten UST samples are high-grade with up to 12 g/t Au. However, in the investigated cases, the Au mineralization postdates UST formation. At Oyut Ulaan and Tampang, the UST quartz formation is co-genetic with major Cu–Fe sulfide mineralization, whereas in the other localities the UST formation predates the sulfide mineralization. In any case, UST layer sequences clearly functioned as an outer carapace and, thus, as a chemo-physical trap of passing mineralizing fluids entering the UST structure and may offer a vector to the main stockwork mineralization, which might occur 100 to 200 m above the UST zone.

82. Enabling large scale precision oncology research with a new standard for genomic variants: OMOP Genomic

Precision Oncology requires the application of genomic variants to epidemiological methods used in clinical research. Variants are detected through traditional immunohistochemistry, microarray or PCR panels, or large-scale next generation sequencing, either for purposes of clinical care or understanding of biological processes of carcinogenesis and cancer treatment. However, we see few variants used in standard epidemiological research in the context of rich phenotypes: longitudinal observational patient data of treatment, progression and survival. The reason for this lies in the incompatibility of data representations and methods. In a typical observational study, cohorts, exposures, and outcomes are defined through clinical events encoded by predefined concepts. Epidemiological methods use this closed system model to measure the statistical change in rates, which are calculated with the denominator of all possible clinical states. The same is very challenging for genomic variants, which work like open systems: The representation of possibly infinite variants, whether previously observed or not. The Oncology Working Group of OHDSI has been working on the development of a canonical, comprehensive, and non-redundant representation of genomic variants that are clinically relevant for cancer. The resulting reference list, provided as part of the OMOP Standardized Vocabularies, is called 'OMOP Genomic'. It was constructed by consolidating genomic variants from public somatic cancer variant knowledgebases and contains +95,000 variations from 575 cancer genes. Assessment of the current gap, integration of other genomic knowledgebases are essential to improve the coverage of important and clinically relevant mutations implicated in cancer. Precision Oncology requires the application of genomic variants to epidemiological methods used in clinical research. Variants are detected through traditional immunohistochemistry, microarray or PCR panels, or large-scale next generation sequencing, either for purposes of clinical care or understanding of biological processes of carcinogenesis and cancer treatment. However, we see few variants used in standard epidemiological research in the context of rich phenotypes: longitudinal observational patient data of treatment, progression and survival. The reason for this lies in the incompatibility of data representations and methods. In a typical observational study, cohorts, exposures, and outcomes are defined through clinical events encoded by predefined concepts. Epidemiological methods use this closed system model to measure the statistical change in rates, which are calculated with the denominator of all possible clinical states. The same is very challenging for genomic variants, which work like open systems: The representation of possibly infinite variants, whether previously observed or not. The Oncology Working Group of OHDSI has been working on the development of a canonical, comprehensive, and non-redundant representation of genomic variants that are clinically relevant for cancer. The resulting reference list, provided as part of the OMOP Standardized Vocabularies, is called 'OMOP Genomic'. It was constructed by consolidating genomic variants from public somatic cancer variant knowledgebases and contains +95,000 variations from 575 cancer genes. Assessment of the current gap, integration of other genomic knowledgebases are essential to improve the coverage of important and clinically relevant mutations implicated in cancer.

C-O-H-S fluids released by oceanic serpentinite in subduction zones: Implications for arc-magma oxidation

