Guangzhou Institute of Geochemistry
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Rubidium Isotope Measurements of Low-Rb Geological Materials by MC-ICP-MS
No full textThe rubidium (Rb) isotope system has the potential to trace planetary evolution, magmatic-fluid interaction and chemical weathering. These applications are based on Rb isotope measurement results with precisions fit for purpose, but measurements of low-Rb geological materials are challenging due to large sample consumption and overload of ion-exchange resin. Here we developed a measurement procedure for Rb isotope data (delta 87RbSRM984) of low-Rb geological materials using MC-ICP-MS. Using an Aridus III desolvator and Ni standard sampler + Ni X skimmer cone combination, the Rb loading amount was reduced significantly to 20 ng. A comparison between two methods for instrumental mass-bias correction, the sample-standard bracketing and combined sample-standard bracketing and internal (Zr) normalisation (C-SSBIN), shows that C-SSBIN could produce Rb isotope data with better intermediate measurement precisions but strictly restricted to optimal Zr/Rb ratio. The robustness of this method was demonstrated by monitoring delta 87RbSRM984 data of two in-house Rb isotope standards, replicates, some reference materials with delta 87RbSRM984 values previously reported, and element-doped and matrix-spiked synthetic solutions. Based on repeated measurements of Rb isotope standards and reference materials, the long-term (over one year) intermediate precision was better than 0.05 parts per thousand (2s, standard deviations). We additionally recommend thirteen reliable reference materials for future Rb isotope ratio measurements
Can the Artificial Release of Fluorinated Gases Offset Global Cooling Due to Supervolcanic Eruptions?
No full textLarge volcanic eruptions, such as the prehistoric Yellowstone eruption, induce abrupt global cooling-by some estimates at a rate of similar to 1 degrees C/year, lasting for more than a decade. An abrupt global cooling of several degrees C-even if only lasting a few years-would present immediate, drastic stress on biodiversity and food production. This cooling poses a global catastrophic risk to human society beyond the immediate and direct impact of eruptions. Using a simple climate model, this paper discusses the possibility of counteracting large volcanic cooling with the intentional release of greenhouse gases. Longer-lived compounds (e.g., CO2 and CH4) are unsuitable for this purpose, but selected fluorinated gases (F-gases), either individually or in combinations, could be released at gigaton scale to offset large volcanic cooling substantially. We identify candidate F-gases (e.g., C4F6 and CH3F) and derive radiative and chemical properties of 'ideal' compounds matching specific cooling events. Geophysical constraints on manufacturing and stockpiling due to mineral availability are considered, alongside technical and economic implications based on present-day market assumptions. The effects and uncertainty due to atmospheric chemistry related to aerosol injection, F-gases release, and solar dimming are discussed in the context of large volcanic perturbation. The caveats and future steps using more complex chemistry-climate models are discussed. Despite the speculative nature of the magnitude and composition of F-gases, our conceptual analysis has implications for testing the possibility of mitigating certain global catastrophic cooling risks (e.g., nuclear winter, asteroid impact, and glacier transition) via intentional intervention
Sedimentary facies controlled biogeochemical process of biotic extinction and turnover across the Cambrian SPICE event
No full textThe Steptoean positive carbon isotope excursion (SPICE) event, one of the largest carbon cycle perturbations in the Cambrian, coincides with shallow-shelf-fauna extinction and plankton revolution (critical transition of plankton). The event is globally documented, but biogeochemical responses of these biotic evolutions in varying facies environments are not well understood. Here high-resolution paired delta 18Ocarb, delta 13Ccarb and delta 13Corg datasets from varied paleodepth environments in the Tarim Basin, NW China reveal facies-dependent signatures of the event, with globally synchronous patterns but notable intra-basinal variability. Shallow marine facies record the end-Marjuman extinction with a distinct negative delta 13Corg excursion prior to the event, while the transitional facies region marks twice positive delta 13C excursions corresponding to an asynchronous plankton revolution from shallow and deep areas during the event. The varying isotope responses are interpreted in the context of primary productivity and redox conditions, with deeper basins recording more 13C enriched signals (i.e., higher delta 13C) due to greater organic matter preservation under anoxic conditions, compared to the platform area. The biotic extinction, the planktonic revolution and the interaction of organisms along the shallow to deep marine depth gradient were reflected by the significant isotopic shifts recorded during the event, suggesting depth-dependent biogeochemical processes that shaped marine ecosystems.
