The compositions of planetary atmospheres provide key constraints on the origin and evolution of the planets. Mars has a thin atmosphere dominated by CO₂, with Ne detected by the Viking mission, although its abundance and isotopic composition is not well defined. A major technical challenge for in situ Ne measurements on Mars is to separate Ne from Ar before mass spectrometry, because ⁴⁰Ar²⁺ interferes with ²⁰Ne⁺. Previous studies have demonstrated that Ne–Ar separation can be achieved using polyimide membranes. In order to characterize the temperature dependence of permeation relevant to Martian mission, we investigated gas permeation through a 100-μm-thick polyimide sheet at 6°C, –18°C, and –38°C, and measured the permeated He, Ne, and Ar amounts, as well as ²⁰Ne/²²Ne ratio. The amounts of permeated He and Ne decrease with decreasing temperature. At –38°C, the permeated ⁴He and ²⁰Ne amounts are lower than the room temperature values by factors of ~6 and ~7, respectively. No permeated ⁴⁰Ar above background level was detected. The ²⁰Ne/²²Ne ratios corrected for mass-dependent fractionation agree with the terrestrial atmospheric ratio within analytical uncertainty, except during initial non-steady-state permeation at –38°C. Temperature dependency of permeated amounts indicates that the permeation fluxes through a 100-μm-thick polyimide at 20°C give 2.2 × 10^–11 and 2.7 × 10^–12 cm³STP/sec/cm²/Pa for ⁴He and ²⁰Ne, respectively. Under Martian atmospheric pressure, permeation through a 100-μm-thick polyimide for 40–60 min at temperature between ~10°C and room temperature provides a Ne amount of 1–2 × 10^–9 cm³STP/100 cm² with effective Ne-Ar separation.

The rare earth element (REE) europium (Eu) exists in Eu²⁺ and Eu³⁺ states. The Eu²⁺ can be substituted for Ca²⁺ during plagioclase feldspar crystallization in reducing magmas to create an observable Eu anomaly in REE distribution patterns. Europium has two stable isotopes, ¹⁵¹Eu and ¹⁵³Eu. Recent reports for Eu isotope ratios in igneous rocks indicate that Eu anomalies and isotope fractionation show good correlation, suggesting that Eu isotope fractionation appears due to feldspar crystallization during magma differentiation. Here, we report Eu isotope ratio and REE concentrations for five feldspar standard reference materials (SRMs) such as JF-1, JF-2, SRM 70a, SRM 70b, and SRM 99a prepared by the Geological Survey of Japan (GSJ) and National Institute of Standards and Technology (NIST) of USA. This study is the first investigation of the Eu isotope variation in feldspars to test several hypotheses for the origin of Eu isotope fractionation in igneous rocks. The chemical compositions of four feldspar SRMs except SRM 99a indicate that they are close to the KAlSi₃O₈ end-member within the feldspar series.

The SRM 99a meanwhile indicated oligoclase composition. Most feldspar SRMs showed chondrite-normalized patterns of light REE (LREE)-enrichment and heavy REE (HREE)-depletion or flat REE patterns with large positive Eu anomalies. This did not hold true for NIST SRM 70b, which contains small amounts of impurities. Results showed that potassium feldspar SRMs were enriched in the lighter Eu isotope (i.e., had negative δ¹⁵³Eu values), whereas the sodium feldspar SRM (NIST SRM 99a) was enriched in the heavier Eu isotope (i.e., had positive δ¹⁵³Eu values). Interpretation of Eu isotope ratios in igneous rocks should thus consider feldspar crystallization during magma differentiation.