Subducted oceanic serpentinite carries H2O, ferric iron, carbon and sulfur into the subduction zone, where they are stepwise released during dehydration. These C-O-H-S fluids are intimately linked to magma oxidation and ore formation within magmatic arcs. However, the mechanism of transfer of carbon, sulfur and ferric iron into fluids is poorly known. It is also controversial whether the C-O-H-S fluids can oxidize arc magmas. We present new thermodynamic models for serpentinite to predict the species produced in C-O-H-S fluids during subduction. Closed system modeling provides molar concentrations of species at different P-T conditions, and shows that reducing species generally have high solubilities at low P-T conditions. Oxidizing species mainly partition into the fluid at higher P-T conditions. The concentration of iron in fluids is much lower than that of other major elements. Open-system fluid fractionation shows that only 5-14% of the carbon is lost to the mantle wedge, while the loss of sulfur is as high as 55-100% at sub-arc depths. Almost all carbon and sulfur lost are released as oxidizing species. The redox properties of the fluids are controlled by sulfur, resulting in an oxygen fugacity of the fluids that is 0.6-0.95 log units higher than the HM buffer. Sulfur loss is a function of the whole-rock composition (e.g., Mg/Si, Al, Ca, and especially Fe3+/Fetot ratio) and the geothermal gradient of the subduction zone, with elevated sulfur fluxes predicted for serpentinite in cold subduction zones. The maximum amount of sulfur released in a cold subduction regime is 5.5 times higher than in a warm subduction regime. Our modeling results are consistent with petrological observations and global-arc-basalt oxygen fugacity calculations and highlight that the C-O-H-S fluids released from the subducted slab may contribute considerably to the composition of arc magmas.

Energy Sufficiency of Biomass and Wastewater in Closed Process of Sago Starch Production

Sago grows in lowland and peat swamp regions that are relatively isolated due to limited basic infrastructures, including energy supply, especially electricity. These limitations constraining the development of sago starch production and industry. The sago starch production process generates by-products such as sago bark waste, pith waste, and wastewater which are potentially used as an energy source. This paper discusses a closed system model of an energy-independent sago starch production process from the utilization of by-products and wastewater. A mass balance model was developed to calculate the energy potency of by-products and waste to construct a closed system for the sago starch production process. The model's output showed that the by-product from processing 1,000 tons of sago stems per day with an optimal yield of 14% potentially generates 90,562 kWh of energy. This energy potency can meet the 26,070 kWh energy needed for sago starch production, making it possible to develop into a closed production system. Further research is needed to determine the site-specific aspects that affect energy sufficiency.

ANALYSIS AND FORECASTING OF THE COMMODITY MARKET SITUATION TO DETERMINE THE DIRECTIONS OF APPLICATION OF INTERNET MARKETING TOOLS IN PRODUCT PROMOTION

Objective. The objective of the article is theoretical and practical study of the factors influencing the economic situation on the marketing activities of the enterprise and product promotion, in particular, the application of the results of analysis and forecasting of the current state of the relevant product market when determining the directions for the use of Internet marketing tools. Methods. To achieve the goal, general scientific and special research methods are applied, in particular: the method of synthesis and analysis, methods of comparisons, generalizations and analogies, the method of comparative comparison and analysis of scientific publications, tabular and graphoanalytical methods. Results. As a result of the conducted theoretical and practical study of the factors of conjunctural influence on the marketing activity of the enterprise and the promotion of the product, the main directions of application of the results of the analysis and forecasting of the situation of the relevant product market are outlined when determining the directions of application of Internet marketing tools. The need to use Internet marketing tools for promoting goods and services based on preliminary analysis and forecasting of the market conditions is substantiated. The essence and prospects of the use of Internet marketing as a hybrid technology in the conditions of the modern information society are determined. The main components of Internet marketing, divided into targeted marketing, search and Internet promotion of goods, are specified. The main areas of application of digital technologies to attract and retain consumers are outlined. An algorithmic scheme of the relationship between market research and Internet marketing is proposed, which justifies the need to analyze and forecast the market conditions of the relevant product markets before using Internet marketing tools and allows presenting the entire process of marketing communications as a closed system model from the point of view of enterprise interaction and the market.

Comprehensive Study Identifies a Sensitive, Low-Risk, Closed-System Model for Detection of Fungal Contaminants in Cell and Gene Therapy Products.