Biogeochemical responses to one of the largest carbon cycle perturbations taking place 497 to 494 million years ago, show variability within sedimentary basins and reflect primary productivity and redox conditions, according to high-resolution carbon and oxygen isotope analyses from the Tarim Basin, China
Zinc partitioning between mantle minerals and basaltic melts: Application to revisit the Zn/Fe<SUP>T</SUP> redox proxy
No full textZn/Fe-T (Fe-T=Fe2+ + Fe3+) ratios in primitive melts have been proposed as a redox proxy to assess the redox states of the upper mantle. However, to effectively use the melt Zn/Fe-T ratio as a redox proxy, it is necessary to compare variations of melt Zn/Fe-T ratios induced by changes in oxygen fugacity (fO(2)) with variations due to changes in Zn-Fe contents and mineralogy of the sources. Here we show that the melt Zn/Fe-T ratio variation caused by fO(2) change can be expressed as Delta(Zn-m/FemT) = (Zn-per/Fe-per(T))* Delta(Fe-m(2+)/Fe-m(T))/(D-Zn(per/m)/D-Fe(2+per/m)). Zn/Fe-T ratios in most arc and MORB peridotites (Zn-per/Fe-per(T)) are 9.0 +/- 1.0*10(-4), and melt Fe2+/Fe-T ratio variation resulted from fO(2) change [Delta(Fe-m(2+)/Fe-m(T))] can be easily obtained by the existing model. Hence, if the Zn and Fe2+ partition coefficients (D-Zn(per/m) and D-Fe(2+per/m)) between melt and peridotite are known, the melt Zn/Fe-T ratio variation resulting from fO(2) change can be estimated. In this study, we determined D-Zn between olivine, orthopyroxene, clinopyroxene and basaltic melts at 0.75-2.5 GPa and 1250-1450 degrees C. Our data show that melt composition (expressed as MgO content) dominantly controls the mineral-melt Zn partitioning under peridotite melting conditions. These data, along with published mineral-melt D-Fe(2+) data, enable us to calculate appropriate D-Zn(per/m)/D-Fe(2+per/m), which is 0.78 +/- 0.02 under arc and MORB spinel peridotite melting conditions. Based on these parameters, the calculated average melt Zn/Fe-T ratio variation caused by per log unity fO(2) change in typical fO(2) span of arc and MORB mantles is only similar to 0.69 +/- 0.20*10(-4). Alternatively, melt Zn/Fe-T ratio variations caused by changes in Zn-Fe contents and mineralogy of peridotites are +/- 1.10*10(-4). These findings indicate that melt Zn/Fe-T ratio variation induced by one log units fO(2) change is on the same order of magnitude as those caused by changes in Zn-Fe contents and mineralogy of peridotites. Therefore, unless the precise chemical and mineralogical compositions of the mantle sources can be determined independently, the melt Zn/Fe-T redox proxy is unsuitable for tracing the mantle fO(2). Our study, combined with recent works on melt Cu and V/Sc redox proxies, suggests that these redox proxies, previously considered as the strongest evidence for a reduced arc mantle, might not support the idea of a reduced arc mantle
Dissolved Aluminum Measurement Methods and Their Application in Atmospheric Aerosol Research
No full textAtmospheric deposition of desert dust aerosol is a major source of key nutrients for surface seawater in open oceans, significantly impacting marine biogeochemistry and primary productivity. As a tracer for desert dust aerosol, aluminum (Al) is widely used to estimate deposition fluxes of desert dust aerosol into the oceans, and dissolved Al concentrations in surface seawater and aerosol particles are key parameters for using this method to estimate desert dust deposition fluxes into the oceans. In this paper, we first review separation, extraction and detection methods used to measure dissolved Al in seawater and aerosol samples, and discuss their principles, advantages, limitations and applicability. After advances in aerosol Al solubility are systematically reviewed, we point out that the uncertainties in aerosol Al solubility are the bottleneck which currently limits accurate estimations of desert dust deposition fluxes into the oceans, and further analyze the sources of these uncertainties. In the final, we also outline research directions for dissolved Al analysis and aerosol Al solubility research
Terrestrial response to the Early Cretaceous Weissert Event: Insights from carbon isotope records of organic matter and leaf wax<i> n</i>-alkanes in an inland East Asian lake
