A 1D model of the CS₂ reaction network with the addition of the photo-oxidation pathway has been developed and quantitatively studied. The reaction pathway analysis focusing on the sulfur element was applied to determine the importance of the photo-oxidation pathway in the atmospheric CS₂ sink resulting in a 15.8% of sulfur in the CS₂ reaction network passes through the photo-oxidation pathway under a global average solar radiation conditions and ranging from 8.1% to 18% depending on the irradiance intensity. The concentration of COS and SO₂, the main products of CS₂ atmospheric oxidation, changed slightly from the sulfur cycle developed with the updated CS₂ reaction network. 7.4% of the COS comes from the new pathway and a total of 40.9% of COS comes from the conversion of CS₂. A sulfur budget for the main species in the sulfur cycle was constructed, and the CS₂ lifetime was estimated to be 2–3 days. The newly added photo-oxidation pathway plays an moderate role in the CS₂ reaction network and has a high variability under specific geochemical conditions. The results of this report should be taken as an incentive for 3D climate-chemistry models to account for local COS sources.

The Matsushiro earthquake swarm, which unusually persisted from 1965 to 1967, generated a gush of groundwater at the end of the period so massive that it was referred to as a “water eruption”. In this study, we analyze the geochemistry of Matsushiro spring waters collected in 2009 and 2010, with a focus on Li and Sr isotopic ratios. The Li and Sr isotopic ratios of Matsushiro spring waters, excluding the samples most contaminated by surface-water influence, were +4.0‰ to +6.0‰ for δ⁷Li and 0.7044–0.7045 for ⁸⁷Sr/⁸⁶Sr. These isotopic ratios are similar to those of Matsushiro igneous rocks (δ⁷Li –1.2‰ to 5.4‰, ⁸⁷Sr/⁸⁶Sr 0.7043–0.7050), supporting the hypothesis that the Matsushiro deep-derived fluid has a magmatic origin. Based on our results, the δ⁷Li value of Matsushiro deep-derived fluid without contamination by surface water is estimated to be +4.2‰. Using a Li isotope geothermometer, we estimate that the fluid–rock reaction temperature between the Matsushiro deep-derived fluid and magma exceeded 700°C. Furthermore, the insights obtained from this study on Matsushiro spring waters, emphasizing the characteristics of magma-derived fluid in central Japan, provide valuable information for distinguishing the origin of previously ambiguous fluid associated with the earthquake swarm at the southeastern foot of Ontake volcano, central Japan.

Back-arc basins (BABs) form an integral but often neglected part in the framework of subduction zone system. Many studies on the BAB have focused on BAB basalts because they are more accessible than to the lower crust and underlying mantle. The Shikoku and Parece Vela Basins formed behind arc systems in the Philippine Sea host numerous oceanic core complexes (OCCs), dome-like bathymetric highs composed of lower crust and mantle materials. One of these OCCs named Mado Megamullion is the study target emplaced in the Shikoku Basin, where dolerite dike intrusions are recognized as a late back-arc magma activity. Ilmenite U–Pb dating of a dolerite sample revealed that the dolerite formed at 9.7 ± 6.3 Ma (2 sigma error, n = 24), at which the Shikoku Basin ceased spreading. Geochemical tracers of Ba/Yb, Ba/Nb, and Th/Nb were used to evaluate the extent of subduction input to dolerite-forming magmas. The results demonstrated that the subduction components did not reach the back-arc spreading center and hence the dolerite-forming magma was dry as the back-arc spreading center was well apart from the fluid-supplying slab when the Mado Megamullion was formed. The Mado Megamullion has ample potential to decode mature back-arc spreading system, whereas the OCCs located in initial spreading modes of the Shikoku Basin can decipher immature back-arc spreading system. Accurate understanding of BAB evolution will come from further investigations of time-dependent emplacements of OCCs in the Shikoku and Parece Vela BABs.

Brownish zones enriched in iron (oxyhydr)oxides often occur around fractures during granite weathering. The elemental distribution, color, iron oxide concentration, mineral assemblage, porosity, and iron diffusivity in the brownish zone around a fracture in the Hiroshima granite were investigated. From the fracture to the interior of the rock matrix, the iron concentration first increased with distance from the fracture, reaching a maximum at 4–10 mm, decreasing at 10–21 mm, and remaining constant in the whitish areas at greater distances. Iron oxides, thought to be mainly goethite and ferrihydrite, were distributed at the grain boundaries and concentrated in the altered portions of plagioclase. The selective iron dissolution method revealed that 0.32 wt% Fe is present as iron oxides in the brown zone. Numerical calculations of the reaction and transport of Fe near the fracture showed the following: under conditions where Fe does not precipitate, the dissolution of biotite takes less time to supply Fe for the formation of iron oxides than the diffusion of Fe from groundwater in the fracture; under conditions where Fe precipitates, the Fe that diffuses from the fracture almost completely precipitates in the vicinity of the fracture and is unlikely to be a major source of iron oxide in the brown zone. A large proportion of the brown zone Fe appears to have been derived from the dissolution of nearby biotite.

Proteins are composed of 20 different amino acids and are essential catalysts of many biological reactions for all extant life. Thus, understanding the origin of proteins is essential to understanding the origin of life. Glycine (Gly) is regarded as a reactive amino acid in peptide synthesis and is also important as the most abundant α-amino acid on the prebiotic Earth. Many investigations on peptide formation have revealed the importance of evaporative environments, reporting the formation of oligopeptides composed of both single amino acids (homo-oligopeptides) and multiple-type amino acids (hetero-oligopeptides). However, the extent of incorporation of amino acids of different reactivities in peptides is unclear. We performed long-period amino acid oligomerization experiments, simulating prebiotic alkaline evaporative environments. Alkaline aqueous solutions containing a 9:5 molar ratio (pH 9.1) or 1:1 molar ratio (pH 9.2) of Gly, alanine (Ala), and sodium hydroxide (NaOH) were dried at 90°C or 130°C in glass vials over durations of 1 to 120 days. The products were analyzed with liquid chromatography-tandem mass spectrometry. The longest peptides detected were 16-mers of hetero-oligopeptides and homo-oligopeptides of Gly. The longest detected homo-oligopeptide of Ala was 4-mer. The composition of the product peptides represents a substantially higher reactivity of Gly over Ala in peptide synthesis, possibly due to the limiting of nucleophilic substitution by the bulkier side chain of Ala over Gly. Higher temperature substantially promoted the rate of the oligomerization reaction but also promoted the consumption reactions of the product oligomers. Thus, when the reaction progressed, exceeding the yield maximum of the lower temperature, the yields of peptides at the lower temperature became higher than the yields at the higher temperature, showing that longer incubation times with lower reaction temperatures are favored in the synthesis of longer and more Ala-rich peptides. Thus, even if we assume the possible higher abundance of Gly over other amino acids on Hadean Earth, these results suggest that evaporative environments over geological timescales, promoted the synthesis of polypeptides that contained glycine and other amino acids such as alanine.