The U.S. Food and Drug Administration (FDA) regulates manufacturing and testing of advanced therapeutic medicinal products (ATMPs) to ensure the safety of each product for human use. Gold-standard sterility testing (USP<71>) and alternative blood culture systems have major limitations for the detection of fungal contaminants. In this study, we evaluated the performance of iLYM (lactic acid-fermenting organisms, yeasts, and mold) medium (designed originally for the food and beverage industry) to assess its potential for use in the biopharmaceutical field for ATMP sterility testing. We conducted a parallel evaluation of four different test systems (USP<71>, BacT/Alert, Bactec, and Sabouraud dextrose agar [SDA] culture), three different bottle media formulations (iLYM, iFA Plus, and Myco/F Lytic), and two incubation temperatures (22.5°C and 32.5 to 35°C) using a diverse set of fungi (n = 51) isolated from NIH cleanroom environments and previous product contaminants. Additionally, we evaluated the effect of agitation versus delayed-entry static preincubation on test sensitivity and time to detection (TTD). Overall, delayed entry of bottles onto the BacT/Alert or Bactec instruments (with agitation) did not improve test performance. USP<71> and SDA culture continued to significantly outperform each automated culture condition alone. However, we show, for the first time, that a closed-system, dual-bottle combination of iLYM 22.5°C and iFA Plus 32.5°C can provide high fungal sensitivity, statistically comparable to USP<71>, when tested against a diverse range of environmental fungi. Our study fills a much-needed gap in biopharmaceutical testing and offers a favorable testing algorithm that maximizes bacterial and fungal test sensitivity while minimizing risk of product contamination associated with laboratory handling.

On the dynamic allocation of assets subject to failure

Motivated by situations arising in surveillance, search and monitoring, in this paper we study dynamic allocation of assets which tend to fail, requiring replenishment before once again being available for operation on one of the available tasks. We cast the problem as a closed-system continuous-time Markov decision process with impulsive controls, maximising the long-term time-average sum of per-task reward rates. We then formulate an open-system continuous-time approximative model, whose Lagrangian relaxation yields a decomposition (innovatively extending the restless bandits approach), from which we derive the corresponding Whittle index. We propose two ways of adapting the Whittle index derived from the open-system model to the original closed-system model, a naïve one and a cleverly modified one. We carry out extensive numerical performance evaluation of the original closed-system model, which indicates that the cleverly modified Whittle index rule is nearly optimal, being within 1.6% (0.4%, 0.0%) of the optimal reward rate 75% (50%, 25%) of the time, and significantly superior to uniformly random allocation which is within 22.0% (16.2%, 10.7%) of the optimal reward rate. Our numerical results also suggest that the Whittle index must be cleverly modified when adapting it from the open-system, as the naïve Whittle index rule is not superior to a myopic greedy policy.

Infiltration-driven metamorphism, New England, USA: Regional CO2 fluxes and implications for Devonian climate and extinctions

We undertake thermodynamic pseudosection modeling of metacarbonate rocks in the Wepawaug Schist, Connecticut, USA, and examine the implications for CO2 outgassing from collisional orogenic belts. Two broad types of pseudosections are calculated: (1) a fully closed-system model with no fluid infiltration and (2) a fluid-buffered model including an H2O–CO2 fluid of a fixed composition. This fluid-buffered model is used to approximate a system open to infiltration by a water-bearing fluid. In all cases the fully closed-system model fails to reproduce the observed major mineral zones, mineral compositions, reaction temperatures, and fluid compositions. The fluid-infiltrated models, on the other hand, successfully reproduce these observations when the XCO2 of the fluid is in the range ∼0.05 to ∼0.15. Fluid-infiltrated models predict significant progressive CO2 loss, peaking at ∼50% decarbonation at amphibolite facies. The closed-system models dramatically underestimate the degree of decarbonation, predicting only ∼15% CO2 loss at peak conditions, and, remarkably, <1% CO2 loss below ∼600 °C. We propagate the results of fluid-infiltrated pseudosections to determine an areal CO2 flux for the Wepawaug Schist. This yields ∼1012 mol CO2 km−2 Myr−1, consistent with multiple independent estimates of the metamorphic CO2 flux, and comparable in magnitude to fluxes from mid-ocean ridges and volcanic arcs. Extrapolating to the area of the Acadian orogenic belt, we suggest that metamorphic CO2 degassing is a plausible driver of global warming, sea level rise, and, perhaps, extinction in the mid- to late-Devonian.