No full textThe Weissert Event (WE), a significant Early Cretaceous environmental disruption, is recognized globally in marine carbonate records for its positive carbon isotope excursion (CIE), organic matter (OM) enrichment, and widespread anoxia. However, records of its terrestrial impact are sparse. This study examines carbon isotope compositions (delta 13C) from the lacustrine facies of North China's Dabeigou Formation (Yushuxia section, Luanping Basin). The synchronous positive CIEs of total organic carbon (TOC) and C 27 -C 31 n-alkanes within Members 2 to 3 of the Dabeigou Formation corroborate the Weissert Event, marking its first terrestrial observation in North China. Ratios of the isoprenoids pristane and phytane (Pr/Ph), Corg/P ratios and enrichment factors (EFs) of redox-sensitive trace metals (Mo and U) indicate transient anoxic conditions within a mainly oxic-suboxic setting from the late Valanginian to early Hauterivian, which were unfavorable for OM preservation. This highlights that although a global positive CIE occurred during the Weissert Event, anoxia and/or high TOC deposition in inland lakes were not inherent features
Compositional differences of near-critical petroleum from closed pores to wellhead in Gulong shale oil play, Songliao Basin, NE China
No full textThe Gulong shale oil play located in northern Songliao Basin is a promising exploration target in China. Member 1 of Qingshankou Formation (Well H) with high thermal maturity was preferred to obtain pressure-retained cores, long-time exposed cores, and produced petroleum (crude oil and gas). The selected samples were subjected to sequential extraction, GC, GC-MS, thermal desorption-gas chromatography (TD-GC) and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) analysis. The compositional differences of insitu fluids, residual bitumen trapped in open, confined, and closed pores, as well as wellstream, were systematically investigated. (1) In-situ fluid compositions, with a 30.8% proportion of nC1_ 5 in n-alkanes, were studied by TD-GC analysis on pressure-retained cores. Interestingly, limited amounts of C8- compounds were detected in long-time exposed bulk cores but were almost absent in exposed powder. Primally poor pore connectivity and partially adsorption or absorption of organic matter contribute to the retention of gaseous hydrocarbons. (2) Sequential extraction is a best method for obtaining compositions of fluid in pores with variable sizes. Aliphatic compounds of residual bitumen trapped in open pores are similar to those in confined pores, while polar compounds are more enriched in confined and closed pores. Originally connected pores in early oil window, has turned into confined or closed pores by compaction and cementation with increasing depth. (3) Wellstream compositions are significantly different from in-situ fluid compositions, especially in shale oil extraction. The proportion of gaseous hydrocarbons in the wellstream (76.2%) is considerably higher than that of in-situ fluids (34.1%). Comparison of aromatic hydrocarbons indicated that the wellstream is sourced from free fluids and partially adsorbed hydrocarbons in open pores. (4) Nitrogen and oxide compounds with a higher degree of condensation (higher DBE value) have poor movability, leading to extremely low content or even absence in crude oil. The compositional differences from in-situ fluids to the wellbore through the stimulated fractures are caused by selective adsorption of pore walls, confinement effect of nanopores and fluid phase changing. This study provides a window to the compositional differences of fluids released from different occurrence spaces and confirms compounds heterogeneity
Formation of reactive nitrogen species promoted by iron ions through the photochemistry of a neonicotinoid insecticide
No full textNitrous acid (HONO) and nitrogen oxides (NOx=NO+NO2) are important atmospheric pollutants and key intermediates in the global nitrogen cycle, but their sources and formation mechanisms are still poorly understood. Here, we investigated the effect of soluble iron (Fe3+) on the photochemical behavior of a widely used neonicotinoid (NN) insecticide, nitenpyram (NPM), in the aqueous phase. The yields of HONO and NOx increased significantly when NPM solution was irradiated in the presence of iron ions (Fe3+). We propose that the enhanced HONO and NO2 emissions from the photodegradation of NPM in the presence of iron ions result from the redox cycle between Fe3+ and Fe2+ and the generated reactive oxygen species (ROS) by electron transfer between the excited triplet state of NPM and molecular oxygen (O2). Using the laboratory-derived parameterization based on kinetic data and gridded downward solar radiation, we estimate that the photochemistry of NPM induced by Fe3+ releases 0.50 and 0.77 TgNyr-1 of NOx and HONO, respectively, into the atmosphere.This study suggests a novel source of HONO and NOx during daytime and potentially helps to narrow the gap between field observations and model outcomes of HONO in the atmosphere. The suggested photochemistry of NPM can be an important contribution to the global nitrogen cycle affecting the atmospheric oxidizing capacity and climate change
