Global trends in novel stable isotopes in basalts: theory and observations

The geochemistry of global mantle melts suggests that both mid-ocean ridge basalts (MORB) and ocean island basalts (OIB) sample lithological and temperature heterogeneities originating in both the upper and lower mantle. Recently, non-traditional stable isotopes have been suggested as a new tool to complement existing tracers of mantle heterogeneity (e.g., major and trace elements, radiogenic isotopes), because mineral- and redox-specific equilibrium stable isotope fractionation effects can link the stable isotope ratios of melts to their source mineralogy and melting degree. Here, we investigate five stable isotope systems (Mg-Ca-Fe-V-Cr) that have shown promise in models or natural samples as tracers of mantle temperature and/or lithological heterogeneity. We use a quantitative model, combining thermodynamically self-consistent mantle melting and equilibrium isotope fractionation models, to explore the behaviour of the isotope ratios of these elements during melting of three mantle lithologies (peridotite, and silica-excess and silica-deficient pyroxenites), responding to changes in mantle mineralogy, oxygen fugacity, temperature and pressure.We find that, given current analytical precision, the stable isotope systems examined here are not predicted to be sensitive to mantle potential temperature variations through equilibrium isotope fractionation processes. By contrast, source lithological heterogeneity is predicted to be detectable in some cases in the stable isotope ratios of erupted basalts, although generally only at proportions of > 10% MORB-like pyroxenite in the mantle source, given current analytical precision. Magnesium and Ca stable isotopes show most sensitivity to a garnet-bearing source lithology, and Fe and Cr stable isotopes are potentially sensitive to the presence of MORB-like pyroxenite in the mantle source, although the behaviour of Cr isotopes is comparatively under-constrained and requires further work to be applied with confidence to mantle melts. When comparing the magnitude and direction of predicted equilibrium isotopic fractionation of peridotite and pyroxenite melts to natural MORB and OIB data, we find that aspects of the natural data (including the mean Mg-Ca-Fe-V isotopic composition of MORB, the range of Mg-Ca isotopic compositions seen in MORB data, the mean Mg-Ca-Cr isotopic composition of OIB, and the range of Mg-V-Cr isotopic compositions in OIB data) can be matched by equilibrium isotope fractionation during partial melting of peridotite and pyroxenite sources -- with pyroxenite required even for some MORB data. However, even when considering analytical uncertainty on natural sample measurements, the range in stable isotope compositions seen across the global MORB and OIB datasets suggests that kinetic isotope fractionation, or processes modifying the isotopic composition of recycled crustal material such that it is distinct from MORB, may be required to explain all the natural data. We conclude that the five stable isotope systems considered here have potential to be powerful complementary tracers to other geochemical tracers of the source lithology of erupted basalts. However, continued improvements in analytical precision in conjunction with experimental and theoretical predictions of isotopic fractionation between mantle minerals and melts are required before these novel stable isotopes can be unambiguously used to understand source heterogeneity in erupted basalts.

Algorithms and the Critical Theory of Technology

This chapter argues that the radical critique of computation and calculation must work from the register of capital. Using the example of the automation of control rights, it links 'algorithmic regulation' with mature capitalist logics — where capital dominates the labour–capital antagonism — to show why computation is necessarily a venue for radical political advocacy, an urgent task on the 'hard road to renewal'. The chapter treats 'data politics', or more precisely digitalization as a signature element within late neoliberalism. It uses two case studies involving property rights and differential class power to suggest that there are many good reasons to foreground Marxian-inspired contributions. The chapter attempts to specify a venue and criteria for politically meaningful scholarship. The issue is more than just analytical precision. At stake is the continuing relevance of a critical theory of technology that is politically adequate to understand the latest manoeuvre in the always-ready impulse of value towards the realization of its own totality.

Potassium isotopic heterogeneity in subducting oceanic plates

Oceanic crust and sediments are the primary K sinks for seawater, and they deliver considerable amounts of K to the mantle via subduction. Historically, these crustal components were not studied for K isotopes because of the lack of analytical precision to differentiate terrestrial variations. Here, we report a high-precision dataset that reveals substantial variability in oceanic plates and provides further insights into the oceanic K cycle. Sixty-nine sediments worldwide yield a broad δ41K range from −1.3 to −0.02‰. The unusually low values are indicative of release of heavy K during continental weathering and uptake of light K during submarine diagenetic alteration. Twenty samples of altered western Pacific crust from ODP Site 801 display δ41K from −0.60 to −0.05‰, averaging at −0.32‰. Our results indicate that submarine alteration of oceanic plates is essential for generating the high-δ41K signature of seawater. These regionally varying subducting components are heterogeneous K inputs to the mantle.

Comparative Study of Various Methods for Trace SF6 Measurement Using GC-µECD: Demonstration of Lab-Pressure-Based Drift Correction by Preconcentrator

This study presents a high-precision method, using a preconcentrator–gas chromatograph with microelectron capture detector (GC-μECD), to measure SF6 at ambient levels. Carboxen 1000 was used as an adsorbent for the preconcentrator and exhibited a high adsorption efficiency for N2O and SF6 and low adsorption efficiency for O2. This enabled the selective removal of atmospheric O2 from analytes and improved repeatability of the SF6 peak that followed the O2 peak, in a separation column of activated alumina F1. In addition, the increased sensitivity resulting from preconcentrated SF6 improved the signal-to-noise ratio. This led to better analytical precision in comparison with other measurement methods including the conventional and forecut–backflush (FCBF) methods. The precision-to-drift ratios of the conventional, FCBF, and preconcentration methods were 0.11, 0.10, and 0.03, respectively. Analytical precision of the preconcentration method was 0.08% for 10 consecutive injections; this was the best among the three methods. The long-term drift of the SF6 response was inversely proportional to the laboratory pressure. Based on this finding, room pressure can be used to correct for ECD signal drift, with an uncertainty of 0.14% over a 48-h period, using the preconcentration method. Another advantage of the preconcentration method was the excellent linearity of the SF6 response to a wide range of concentrations, including its ambient concentration.