Carbonaceous chondrites contain organic matter, but the majority consists of complex macromolecular organic matter collected after acid demineralization. The N contents in carbonaceous chondrites are much lower than C, limiting our understanding of N-bearing functional groups. However, such N-containing compounds could be precursors for life’s raw materials, making detailed chemical analysis essential. This study investigates N-containing organic matter such as N-heterocycles and amines, in various carbonaceous chondrites and xenolithic C-rich clasts using high-sensitivity N K-edge X-ray absorption near-edge structure (XANES) spectroscopy at SPring-8. We compared intact chondrites and insoluble organic matter (IOM) from Orgueil, Murchison, and Tagish Lake meteorites. Most chondrites exhibit three distinct N-XANES peaks: (A) pyridinic N (398.7 eV), (B) pyridinic N and/or nitriles (399.7 eV), and (C) pyrrolic N, amines, amides, and/or ammonium salts (400.8 eV). The Zag meteorite clast and ungrouped type 2 chondrites, such as Tagish Lake and Tarda, show an intense peak at 400.8 eV, indicating enrichment in non-conjugated N-compounds such as amines, amides, and/or ammonium salts. This suggests that their parent bodies contained more abundant ammonia and water. Comparing intact chondrites and IOM reveals significant differences in N-XANES features, suggesting acid-labile N-bearing moieties, like amides and ammonium salts, in addition to solvent extractable compounds such as amines and amino acids, are lost or altered during IOM extraction. This implies that extraterrestrial N compounds may be more diverse and abundant than previously recognized. These findings provide new insights into the N chemistry of meteorites and their potential contribution to the prebiotic inventory of early Earth.

This paper provides the first wide-ranging data for iodine concentrations of natural CaCO₃ samples (50 in total) from various geologic and marine-biogenic sources. The geologic samples are (i) calcite and aragonite crystals grown in underground or cave environments and (ii) calcite-aragonite coexisting travertines deposited from mountain spring water. The marine-biogenic samples are shells/skeletons/spicules of bivalves, gastropods, anthozoans, hydrozoans, bryozoans and foraminifera (36 extant and 3 extinct species), each consisting of either calcite, aragonite, or both, and including two geochemical reference materials GSJ CRM JCt-1 (giant clam) and JCp-1 (scleractinian coral). The iodine concentration data show distinct differences depending on the sample source and taxonomic group, probably indicating effects of (i) environmental conditions (e.g., redox conditions) and (ii) inter-taxonomic differences in the iodine-incorporation mechanism. Some samples with lowest iodine concentrations suggest that iodine (probably iodate) is incorporated more preferentially into calcite than into aragonite, as previously demonstrated in a laboratory experiment and a crystal-structure simulation. Measurements of Ca, Mg, Sr and Na were also made for all the samples, which revealed that some calcite samples (e.g., bryozoan skeletons) were composed of magnesian calcite with Mg and Ca concentrations of ~12,000–42,000 ppm and ~370,000–340,000 ppm, respectively (i.e., the higher the Mg concentration, the lower the Ca concentration). For more accurate expression of the iodine concentration in various natural CaCO₃ samples, including magnesian calcite, we propose the I/(Ca + Mg + Sr + Na) ratio instead of the I/Ca and I/(Ca + Mg) ratios; in future studies, it may be desirable to investigate, for some specific marine CaCO₃ materials, whether the I/(Ca + Mg + Sr + Na) ratio can practically be a more accurate paleo-redox proxy in comparison with the I/Ca and I/(Ca + Mg) ratios. Our dataset and detailed discussion will make a significant contribution to iodine-based geochemistry and marine biology.

Soluble organic matter (SOM) in carbonaceous chondrites is an important aspect of understanding the origin and evolution of extraterrestrial organic matter. Interactions with minerals and water on planetesimals are essential for the formation and evolution of SOM, yet the detailed processes remain poorly understood. To elucidate these processes, it is necessary to establish relationships between SOM and minerals, particularly secondary minerals.

In this study, nitrogen (N)-heterocyclic compounds (CHN compounds) in the methanol extracts of powdered Murchison meteorite fragments were characterized by high-performance liquid chromatography coupled with high-resolution mass spectrometry (HPLC/HRMS). Their abundance patterns and chemical characteristics were examined in direct relation to mineral compositions determined by X-ray diffraction (XRD) from the same samples.

