Secular variation of iron isotopes in north atlantic deep water

Paleo-marine redox environment fluctuation during the early Cambrian: Insight from iron isotope in the Tarim Basin, China

The Ediacaran to Cambrian period is generally considered to be the vital transition in the history of marine redox environment and life evolution on earth. The ocean oxygenation levels during this transition period are still debated. Since iron is widely involved in biogeochemical cycles and undergoes redox cycling both in the seawater and sediments, it has become a significant proxy to reconstruct paleo-marine environment. In order to constrain the paleo-marine redox state in the early Cambrian, the iron isotope composition of bulk rock (δ56FeT) is interpreted combining with iron-speciation, redox sensitive elements and pyrite sulfur isotope (δ34Spy) of Yuertusi Formation in Tarim Block. The δ56FeT values varies from -0.39 ‰ to 0.48 ‰, with an average of 0.07 ‰, mainly controlled by pyrite mineral facies in this study. Based on the mechanism of pyrite generation in different redox condition, it is proposed that the marine environment of the lower Cambrian in the Tarim basin is dominated by anoxic with intermittent euxinic state. The dynamic evolution of redox environment can be divided into three intervals. The gradual decrease of δ56Fe in Interval I indicates the paleo-marine environment changed from anoxic ferruginous to euxinic, and the paleo-marine sulfate reservoir decreased to a limited level, which might be attributed to abundant burial of organic matter and pyrite. For Interval II, δ56Fe values first increase to evident positive because of partial oxidization then decreased to that of seawater (about 0 ‰) due to complete oxidization. In Interval III, the continuous decrease of δ56Fe values infers a sustaining oxidization. In summary, the paleo-marine environment of the lower Cambrian Yuertusi Formation evolved from anoxic ferruginous to euxinic and then oxidized continuous. Iron isotope statistics from geological historical periods indicate that seawater was relatively oxidized after the NOE event but did not reach the oxidation levels of present-day seawater.

Novel Insights into Marine Iron Biogeochemistry from Iron Isotopes

The micronutrient iron plays a major role in setting the magnitude and distribution of primary production across the global ocean. As such, an understanding of the sources, sinks, and internal cycling processes that drive the oceanic distribution of iron is key to unlocking iron's role in the global carbon cycle and climate, both today and in the geologic past. Iron isotopic analyses of seawater have emerged as a transformative tool for diagnosing iron sources to the ocean and tracing biogeochemical processes. In this review, we summarize the end-member isotope signatures of different iron source fluxes and highlight the novel insights into iron provenance gained using this tracer. We also review ways in which iron isotope fractionation might be used to understand internal oceanic cycling of iron, including speciation changes, biological uptake, and particle scavenging. We conclude with an overview of future research needed to expand the utilization of this cutting-edge tracer.

Fe Isotopic Compositions of Modern Seafloor Hydrothermal Systems and Their Influence Factors

Based on previous research on the Fe isotope compositions of various components and systems of the Earth, this study focused on the Fe isotope compositions of hydrothermal systems, including the Fe isotope variations in chalcopyrite, pyrite, and sphalerite, and their possible controlling factors. The main findings are as follows: (1) The range of Fe isotopes in hydrothermal systems at mid-ocean ridge is very large. The δ56Fe values of hydrothermal fluids are characterized by significant enrichment in light Fe isotopes. (2) The δ56Fe values of sulfides also exhibit lighter Fe isotope characteristics than those of hydrothermal fluids from hydrothermal vent fields at mid-ocean ridge. The vent temperature, fluid properties, and mineral deposition processes significantly affect the δ56Fe values of hydrothermal sulfides. (3) Chalcopyrite is preferentially enriched in heavy Fe isotopes, whereas sphalerite and pyrite are enriched in light Fe isotopes. In addition, the δ56Fe values of pyrite/marcasite display a larger range than those of chalcopyrite. This pattern is directly related to equilibrium fractionation or kinetic fractionation of Fe isotopes during the deposition of sulfides. To better understand the Fe isotope compositions of modern seafloor hydrothermal systems, the geochemical behavior and fractionation mechanisms of Fe isotopes require further in situ study.

High-precision determination of the isotopic composition of dissolved iron in iron depleted seawater by double spike multicollector-ICPMS