Probing the Dynamics of Clot-Bound Thrombin at Venous Shear Rates

In closed system models of fibrin formation, exosite-mediated thrombin binding to fibrin contributes to clot stability and is resistant to inhibition by antithrombin/heparin while still susceptible to small, active-site inhibitors. Each molecule of fibrin can bind ∼1.6 thrombin molecules at low-affinity binding sites (Kd = 2.8 μM) and ∼0.3 molecules of thrombin at high-affinity binding sites (Kd = 0.15 μM). The goal of this study is to assess the stability of fibrin-bound thrombin under venous flow conditions and to determine both its accessibility and susceptibility to inhibition. A parallel-plate flow chamber (7 × 50 × 0.25 mm) for studying the stability of thrombin (0–1400 nM) adhered to a fibrin matrix (0.1–0.4 mg/mL fibrinogen, 10 nM thrombin) under a variety of venous flow conditions was developed using the thrombin-specific, fluorogenic substrate SN-59 (100 μM). The flow within this system is laminar (Re < 1) and reaction rates are driven by enzyme kinetics (Pe = 100, Da = 7000). A subpopulation of active thrombin remains stably adhered to a fibrin matrix over a range of venous shear rates (46–184 s−1) for upwards of 30 min, and this population is saturable at loads >500 nM and sensitive to the initial fibrinogen concentration. These observations were also supported by a mathematical model of thrombin adhesion to fibrin, which demonstrates that thrombin initially binds to the low-affinity thrombin binding sites before preferentially equilibrating to higher affinity sites. Antithrombin (2.6 μM) plus heparin (4 U/mL) inhibits 72% of the active clot-bound thrombin after ∼10 min at 92 s−1, while no inhibition is observed in the absence of heparin. Dabigatran (20 and 200 nM) inhibits (50 and 93%) clot-bound thrombin reversibly (87 and 66% recovery). This model illustrates that clot-bound thrombin stability is the result of a constant rearrangement of thrombin molecules within a dense matrix of binding sites.

Oxygen isotope trajectories of crystallizing melts: Insights from modeling and the plutonic record

Elevated oxygen isotope values in igneous rocks are often used to fingerprint supracrustal alteration or assimilation of material that once resided near the surface of the earth. The δ18O value of a melt, however, can also increase through closed-system fractional crystallization. In order to quantify the change in melt δ18O due to crystallization, we develop a detailed closed-system fractional crystallization mass balance model and apply it to six experimentally- and naturally-determined liquid lines of descent (LLDs), which cover nearly complete crystallization intervals (melt fractions of 1 to <0.1). The studied LLDs vary from anhydrous tholeiitic basalts to hydrous high-K and calc-alkaline basalts and are characterized by distinct melt temperature-SiO2 trajectories, as well as, crystallizing phase relationships. Our model results demonstrate that melt fraction-temperature-SiO2 relationships of crystallizing melts, which are strongly a function of magmatic water content, will control the specific δ18O path of a crystallizing melt. Hydrous melts, typical of subduction zones, undergo larger increases in δ18O during early stages of crystallization due to their lower magmatic temperatures, greater initial increases in SiO2 content, and high temperature stability of low δ18O phases, such as oxides, amphibole, and anorthitic plagioclase (versus albite). Conversely, relatively dry, tholeiitic melts only experience significant increases in δ18O at degrees of crystallization greater than 80%. Total calculated increases in melt δ18O of 1.0–1.5‰ can be attributed to crystallization from ∼50 to 70wt.% SiO2 for modeled closed-system crystallizing melt compositions. As an example application, we compare our closed system model results to oxygen isotope mineral data from two natural plutonic sequences, a relatively dry, tholeiitic sequence from the Upper and Upper Main Zones (UUMZ) of the Bushveld Complex (South Africa) and a high-K, hydrous sequence from the arc-related Dariv Igneous Complex (Mongolia). These two sequences were chosen as their major and trace element compositions appear to have been predominantly controlled by closed-system fractional crystallization and their LLDs have been modeled in detail. We calculated equilibrium melt δ18O values using the measured mineral δ18O values and calculated mineral-melt fractionation factors. Increases of 2–3‰ and 1–1.5‰ in the equilibrium melts are observed for the Dariv Igneous Complex and the UUMZ of the Bushveld Complex, respectively. Closed-system fractional crystallization model results reproduce the 1‰ increase observed in the equilibrium melt δ18O for the Bushveld UUMZ, whereas for the Dariv Igneous Complex assimilation of high δ18O material is necessary to account for the increase in melt δ18O values. Assimilation of evolved supracrustal material is also confirmed with Sr and Nd isotope analyses of clinopyroxene from the sequence. Beginning with a range of mantle-derived basalt δ18O values of 5.7‰ (“pristine” mantle) to ∼7.0‰ (heavily subduction-influenced mantle), our model results demonstrated that high-silica melts (i.e. granites) with δ18O of up to 8.5‰ can be produced through fractional crystallization alone. Lastly, we model the zircon-melt δ18O fractionations of different LLDs, emphasizing their dependence on the specific SiO2-T relationships of a given crystallizing melt. Wet, relatively cool granitic melts will have larger zircon-melt fractionations, potentially by ∼1.5‰, compared to hot, dry granites. Therefore, it is critical to constrain zircon-melt fractionations specific to a system of interest when using zircon δ18O values to calculate melt δ18O.

