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Oxygen isotope compositions of fossil foraminifera tests are commonly used proxies for ocean paleotemperatures, with reconstructions spanning the last 112 million years. However, the isotopic composition of these calcitic tests can be substantially altered during diagenesis without discernible textural changes. Here, we investigate fluid-mediated isotopic exchange in pristine tests of three modern benthic foraminifera species ( Ammonia sp ., Haynesina germanica , and Amphistegina lessonii ) following immersion into an 18 O-enriched artificial seawater at 90 °C for hours to days. Reacted tests remain texturally pristine but their bulk oxygen isotope compositions reveal rapid and species-dependent isotopic exchange with the water. NanoSIMS imaging reveals the 3-dimensional intra-test distributions of 18 O-enrichment that correlates with test ultra-structure and associated organic matter. Image analysis is used to quantify species level differences in test ultrastructure, which explains the observed species-dependent rates of isotopic exchange. Consequently, even tests considered texturally pristine for paleo-climatic reconstruction purposes may have experienced substantial isotopic exchange; critical paleo-temperature record re-examination is warranted. Paleoclimate reconstructions commonly use oxygen isotope compositions from fossil foraminifera tests as proxies. Here, the authors show that these tests exchange O-isotopes with surrounding fluids, with implications for paleotemperature records.

In contrast to abiotically formed carbonates, biogenetic carbonates have been observed to be nanocomposite, organo-mineral structures, the basic build-blocks of which are particles of quasi-uniform size (10–100 nm) organized into complex higher-order hierarchical structures, typically with highly controlled crystal-axis alignments. Some of these characteristics serve as criteria for inferring a biological origin and the state of preservation of fossil carbonate materials, and to determine whether the biomineralization process was biologically induced or controlled. Here we show that a calcium storage structure formed by the American lobster, a gastrolith initially consisting of amorphous calcium carbonate (ACC) and amorphous calcium phosphate (ACP), post-mortem can crystallize into (thus secondary) calcite with structural properties strongly influenced by the inherited organic matrix. This secondary calcite meets many structural criteria for biominerals (thus called the biomorphic calcite), but differs in trace element distributions (e.g., P and Mg). Such observations refine the capability to determine whether a fossil carbonates can be attributed to biogenic processes, with implications for the record of life on Earth and other terrestrial planets.

Fossilized remains of marine calcifiers constitute the physical basis for reconstructions of both deep ocean and sea-surface temperatures going back millions of years, but paleoclimate records derived from their isotope and trace-element chemistry can be biased by diagenesis. Experiments simulating diagenesis in the presence of an 18 O-rich seawater analogue were conducted with modern and 14 Myr old foraminifera ( Ammonia sp.) tests to investigate their relative susceptibility to oxygen isotope exchange. The fossilized tests were of exceptional preservation and similar to modern tests in terms of structure and crystalline organization, but had experienced partial loss of embedded organic structures, thus a priori offering fewer preferential pathways for porewaters to penetrate the tests. NanoSIMS imaging revealed that oxygen isotope exchange was pervasive in fossil tests, with isotopic exchange occurring at approximately half the rate of modern tests. The results unequivocally show that fossil biocalcites are metastable and remain more susceptible to isotope exchange than abiotic calcites millions of years after sedimentation and burial.

The oxygen isotopic compositions of fossil foraminifera tests constitute a continuous proxy record of deep-ocean and sea-surface temperatures spanning the last 120 million years. Here, by incubating foraminifera tests in 18 O-enriched artificial seawater analogues, we demonstrate that the oxygen isotopic composition of optically translucent, i.e., glassy, fossil foraminifera calcite tests can be measurably altered at low temperatures through rapid oxygen grain-boundary diffusion without any visible ultrastructural changes. Oxygen grain boundary diffusion occurs sufficiently fast in foraminifera tests that, under normal upper oceanic sediment conditions, their grain boundaries will be in oxygen isotopic equilibrium with the surrounding pore fluids on a time scale of <100 years, resulting in a notable but correctable bias of the paleotemperature record. When applied to paleotemperatures from 38,400 foraminifera tests used in paleoclimate reconstructions, grain boundary diffusion can be shown to bias prior paleotemperature estimates by as much as +0.86 to −0.46 °C. The process is general and grain boundary diffusion corrections can be applied to other polycrystalline biocarbonates composed of small nanocrystallites (<100 nm), such as those produced by corals, brachiopods, belemnites, and molluscs, the fossils of which are all highly susceptible to the effects of grain boundary diffusion.

We investigated the external morphologies and internal compositional zoning patterns of clinopyroxene phenocrysts in an ankaramite of Haleakala volcano (Hawaii) to constrain magma crystallization conditions in the volcano’s postshield stage. The phenocrysts are characterized by euhedral faceted morphologies and crystallographically coherent subcrystals. Quantitative EPMA and X-ray element mapping reveal two domains within the crystals: porous, Si–Mg–Ca–Cr-rich zones associated with the forms {100}, {010} and {110}, and nonporous, Al–Ti–Na-rich zones associated with the forms {−111}. The chemical variations, internal porosity and parallel subcrystals are consistent with nonconcentric crystal growth at varying degrees of supersaturation. We infer that initial growth occurred in a diffusion-limited regime to produce dendritic crystals; subsequent growth was markedly slower, with lesser supersaturation allowing dendrites to infill and produce polyhedral external morphologies. This sequence promoted the evolution of crystals from an hourglass shape with dominant {−111} forms, to sector-zoned euhedral crystals in which elements were partitioned according to: (Al + Ti + Na) {−111}  = (Si + Mg + Cr + Ca) {110},{100},{010} . Infilling of dendritic crystals occurred to a greater extent on faster-growing sectors and was interrupted by the eruption, resulting in porosity of the slower-growing {hk0} sectors. Outermost Na-poor rims formed on all sectors due to slower growth rate under interface-limited conditions. Paradoxically, high levels of supersaturation producing large crystals of clinopyroxene (and olivine) are indicated in the volcano’s deep-seated reservoir and lower degrees of supersaturation characterize syn-eruptive crystal growth. The presence of vapor bubbles within the melt-filled crystal embayments and inclusions suggests rapid clinopyroxene growth caused volatile saturation and reservoir pressurization, leading to eruption of the ankaramite.