This work demonstrates the feasibility of the measurement of the isotopic composition of dissolved iron in seawater for an iron concentration range, 0.05-1 nmol L(-1), allowing measurements in most oceanic waters, including Fe depleted waters of high nutrient low chlorophyll areas. It presents a detailed description of our previously published protocol, with significant improvements on detection limit and blank contribution. Iron is preconcentrated using a nitriloacetic acid superflow resin and purified using an AG 1-x4 anion exchange resin. The isotopic ratios are measured with a multicollector-inductively coupled plasma mass spectrometer (MC-ICPMS) Neptune, coupled with a desolvator (Aridus II or Apex-Q), using a (57)Fe-(58)Fe double spike mass bias correction. A Monte Carlo test shows that optimum precision is obtained for a double spike composed of approximately 50% (57)Fe and 50% (58)Fe and a sample to double spike quantity ratio of approximately 1. Total procedural yield is 91 +/- 25% (2SD, n = 55) for sample sizes from 20 to 2 L. The procedural blank ranges from 1.4 to 1.1 ng, for sample sizes ranging from 20 to 2 L, respectively, which, converted into Fe concentrations, corresponds to blank contributions of 0.001 and 0.010 nmol L(-1), respectively. Measurement precision determined from replicate measurements of seawater samples and standard solutions is 0.08 per thousand (delta(56)Fe, 2SD). The precision is sufficient to clearly detect and quantify isotopic variations in the oceans, which so far have been observed to span 2.5 per thousand and thus opens new perspectives to elucidate the oceanic iron cycle.

Lead (Pb) isotopic fingerprinting and its applications in lead pollution studies in China: a review

As the most widely scattered toxic metal in the world, the sources of lead (Pb) observed in contamination investigation are often difficult to identify. This review presents an overview of the principles, analysis, and applications of Pb isotopic fingerprinting in tracing the origins and transport pathways of Pb in the environment. It also summarizes the history and current status of lead pollution in China, and illustrates the power of Pb isotopic fingerprinting with examples of its recent applications in investigating the effectiveness of leaded gasoline phase-out on atmospheric lead pollution, and the sources of Pb found in various environmental media (plants, sediments, and aquatic organisms) in China. The limitations of Pb isotopic fingerprinting technique are discussed and a perspective on its development is also presented. Further methodological developments and more widespread instrument availability are expected to make isotopic fingerprinting one of the key tools in lead pollution investigation.

Mass spectrometry and natural variations of iron isotopes

Although the processes that govern iron isotope variations in nature are just beginning to be understood, multiple studies attest of the virtue of this system to solve important problems in geosciences and biology. In this article, we review recent advances in the geochemistry, cosmochemistry, and biochemistry of iron isotopes. In Section 2, we briefly address the question of the nucleosynthesis of Fe isotopes. In Section 3, we describe the different methods for purifying Fe and analyzing its isotopic composition. The methods of SIMS, RIMS, and TIMS are presented but more weight is given to measurements by MC-ICPMS. In Section 4, the isotope anomalies measured in extraterrestrial material are briefly discussed. In Section 5, we show how high temperature processes like evaporation, condensation, diffusion, reduction, and phase partitioning can affect Fe isotopic composition. In Section 6, the various low temperature processes causing Fe isotopic fractionation are presented. These involve aqueous and biologic systems.

Precise Zn Isotopic Ratio Measurements of Human Red Blood Cell and Hair Samples by Multiple Collector-ICP-Mass Spectrometry

Precise 66Zn/64Zn and 68Zn/64Zn isotopic ratios of biochemical samples have been measured using multiple collector-ICP-mass spectrometry (MC-ICPMS). In order to eliminate the mass spectrometric interferences on Zn isotopes (e.g., 64Ni+ and 136Ba2+), we chemically purified the analyte using an ion chromatographic technique. The resulting precisions of the 66Zn/64Zn and 68Zn/64Zn ratio measurements were 0.05/1000 and 0.10/1000 (2SD), respectively, which were enough to detect the isotopic variation of Zn in nature. Red blood cell (RBC) samples were collected from five volunteers (four males and one female), including a series of 12 RBC samples from one person through monthly-based sampling over a year. These were analyzed to test possible seasonal changes and variations in 66Zn/64Zn and 68Zn/64Zn ratios among the individuals. The 66Zn/64Zn and 68Zn/64Zn ratios for a series of 12 RBC samples collected over a year were 0.43/1000 and 0.83/1000 higher than the values of highly purified Zn metal (JMC Zn), and no seasonal change could be found. The 66Zn/64Zn and 68Zn/64Zn ratios for RBC samples collected from five volunteers did not vary significantly. In order to investigate Zn isotopic heterogeneity in a human body, Zn isotopic ratios of a hair sample collected from one of the volunteers was also analyzed. The 66Zn/64Zn and 68Zn/64Zn ratios for the hair sample were 0.59/1000 and 1.14/1000 lower than the mean value of RBC samples. This result demonstrates that detectable isotopic fractionation occurs in the human body. The data obtained here suggest that the isotopic ratios of trace metals could provide new information about transportation of metal elements in vivo.

Atomic-resolution dynamic force microscopy and spectroscopy of a single-walled carbon nanotube: characterization of interatomic van der Waals forces

We report atomic-resolution imaging and site-specific quantitative force measurements on a single-walled carbon nanotube by dynamic force microscopy and three-dimensional force field spectroscopy at low temperatures. The topography imaged in the attractive force regime reflects the trigonal arrangement of the hollow sites as maxima. Individual force curves were unambiguously assigned to carbon atoms and hollow sites, respectively. Site-specific quantitative evaluation revealed that the short-range interatomic van der Waals forces are responsible for the atomic-scale contrast.