Fluid evolution in CM carbonaceous chondrites tracked through the oxygen isotopic compositions of carbonates

The oxygen isotopic compositions of calcite grains in four CM carbonaceous chondrites have been determined by NanoSIMS, and results reveal that aqueous solutions evolved in a similar manner between parent body regions with different intensities of aqueous alteration. Two types of calcite were identified in Murchison, Mighei, Cold Bokkeveld and LaPaz Icefield 031166 by differences in their petrographic properties and oxygen isotope values. Type 1 calcite occurs as small equant grains that formed by filling of pore spaces in meteorite matrices during the earliest stages of alteration. On average, the type 1 grains have a δ18O of ∼32–36‰ (VSMOW), and Δ17O of between ∼2‰ and −1‰. Most grains of type 2 calcite precipitated after type 1. They contain micropores and inclusions, and have replaced ferromagnesian silicate minerals. Type 2 calcite has an average δ18O of ∼21–24‰ (VSMOW) and a Δ17O of between ∼−1‰ and −3‰. Such consistent isotopic differences between the two calcite types show that they formed in discrete episodes and from solutions whose δ18O and δ17O values had changed by reaction with parent body silicates, as predicted by the closed-system model for aqueous alteration. Temperatures are likely to have increased over the timespan of calcite precipitation, possibly owing to exothermic serpentinisation. The most highly altered CM chondrites commonly contain dolomite in addition to calcite. Dolomite grains in two previously studied CM chondrites have a narrow range in δ18O (∼25–29‰ VSMOW), with Δ17O ∼−1‰ to −3‰. These grains are likely to have precipitated between types 1 and 2 calcite, and in response to a transient heating event and/or a brief increase in fluid magnesium/calcium ratios. In spite of this evidence for localised excursions in temperature and/or solution chemistry, the carbonate oxygen isotope record shows that fluid evolution was comparable between many parent body regions. The CM carbonaceous chondrites studied here therefore sample either several parent bodies with a very similar initial composition and evolution or, more probably, a single C-type asteroid.

