Carbonate uranium isotopes record global expansion of marine anoxia during the Toarcian Oceanic Anoxic Event.

The Toarcian Oceanic Anoxic Event (T-OAE; ~183 Mya) was a globally significant carbon-cycle perturbation linked to widespread deposition of organic-rich sediments, massive volcanic CO2 release, marine faunal extinction, sea-level rise, a crisis in carbonate production related to ocean acidification, and elevated seawater temperatures. Despite recognition of the T-OAE as a potential analog for future ocean deoxygenation, current knowledge on the severity of global ocean anoxia is limited largely to studies of the trace element and isotopic composition of black shales, which are commonly affected by local processes. Here, we present the first carbonate-based uranium isotope (δ238U) record of the T-OAE from open marine platform limestones of the southeastern Tethys Ocean as a proxy for global seawater redox conditions. A significant negative δ238U excursion (~0.4‰) is recorded just prior to the onset of the negative carbon isotope excursion comprised within the T-OAE, followed by a long-lived recovery of δ238U values, thus confirming that the T-OAE represents a global expansion of marine anoxia. Using a Bayesian inverse isotopic mass balance model, we estimate that anoxic waters covered ~6 to 8% of the global seafloor during the peak of the T-OAE, which represents 28 to 38 times the extent of anoxia in the modern ocean. These data, combined with δ238U-based estimates of seafloor anoxic area for other CO2-driven Phanerozoic OAEs, suggest a common response of ocean anoxia to carbon release, thus improving prediction of future anthropogenically induced ocean deoxygenation.

SciPhon: a data analysis software for nuclear resonant inelastic X-ray scattering with applications to Fe, Kr, Sn, Eu and Dy.

The synchrotron radiation technique of nuclear resonant inelastic X-ray scattering (NRIXS), also known as nuclear resonance vibrational spectroscopy or nuclear inelastic scattering, provides a wealth of information on the vibrational properties of solids. It has found applications in studies of lattice dynamics and elasticity, superconductivity, heme biochemistry, seismology, isotope geochemistry and many other fields. It involves probing the vibrational modes of solids by using the nuclear resonance of Mössbauer isotopes such as 57Fe, 83Kr, 119Sn, 151Eu and 161Dy. After data reduction, it provides the partial phonon density of states of the Mössbauer isotope that is investigated, as well as many other derived quantities such as the mean force constant of the chemical bonds and the Debye velocity. The data reduction is, however, not straightforward and involves removal of the elastic peak, normalization and Fourier-Log transformation. Furthermore, some of the quantities derived are highly sensitive to details in the baseline correction. A software package and several novel procedures to streamline and hopefully improve the reduction of the NRIXS data generated at sector 3ID of the Advanced Photon Source have been developed. The graphical user interface software is named SciPhon and runs as a Mathematica package. It is easily portable to other platforms and can be easily adapted for reducing data generated at other beamlines. Several tests and comparisons are presented that demonstrate the usefulness of this software, whose results have already been used in several publications. Here, the SciPhon software is used to reduce Kr, Sn, Eu and Dy NRIXS data, and potential implications for interpreting natural isotopic variations in those systems are discussed.

Ruthenium isotopes show the Chicxulub impactor was a carbonaceous-type asteroid.

An impact at Chicxulub, Mexico, occurred 66 million years ago, producing a global stratigraphic layer that marks the boundary between the Cretaceous and Paleogene eras. That layer contains elevated concentrations of platinum-group elements, including ruthenium. We measured ruthenium isotopes in samples taken from three Cretaceous-Paleogene boundary sites, five other impacts that occurred between 36 million to 470 million years ago, and ancient 3.5-billion- to 3.2-billion-year-old impact spherule layers. Our data indicate that the Chicxulub impactor was a carbonaceous-type asteroid, which had formed beyond the orbit of Jupiter. The five other impact structures have isotopic signatures that are more consistent with siliceous-type asteroids, which formed closer to the Sun. The ancient spherule layer samples are consistent with impacts of carbonaceous-type asteroids during Earth's final stages of accretion.