Isotopic Analysis of Fe in Human Red Blood Cells by Multiple Collector-ICP-Mass Spectrometry

Precise 56Fe/54Fe and 57Fe/54Fe isotopic ratios on human red blood cell (RBC) samples have been measured using multiple collector-ICP-mass spectrometry (MC-ICPMS). The mass spectrometric interferences on Fe isotopes (e.g., 56ArO+ and 57ArOH+) were successfully minimized by a dry plasma condition achieved by a desolvating nebulizer sample-introduction technique. In order to eliminate possible variations in the measured isotopic ratios due to non-mass spectrometric interferences, Fe was separated from remaining organic compounds and major co-existing elements using an ion chromatographic technique. The resulting precisions of the 56Fe/54Fe and 57Fe/54Fe ratio measurements were 0.12 per thousand and 0.20 per thousand, respectively, which were high enough to detect the isotopic variation of Fe in nature. For an interlaboratory comparison, all of the Fe isotopic ratio data were normalized by the ratios for the IRMM-014 international isotopic standard. A series of 12 RBC samples were collected from one person through monthly-based sampling over a period of one year. These were analyzed to test possible seasonal changes in the 56Fe/54Fe and 57Fe/54Fe ratios. Moreover, in order to test possible variations in the 56Fe/54Fe and 57Fe/54Fe ratios among different people, RBC samples were collected from five volunteers (four males and one female). The 56Fe/54Fe and 57Fe/54Fe ratios for a series of 12 RBC samples collected over a one-year period show 3.06 per thousand and 4.51 per thousand lower than the values of IRMM-014, and no significant seasonal change could be found in the ratios. The lack in seasonal changes in the Fe isotopic ratios could be explained by a small contribution of the daily net-intake of Fe (1 - 2 mg/day) onto the total amount of Fe in the human body (2 - 4 g). The 56Fe/54Fe and 57Fe/54Fe ratios for RBC samples collected from four male samples did not vary measurably, whereas the Fe isotopic ratios for a female RBC were 0.3 per thousand/amu heavier than the mean value of four male samples. This difference in Fe isotopes among the individuals can be the result of a difference in uptake efficiency of the Fe through a dietary process from the digestive tract. The data obtained here demonstrate that the isotopic ratios of trace metals can provide new information about metabolic efficiencies of the metallic elements.

Absolute isotopic composition and atomic weight of commercial zinc using inductively coupled plasma mass spectrometry

Inductively coupled plasma mass spectrometry is introduced as a method for determining the absolute isotopic composition of zinc. The high ionization efficiency and time-independent characteristics of the mass spectrometry permit the absolute isotopic composition of high ionization potential elements. The mass discrimination of the instrument is calibrated by synthetic isotope mixtures prepared from highly enriched isotopes of zinc. The resulting isotope ratios yield atomic percents of 64Zn, 49.188 +/- 0.030; 66Zn, 27.792 +/- 0.041; 67Zn, 4.041 +/- 0.009; 68Zn, 18.378 +/- 0.050; and 70Zn, 0.600 +/- 0.003. This isotopic composition is different from those of conventional mass spectrometric measurements. Their differences depend on the mass differences about 0.8-1.2%/amu with enhancement of heavier isotopes. The atomic weight calculated from our isotopic composition is 65.3756 +/- 0.0040. The obtained atomic weight is fully consistent with that of a precise coulometric measurement in contrast to the previous mass spectrometric measurements. An isotopic variation of commercial zinc reagents has been investigated. A mass-dependent fractionation of 0.12%/amu is observed in a high-purity metal zinc, NIST-SRM 682, among five reagents. This mass dependence is probably inherited through their purification process.

Isotopic homogeneity of iron in the early solar nebula

The chemical and isotopic homogeneity of the early solar nebula, and the processes producing fractionation during its evolution, are central issues of cosmochemistry. Studies of the relative abundance variations of three or more isotopes of an element can in principle determine if the initial reservoir of material was a homogeneous mixture or if it contained several distinct sources of precursor material. For example, widespread anomalies observed in the oxygen isotopes of meteorites have been interpreted as resulting from the mixing of a solid phase that was enriched in 16O with a gas phase in which 16O was depleted, or as an isotopic 'memory' of Galactic evolution. In either case, these anomalies are regarded as strong evidence that the early solar nebula was not initially homogeneous. Here we present measurements of the relative abundances of three iron isotopes in meteoritic and terrestrial samples. We show that significant variations of iron isotopes exist in both terrestrial and extraterrestrial materials. But when plotted in a three-isotope diagram, all of the data for these Solar System materials fall on a single mass-fractionation line, showing that homogenization of iron isotopes occurred in the solar nebula before both planetesimal accretion and chondrule formation.