Silicon isotope and silicic acid uptake in surface waters of Marguerite Bay, West Antarctic Peninsula

The silicon isotope composition (δ30Si) of dissolved silicon (DSi) and biogenic silica (BSi) provides information about the silicon cycle and its role in oceanic carbon uptake in the modern ocean and in the past. However, there are still questions outstanding regarding the impact of processes such as oceanic mixing, export and dissolution on the isotopic signature of seawater, and the impacts on sedimentary BSi. This study reports the δ30Si of DSi from surface waters at the Rothera Time Series (RaTS) site, Ryder Bay, in a coastal region of the West Antarctic Peninsula (WAP). The samples were collected at the end of austral spring through the end of austral summer/beginning of autumn over two field seasons, 2004/5 and 2005/6. Broadly, for both field seasons, DSi diminished and δ30Si of DSi increased through the summer, but this was accomplished during only a few short periods of net nutrient drawdown. During these periods, the δ30Si of DSi was negatively correlated with DSi concentrations. The Si isotope fractionation factor determined for the net nutrient drawdown periods, ɛuptake, was in the range of −2.26 to −1.80‰ when calculated using an open system model and −1.93 to −1.33‰ when using a closed system model. These estimates of ɛ are somewhat higher than previous studies that relied on snapshots in time rather than following changes in δ30Si and DSi over time, which therefore were more likely to include the effects of mixing of dissolved silicon up into the mixed layer. Results highlight also that, even at the same station and within a single growing season, the apparent fractionation factor may exhibit significant temporal variability because of changes in the extent of biological removal of DSi, nutrient source, siliceous species, and mixing events.Paleoceanographic studies using silicon isotopes need careful consideration in the light of our new results.

Role of crustal assimilation and basement compositions in the petrogenesis of differentiated intraplate volcanic rocks: a case study from the Siebengebirge Volcanic Field, Germany

The Siebengebirge Volcanic Field (SVF) in western Germany is part of the Cenozoic Central European Volcanic Province. Amongst these volcanic fields, the relatively small SVF comprises the entire range from silica-undersaturated mafic lavas to both silica-undersaturated and silica-saturated differentiated lavas. Owing to this circumstance, the SVF represents a valuable study area representative of intraplate volcanism in Europe. Compositions of the felsic lavas can shed some new light on differentiation of intraplate magmas and on the extent and composition of potential crustal assimilation processes. In this study, we provide detailed petrographic and geochemical data for various differentiated SVF lavas, including major and trace element concentrations as well as Sr–Nd–Hf–Pb isotope compositions. Samples include tephriphonolites, latites, and trachytes with SiO2 contents ranging between 53 and 66 wt%. If compared to previously published compositions of mafic SVF lavas, relatively unradiogenic 143Nd/144Nd and 176Hf/177Hf coupled with radiogenic 87Sr/86Sr and 207Pb/204Pb lead to the interpretation that the differentiated volcanic rocks have assimilated significant amounts of lower crustal mafic granulites like the ones found as xenoliths in the nearby Eifel volcanic field. These crustal contaminants should possess unradiogenic 143Nd/144Nd and 176Hf/177Hf, radiogenic 87Sr/86Sr, and highly radiogenic 207Pb/204Pb compositions requiring the presence of ancient components in the central European lower crust that are not sampled on the surface. Using energy-constrained assimilation–fractional crystallisation (EC-AFC) model calculations, differentiation of the SVF lithologies can be modelled by approximately 39–47 % fractional crystallisation and 6–15 % crustal assimilation. Notably, the transition from silica-undersaturated to silica-saturated compositions of many felsic lavas in the SVF that is difficult to account for in closed-system models is also well explained by such amounts of crustal assimilation.

The influence of the biological pump on ocean chemistry: implications for long-term trends in marine redox chemistry, the global carbon cycle, and marine animal ecosystems.