Copper isotope ratios in serum do not track cancerous tumor evolution, but organ failure.

Relative to healthy controls, lighter copper isotopic compositions have been observed in the serum of breast cancer and end-stage liver disease patients, raising the possibility that Cu isotope ratios could be used as a tracer for disease progression. Here, we assess the potential of natural Cu isotopic variations (expressed as δ65Cu) as diagnostic tools for cancer progression and/or liver failure by performing a first-order analysis of Cu isotopic cycling in the human body. Using a box model, we simulate the kinetics of Cu mass transfer throughout significant reservoirs in the body, allowing isotopic fractionation to occur during Cu uptake/release from these reservoirs. With this model, we determine under which conditions the serum δ65Cu values would reflect perturbation related to cancer growth and/or liver failure at a level resolvable with modern mass spectrometry. We find that tumor growth alone is unable to explain the light isotopic signature observed in serum. Instead, we find that metabolic changes to the liver function resulting in a ∼1‰ isotope fractionation during Cu uptake from the blood into the liver can readily explain the long-term serum isotopic shift of ∼0.2‰ observed in cancer patients. A similar fractionation (∼1.3‰) during Cu uptake into the liver also readily explains the -1.2‰ shift observed in the serum of cirrhosis patients with ascites, suggesting a potentially common driver of isotopic fractionation in both cases. Using this model, we then test hypotheses put forward by previous studies and begin to probe the mechanisms behind the measured isotopic compositions.

I/Pu reveals Earth mainly accreted from volatile-poor differentiated planetesimals.

The observation that mid-ocean ridge basalts had ~3× higher iodine/plutonium ratios (inferred from xenon isotopes) compared to ocean island basalts holds critical insights into Earth's accretion. Understanding whether this difference stems from core formation alone or heterogeneous accretion is, however, hindered by the unknown geochemical behavior of plutonium during core formation. Here, we use first-principles molecular dynamics to quantify the metal-silicate partition coefficients of iodine and plutonium during core formation and find that both iodine and plutonium partly partition into metal liquid. Using multistage core formation modeling, we show that core formation alone is unlikely to explain the iodine/plutonium difference between mantle reservoirs. Instead, our results reveal a heterogeneous accretion history, whereby predominant accretion of volatile-poor differentiated planetesimals was followed by a secondary phase of accretion of volatile-rich undifferentiated meteorites. This implies that Earth inherited part of its volatiles, including its water, from late accretion of chondrites, with a notable carbonaceous chondrite contribution.

Determination of Rare Earth Element Isotopic Compositions Using Sample-Standard Bracketing and Double-Spike Approaches.

Rare earth elements (REEs) have been found to have numerous uses to trace geological and cosmochemical processes through analyses of elemental patterns, radioactive decay, nucleosynthetic anomalies, and cosmogenic effects. Stable isotopic fractionation is one aspect of REE geochemistry that has been seldom studied, with most publications focusing on the development of analytical methodologies for individual REEs, and most applications concerning terrestrial igneous rocks. In this study, we present a method to systematically analyze stable isotopic fractionations of 8 REEs, including Ce, Nd, Sm, Eu, Gd, Dy, Er, and Yb, using sample-standard bracketing (SSB) and double-spike (DS) approaches. All REEs are separated and purified using a fluoropolymer pneumatic liquid chromatography (FPLC) system. We introduce procedures for identifying and correcting some isobaric interferences in double-spike data reduction. Several geostandards, including igneous rocks and sediments, are analyzed using SSB and DS methods. The results indicate that REE isotopic fractionation in igneous processes is limited, except for Eu. Other REEs can still be isotopically fractionated by low-temperature processes and kinetic effects at a high temperature.

Survival of presolar p-nuclide carriers in the nebula revealed by stepwise leaching of Allende refractory inclusions.