Miniature radiocarbon measurements ( < 150 µg C) from sediments of Lake Żabińskie, Poland: effect of precision and dating density on age–depth models

The recent development of the MIni CArbon DAting System (MICADAS) allows researchers to obtain radiocarbon (14C) ages from a variety of samples with miniature amounts of carbon (<150 µg C) by using a gas ion source input that bypasses the graphitization step used for conventional 14C dating with accelerator mass spectrometry (AMS). The ability to measure smaller samples, at reduced cost compared with graphitized samples, allows for greater dating density of sediments with low macrofossil concentrations. In this study, we use a section of varved sediments from Lake Żabińskie, NE Poland, as a case study to assess the usefulness of miniature samples from terrestrial plant macrofossils for dating lake sediments. Radiocarbon samples analyzed using gas-source techniques were measured from the same depths as larger graphitized samples to compare the reliability and precision of the two techniques directly. We find that the analytical precision of gas-source measurements decreases as sample mass decreases but is comparable with graphitized samples of a similar size (approximately 150 µg C). For samples larger than 40 µg C and younger than 6000 BP, the uncalibrated 1σ age uncertainty is consistently less than 150 years (±0.010 F14C). The reliability of 14C ages from both techniques is assessed via comparison with a best-age estimate for the sediment sequence, which is the result of an OxCal V sequence that integrates varve counts with 14C ages. No bias is evident in the ages produced by either gas-source input or graphitization. None of the 14C ages in our dataset are clear outliers; the 95 % confidence intervals of all 48 calibrated 14C ages overlap with the median best-age estimate. The effects of sample mass (which defines the expected analytical age uncertainty) and dating density on age–depth models are evaluated via simulated sets of 14C ages that are used as inputs for OxCal P-sequence age–depth models. Nine different sampling scenarios were simulated in which the mass of 14C samples and the number of samples were manipulated. The simulated age–depth models suggest that the lower analytical precision associated with miniature samples can be compensated for by increased dating density. The data presented in this paper can improve sampling strategies and can inform expectations of age uncertainty from miniature radiocarbon samples as well as age–depth model outcomes for lacustrine sediments.

Addendum

There is currently a growing movement among some Christian philosophers to defend Reformed/Calvinist theological commitments with analytical precision and rigor. A number of the characteristic commitments of Reformed theology bear importantly on the problem of hell; the most important of these is theological determinism, which, when combined with a rejection of universalism, raises a host of serious problems. In addition to exacerbating concerns about divine justice and love, there are at least two doxastic problems that are unique to Calvinism. First is the problem of faith: a necessary condition of faith is trust, but a thorough understanding of the implications of Calvinist theology would seem to undermine one’s grounds for reasonably trusting God. Second is the problem of hope: Calvinism is incompatible with at least one of the deepest hopes of the Christian faith, while encouraging another hope that is thoroughly unedifying, and perhaps even despairing.

The United Nations

This chapter makes the case for greater analytical precision and historical reflection about the balance between change and continuity within the United Nations since its founding in 1945. The most pertinent changes fall under four headings: the emergence of new threats and new technological opportunities; the increasing role of non-state actors; the reformulation of state sovereignty; and the emergence of a multipolar world. This chapter examines the nature and role of each of these in today’s international system and urges readers to keep in mind three distinct analytical problems: defining the nature of change; determining the meaning of success and failure; and tracking the ups-and-downs in world politics. It also introduces the forty-four chapters that follow in The Oxford Handbook on the United Nations.

Validating critical analytical variables of a multiplexed gene expression assay measuring tumor inflammation designed to predict response to anti-PD1 therapy.

203 Background: The development and analytical performance of the Tumor Inflammation Signature (TIS) assay has been described previously. The TIS is an investigational use RNA expression assay on the nCounter Dx Analysis System, which is being evaluated as a patient enrichment biomarker for treatment with pembrolizumab single agent across multiple solid tumor types. Here we describe the analytical validation of the RNA input range and analytical precision starting from RNA isolated from formalin fixed paraffin embedded (FFPE) tissue blocks. Methods: Analytical validation of TIS assay performance across an RNA input range was performed using samples from 11 tumor types. The analytical precision between sites, instruments, reagent lots, and users was measured, using RNA samples isolated from FFPE tissue blocks. Results: The assay was validated across the specified RNA input range with ≥ 94% concordance at the minimum specified RNA input (50ng). The total standard deviation of the TIS score was < 0.04 units across three sites with ≥98% concordance between sites. The 6 users across the three sites did not significantly contribute to the assay variability. There was 100% concordance in biomarker high/low categorization between multiple reagent lots and multiple instruments. Conclusions: The analytical performance of the NanoString TIS assay has been validated to give consistent results across the RNA input range and between site, instrument, assay user, and reagent kit lot. The assay is well suited for decentralized clinical testing and is currently under investigation as a biomarker to enrich for response to anti-PD1 therapy across multiple tumor types.