The net export of organic matter from the surface ocean and its respiration at depth create vertical gradients in nutrient and oxygen availability that play a primary role in structuring marine ecosystems. Changes in the properties of this ‘biological pump’ have been hypothesized to account for important shifts in marine ecosystem structure, including the Cambrian explosion. However, the influence of variation in the behavior of the biological pump on ocean biogeochemistry remains poorly quantified, preventing any detailed exploration of how changes in the biological pump over geological time may have shaped long‐term shifts in ocean chemistry, biogeochemical cycling, and ecosystem structure. Here, we use a 3‐dimensional Earth system model of intermediate complexity to quantitatively explore the effects of the biological pump on marine chemistry. We find that when respiration of sinking organic matter is efficient, due to slower sinking or higher respiration rates, anoxia tends to be more prevalent and to occur in shallower waters. Consequently, the Phanerozoic trend toward less bottom‐water anoxia in continental shelf settings can potentially be explained by a change in the spatial dynamics of nutrient cycling rather than by any change in the ocean phosphate inventory. The model results further suggest that the Phanerozoic decline in the prevalence ocean anoxia is, in part, a consequence of the evolution of larger phytoplankton, many of which produce mineralized tests. We hypothesize that the Phanerozoic trend toward greater animal abundance and metabolic demand was driven more by increased oxygen concentrations in shelf environments than by greater food (nutrient) availability. In fact, a lower‐than‐modern ocean phosphate inventory in our closed system model is unable to account for the Paleozoic prevalence of bottom‐water anoxia. Overall, these model simulations suggest that the changing spatial distribution of photosynthesis and respiration in the oceans has exerted a first‐order control on Earth system evolution across Phanerozoic time.

N2O source partitioning in soils using (15)N site preference values corrected for the N2O reduction effect.

The aim of this study was to determine the impact of isotope fractionation associated with N2O reduction during soil denitrification on N2O site preference (SP) values and hence quantify the potential bias on SP-based N2O source partitioning. The N2O SP values (n = 431) were derived from six soil incubation studies in N2-free atmosphere, and determined by isotope ratio mass spectrometry (IRMS). The N2 and N2O concentrations were measured directly by gas chromatography. Net isotope effects (NIE) during N2O reduction to N2 were compensated for using three different approaches: a closed-system model, an open-system model and a dynamic apparent NIE function. The resulting SP values were used for N2O source partitioning based on a two end-member isotopic mass balance. The average SP0 value, i.e. the average SP values of N2O prior to N2O reduction, was recalculated with the closed-system model, resulting in -2.6 ‰ (±9.5), while the open-system model and the dynamic apparent NIE model gave average SP0 values of 2.9 ‰ (±6.3) and 1.7 ‰ (±6.3), respectively. The average source contribution of N2O from nitrification/fungal denitrification was 18.7% (±21.0) according to the closed-system model, while the open-system model and the dynamic apparent NIE function resulted in values of 31.0% (±14.0) and 28.3% (±14.0), respectively. Using a closed-system model with a fixed SP isotope effect may significantly overestimate the N2O reduction effect on SP values, especially when N2O reduction rates are high. This is probably due to soil inhomogeneity and can be compensated for by the application of a dynamic apparent NIE function, which takes the variable reduction rates in soil micropores into account.

Geochemistry of the late Holocene rocks from the Tolbachik volcanic field, Kamchatka: Quantitative modelling of subduction-related open magmatic systems

We present new major and trace element, high-precision Sr-Nd-Pb (double spike), and Oisotope data for the whole range of rocks from the Holocene Tolbachik volcanic field in the Central Kamchatka Depression (CKD). The Tolbachik rocks range from high-Mg basalts to low-Mg basaltic trachyandesites. The rocks considered in this paper represent mostly Late Holocene eruptions (using tephrochronological dating), including historic ones in 1941, 1975-1976 and 2012-2013. Major compositional features of the Tolbachik volcanic rocks include the prolonged predominance of one erupted magma type, close association of middle-K primitive and high-K evolved rocks, large variations in incompatible element abundances and ratios but narrow range in isotopic composition. We quantify the conditions of the Tolbachik magma origin and evolution and revise previously proposed models. We conclude that all Tolbachik rocks are genetically related by crystal fractionation of medium-K primary magmas with only a small range in trace element and isotope composition. The primary Tolbachik magmas contain ~14 wt% MgO and ~4% wt% H2O and originated by partial melting (~6%) of moderately depleted mantle peridotite with Indian-MORB-type isotopic composition at temperature of ~1250oC and pressure of ~2 GPa. The melting of the mantle wedge was triggered by slab-derived hydrous melts formed at ~2.8 GPa and ~725oC from a mixture of sediments and MORB- and Meiji- type altered oceanic crust. The primary magmas experienced a complex open-system evolution termed Recharge-Evacuation-Fractional Crystallization (REFC). First the original primary magmas underwent open-system crystal fractionation combined with periodic recharge of the magma chamber with more primitive magma, followed by mixing of both magma types, further fractionation and finally eruption. Evolved high-K basalts, which predominate in the Tolbachik field, and basaltic trachyandesites erupted in 2012-2013 approach steady-state REFC liquid compositions at different eruption or replenishment rates. Intermediate rocks, including high-K, high-Mg basalts, are formed by mixing of the evolved and primitive magmas. Evolution of Tolbachik magmas is associated with large fractionation between incompatible trace elements (e.g., Rb/Ba, La/Nb, Ba/Th) and is strongly controlled by the relative difference in partitioning between crystal and liquid phases. The Tolbachik volcanic field shows that open-system scenarios provide more plausible and precise descriptions of long-lived arc magmatic systems than simpler, but often geologically unrealistic, closed-system models.