Transition metals in alkaline Lost City vent fluids are sufficient for early-life metabolisms
No full textDespite the importance of alkaline seafloor hydrothermal vents in broadening our understanding of deep-sea hydrothermal ecosystems, little is known about the mobility and concentrations of micronutrient transition metals in these environments. Here, we present new analyses of micronutrient transition metal concentrations in vent fluids from the iconic Lost City Hydrothermal Field (LCHF) and report concentrations of Fe = 2.9-18.3 mu mol/kg, Zn = 1.30-5.86 mu mol/kg, Cu = 0.43-5.06 mu mol/kg, Ni = 86.4-556 nmol/kg, Mn = 8.3-274 nmol/kg, V = 25.9-127 nmol/kg, Mo = 24-94 nmol/kg, Co = 8.0-135 nmol/kg, W = 4.8-16 nmol/kg, and Cd = 1.7-4.5 nmol/kg. We additionally present results of a hydrothermal lherzolite alteration experiment conducted at 300 degrees C, 500 bar. Transition metal concentrations and major chemical parameters of experimental reaction fluids are broadly similar to LCHF vent fluids, indicating that transition metal concentrations in LCHF vent fluids, and alkaline hydrothermal fluids more generally, reflect metal solubility controlled by underlying rock-buffered hydrothermal reactions. Concentrations of Ni and Mo are especially noteworthy because of their recognized importance for biological methanogenesis (Ni) and nitrogen fixation (Mo). When compared with known biological thresholds, our findings indicate that Ni concentrations in LCHF vent fluids are sufficient to support the robust methane-metabolizing microbial communities observed in the immediate vicinity of LCHF vents and suggest that Ni availability influences the spatial distribution of LCHF methanogens. Furthermore, our laboratory hydrothermal experiments demonstrate that Mo concentrations of similar magnitude to those observed in LCHF vent fluids (and also modern seawater) can be obtained by hydrothermal alteration of ultramafic rocks with Mo-free (Na, Ca) Cl aqueous solution. Thus, we conclude that alkaline hydrothermal fluids were likely similarly enriched in Mo prior to oxidation of the Earth's atmosphere and ocean, providing localized Mo-rich geochemical environments capable of supporting Mo-dependent nitrogen fixation at currently recognized threshold concentrations
Rapid Analysis of Commonly Used Quaternary Ammonium Compounds in Soil and Sediment by Ultrasonic-assited Extraction
No full textQuaternary ammonium compounds (QACs) are widely used as fungicides and surfactants in daily products and disinfection products, and as additives in industrial process. The QACs can be deposited and accumulated in soil after long-term discharge. In the present study, based on ultrasonic-assisted extraction-liquid chromatography- tandem mass spectrometry (UAE-LC-MS/MS) technique, a sensitive analytical method was developed for rapid analysis of 11 kinds of QACs, including 4 kinds of benzylalkyldimethylammonium compounds, 4 kinds of alkyltrimethylammonium compounds, and 3 kinds of dialkyldimethylammonium compounds. The results showed that QACs in soil and sediment could be effectively extracted with 5% acetonitrile at 60 degrees C . The 11 kinds of QACs were baseline-separated on a ZORBAX SB-C18 column coupled with ternary mobile phases (0.1% formic- water, 0.1% formic-methanol and 0.1% formic-acetonitrile), showing excellent linear relationship in the range of 0.001-0.5 mu g/mL (R-2>0.9776). The limits of detection were 0.01-0.31 ng/g (S/N=3). The recoveries of 11 kinds of QACs in soil samples were 78.7%-99.3% with relative standard deviations (RSDs)<12.9%, showing acceptable recoveries and repeatability. The results indicated that QACs could be extracted and cleaned-up within 4 h using this analytical method, with small volume of organic solvent consumed and less consumables materials