Five homologous series of CHN compounds (alkylpyridines: C_nH_2n–4N⁺ or C_nH_2n–6N⁺, alkylpiperidines: C_nH_2n+2N⁺, and alkylimidazoles: C_nH_2n–1N₂⁺ or C_nH_2n–3N₂⁺, which were identified as positive ions) were identified from all of the samples. XRD analyses revealed inter-sample variability in the abundance of phyllosilicate, anhydrous silicates, sulfides, and carbonates. Several CHN homologous series exhibited systematic relationships with alteration minerals, particularly phyllosilicates and magnetite, whereas correlations with minor phases were generally weak. These relationships are consistent with water–mineral–organic interactions on the Murchison parent body, such as mineral-surface/interlayer interactions, fluid-driven chromatographic effects during aqueous alteration, redox-dependent alteration, and the potential heterogeneity of precursor organic molecules. Although this present approach is not universally applicable to all classes of SOM and requires careful evaluation of potential mineral alteration during extraction, it enables direct comparisons between SOM and minerals, thereby providing new insights into water–mineral–organic interactions on planetesimals.

Volcanic eruptions that formed Ontong Java Nui (OJN) during the Aptian (~120 Ma), Early Cretaceous, triggered substantial environmental perturbations, including global warming and Oceanic Anoxic Event (OAEs) 1a. However, the precise transition of OJN eruption styles and the influence of each volcanic phase on Earth’s environment remains poorly understood. Here, we present Pb isotopic evidence for the OJN as the source of tuffaceous sedimentary sequence deposited on nearby Magellan Rise. Furthermore, we reviewed geochemical and lithological data around OAE1a, and updated the discussion on how the OJN emplacement influenced the earth environment. Our results point to explosive OJN eruption during the earliest phase of OAE1a based on compiled geochemical and lithological data. Stratigraphic variations in Pb isotopic compositions during this volcanic phase indicate a transition in OJN volcanism, from Kwaimbaita/Kroenke-like magma eruptions that formed the lower part of OJN to Singgalo-like magma eruptions that formed the upper part. Based on previously reported isotopic (Os and C), mineralogical, and geochemical data, this short (~250 kyr) explosive volcanic phase, indicated by the Pb isotopic signal, was accompanied by extensive volatile emissions and corresponds to the onset of the previously documented early to mid-Aptian environmental perturbations (global warming, OAE1a, and the nannoconid crisis).

Air-sea mercury (Hg) exchange is an important process in the natural Hg cycle. Hg evasion from oceans accounts for approximately 40% of the global Hg emissions into the atmosphere, which was estimated to be 8,000 t yr^–1. In this study, we determined Hg fluxes through dissolved gaseous Hg (DGM) measurements using a manual method along a 47°N transect of the North Pacific Ocean and Alaska Bay in the summer of 2017, and conducted continuous monitoring using a gas-liquid equilibrator system in sea areas between 30°N and 50°N in the western North Pacific Ocean during the summer of 2022 and 2023. Atmospheric gaseous elemental Hg (GEM) was also continuously observed. The average GEM concentrations in 2017 and 2023 were 1.54 ± 0.22 and 1.25 ± 0.27 ng m^–3, respectively, similar to the background levels of the Northern Hemisphere. In contrast, GEM concentrations in 2022 reached approximately 2.00 ng m^–3. The GEM and DGM concentrations and Hg fluxes gradually increased from north to south. The Hg fluxes were nearly zero in the region around 45°N. Hg evasion fluxes were greater between 30–35°N because of higher DGM concentrations. In addition, atmospheric GEM and seawater DGM concentrations were positively correlated with surface seawater temperature (SST). From these results, the boundary line of the SST between Hg evasion and invasion in the study areas was estimated at approximately 5°C, using a 1.50-ng m^–3 GEM background concentration for the Northern Hemisphere.