Subduction zone metamorphic pathway for deep carbon cycling: II. Evidence from HP/UHP metabasaltic rocks and ophicarbonates

Exposures of low-grade metabasalts and ophicarbonates in the Northern Apennines, and their high- and ultrahigh-pressure metamorphic equivalents in the Western and Ligurian Alps and Tianshan (representing an overall peak P–T range of ~0.2–3.0GPa, 200–610°C), allow investigation of the effects of prograde metamorphic devolatilization, and other fluid–rock interactions, on degrees of retention and isotopic evolution of C in subducting oceanic crust and associated mantle rocks. Such work can inform models of C cycling at convergent margins, helping to constrain the efficiency of return of initially subducted C via arc volcanism and the fraction of this subducted C entering the deeper mantle beyond arcs.In the metabasaltic rocks, the preservation of finely disseminated carbonate with δ13C overlapping that of seafloor-altered protoliths, and the minimal mineralogical evidence of decarbonation, indicates large degrees of carbonate retention in this suite extending to UHP conditions similar to those beneath modern volcanic fronts. For many of the metabasalts, the δ18O of this carbonate can be explained by closed-system equilibration with silicate phases (e.g., garnet, clinopyroxene) during HP/UHP metamorphism. Larger volumes of carbonate preserved in interpillow regions and as breccia-filling largely escaped decarbonation, showing little or no evidence for reaction with adjacent metabasalt. Calculated devolatilization histories demonstrate that, in a closed-system model, carbonate in metabasaltic rocks can largely be preserved to depths approaching those beneath volcanic fronts (80–90km). Modeling of open-system behavior indicates that episodic infiltration of such rocks by H2O-rich fluids would have greatly enhanced decarbonation. Trends in O–C isotope composition of carbonate in some metabasaltic suites likely reflect effects of infiltration by externally-derived fluid with or without resulting decarbonation. Most carbonated ultramafic rocks similarly show little mineralogical evidence for decarbonation, consistent with calculated reaction histories, and have δ13C largely overlapping that of seafloor equivalents. However, the high-grade ophicarbonates show more restricted ranges in δ18O consistent with some control by infiltrating fluids, likely during subduction.This combination of field, petrographic, and isotopic evidence, together with calculated decarbonation histories, is consistent with minimal loss of CO2 from these rocks via decarbonation during forearc metamorphism. Combining our results with those of Cook-Kollars et al. (2014; Chemical Geology) for associated W. Alps metasedimentary rocks, we suggest that the majority of the CO2 (perhaps 80–90%, considering the full range of rock types) could be retained through forearcs in more intact volumes of subducting sediment, basalt, and ophicarbonate experiencing closed- or limited open-system conditions. Deep in forearcs and beneath arcs, decarbonation (and also carbonate dissolution) could be enhanced in shear zones and highly fractured volumes experiencing larger fluid flux in part from dehydrating sub-crustal ultramafic rocks in slabs. Degrees of C loss by decarbonation, carbonate dissolution, and partial melting should be particularly significant as the subducting sections experience heating to >600°C at depths of 80–120km (i.e., approximately at depths beneath arcs).