The 87Rb-87Sr radiochronometer provides key insights into the timing of volatile element depletion in planetary bodies, yet the unknown nucleosynthetic origin of Sr anomalies in Ca-Al-rich inclusions (CAIs, the oldest dated solar system solids) challenges the reliability of resulting chronological interpretations. To identify the nature of these Sr anomalies, we performed step-leaching experiments on nine unmelted CAIs from Allende. In six CAIs, the chemically resistant residues (0.06 to 9.7% total CAI Sr) show extreme positive µ84Sr (up to +80,655) and 87Sr variations that cannot be explained by decay of 87Rb. The extreme 84Sr but more subdued 87Sr anomalies are best explained by the presence of a presolar carrier enriched in the p-nuclide 84Sr. We argue that this unidentified carrier controls the isotopic anomalies in bulk CAIs and outer solar system materials, which reinstates the chronological significance of differences in initial 87Sr/86Sr between CAIs and volatile-depleted inner solar system materials.

Protein Phosphatase 2A as a Therapeutic Target in Small Cell Lung Cancer.

Protein phosphatase 2A (PP2A), a serine/threonine phosphatase involved in the regulation of apoptosis, proliferation, and DNA-damage response, is overexpressed in many cancers, including small cell lung cancer (SCLC). Here we report that LB100, a small molecule inhibitor of PP2A, when combined with platinum-based chemotherapy, synergistically elicited an antitumor response both in vitro and in vivo with no apparent toxicity. Using inductively coupled plasma mass spectrometry, we determined quantitatively that sensitization via LB100 was mediated by increased uptake of carboplatin in SCLC cells. Treatment with LB100 alone or in combination resulted in inhibition of cell viability in two-dimensional culture and three-dimensional spheroid models of SCLC, reduced glucose uptake, and attenuated mitochondrial and glycolytic ATP production. Combining LB100 with atezolizumab increased the capacity of T cells to infiltrate and kill tumor spheroids, and combining LB100 with carboplatin caused hyperphosphorylation of the DNA repair marker γH2AX and enhanced apoptosis while attenuating MET signaling and invasion through an endothelial cell monolayer. Taken together, these data highlight the translational potential of inhibiting PP2A with LB100 in combination with platinum-based chemotherapy and immunotherapy in SCLC.

Extreme Zr stable isotope fractionation during magmatic fractional crystallization.

Zirconium is a commonly used elemental tracer of silicate differentiation, yet its stable isotope systematics remain poorly known. Accessory phases rich in Zr4+ such as zircon and baddeleyite may preserve a unique record of Zr isotope behavior in magmatic environments, acting both as potential drivers of isotopic fractionation and recorders of melt compositional evolution. To test this potential, we measured the stable Zr isotope composition of 70 single zircon and baddeleyite crystals from a well-characterized gabbroic igneous cumulate. We show that (i) closed-system magmatic crystallization can fractionate Zr stable isotopes at the >0.5% level, and (ii) zircon and baddeleyite are isotopically heavy relative to the melt from which they crystallize, thus driving chemically differentiated liquids toward isotopically light compositions. Because these effects are contrary to first-order expectations based on mineral-melt bonding environment differences, Zr stable isotope fractionation during zircon crystallization may not solely be a result of closed-system thermodynamic equilibrium.

Origin of uranium isotope variations in early solar nebula condensates.

High-temperature condensates found in meteorites display uranium isotopic variations ((235)U/(238)U), which complicate dating the solar system's formation and whose origin remains mysterious. It is possible that these variations are due to the decay of the short-lived radionuclide (247)Cm (t 1/2 = 15.6 My) into (235)U, but they could also be due to uranium kinetic isotopic fractionation during condensation. We report uranium isotope measurements of meteoritic refractory inclusions that reveal excesses of (235)U reaching ~+6% relative to average solar system composition, which can only be due to the decay of (247)Cm. This allows us to constrain the (247)Cm/(235)U ratio at solar system formation to (1.1 ± 0.3) × 10(-4). This value provides new clues on the universality of the nucleosynthetic r-process of rapid neutron capture.