The physical properties of the hydrous phyllosilicate lizardite have been investigated by atomistic simulation using the GULP code based on transferable semi-empirical interatomic potentials. Lizardite behavior was first investigated during structure relaxation at room temperature. The Helmholtz free energy is minimum for an equilibrium structure that is in agreement with experiment. The bulk, shear, and Young modulii for lizardite were calculated along with the Poisson ratio. From the shear and bulk modulii, we also calculated translational and longitudinal acoustic wave velocities that are important quantities for tectonophysics models. As expected, lizardite is stiffer in the a direction parallel to the layers than in the c perpendicular direction; the variation of the unit cell parameters with pressure is in good agreement with experiment. The cohesive energy between two successive layers along c direction was calculated at 0.33 eV (i.e., 0.11 eV per OH bond) in good agreement with recent ab initio calculations. Upon pressure and temperature variations, we evidenced that structural changes are mainly pressure induced; pressure being accommodated by a decrease of the c parameter up to 10 GPa. We also found that the change of slope in the derivative of the c cell parameter with respect to pressure occurring around 2 GPa originates from the bending of the interlayer hydroxyl groups with respect to the layer normal direction.

ObjectivesThe relationship between stroke topography (ie, the regions damaged by the infarct) and functional outcome can aid clinicians in their decision-making at the acute and later stages. However, the side (left or right) of the stroke may also influence the identification of clinically relevant regions. We sought to determine which brain regions are associated with good functional outcome at 3 months in patients with left-sided and right-sided stroke treated by endovascular treatment using the diffusion-weighted imaging-Alberta Stroke Program Early CT Score (DWI-ASPECTS).MethodsPatients with ischaemic stroke (n = 405) were included from the ASTER trial and Pitié-Salpêtrière registry. Blinded readers rated ASPECTS on day 1 DWI. Stepwise logistic regression analyses were performed to identify the regions related to 3-month outcome in left (n = 190) and right (n = 215) sided strokes with the modified Rankin scale (0–2) as a binary independent variable and with the 10 regions-of-interest of the DWI-ASPECTS as independent variables.ResultsMedian National Institute of Health Stroke Scale (NIHSS) at baseline was 17 (IQR: 12–20), median age was 70 years (IQR: 58–80) and median day-one NIHSS 9 (IQR: 4–18). Not all brain regions have the same weight in predicting good outcome at 3 months; moreover, these regions depend on the affected hemisphere. In left-sided strokes, the multivariate analysis revealed that preservation of the caudate nucleus, the internal capsule and the cortical M5 region were independent predictors of good outcome. In right-sided strokes, the cortical M3 and M6 regions were found to be clinically relevant.ConclusionCortical non-motors areas related to outcome differed between left-sided and right-sided strokes. This difference might reflect the specialisation of the dominant and non-dominant hemispheres for language and attention, respectively. These results may influence decision-making at the acute and later stages.Trial registration number NCT02523261.

Background and purpose Patients with acute ischaemic stroke and a large vessel occlusion who present to a non‐endovascular‐capable centre often require inter‐hospital transfer for thrombectomy. Whether the inter‐hospital transfer time is associated with 3‐month functional outcome is poorly known. Methods Acute stroke patients enrolled between January 2015 and December 2022 in the prospective French multicentre Endovascular Treatment of Ischaemic Stroke registry were retrospectively analysed. Patients with an anterior circulation large vessel occlusion transferred from a non‐endovascular to a comprehensive stroke centre for thrombectomy were eligible. Inter‐hospital transfer time was defined as the time between imaging in the referring hospital and groin puncture for thrombectomy. The relationship between transfer time and favourable 3‐month functional outcome (modified Rankin Scale 0–2) was assessed through a mixed logistic regression model adjusting for centre and symptom‐onset‐to‐referring‐hospital imaging time, age, sex, diabetes, referring hospital National Institutes of Health Stroke Scale score, Alberta Stroke Programme Early Computed Tomography Score, occlusion site and intravenous thrombolysis use. Results Overall, 3769 patients were included (median inter‐hospital transfer time 161 min, interquartile range 128–195; 46% with favourable outcome). A longer transfer time was independently associated with lower rates of favourable outcome (p < 0.001). Compared to patients with transfer time below 120 min, there was a 15% reduction in the odds of achieving favourable outcome for transfer times between 120 and 180 min (adjusted odds ratio 0.85; 95% confidence interval 0.67–1.07), and a 36% reduction for transfer times beyond 180 min (adjusted odds ratio 0.64; 95% confidence interval 0.50–0.81). Conclusions A shorter inter‐hospital transfer time is strongly associated with favourable 3‐month functional outcome. A speedier inter‐hospital transfer is of critical importance to improve outcome.