On 1 January 2024, an M7.6 earthquake occurred in the northern Noto Peninsula, Japan, following prolonged earthquake swarm activity that has been suggested to involve subsurface fluid migration. To provide geochemical constraints on the nature and origin of such fluids, we analyzed lithium (Li) and strontium (Sr) isotope systematics of waters from the Noto Peninsula, with a primary focus on hot spring waters that are considered to reflect fluids circulating through deeper parts of the crust over long residence times. River water (MSK) and non-thermal shallow groundwater (KWS) were analyzed as reference samples representing surface and shallow groundwater components. The hot spring waters are characterized by high Cl/Li ratios (>1,000) and relatively high δ⁷Li values compared with volcanic and forearc deep-derived fluids reported from southwestern Japan. These geochemical features suggest that the sampled hot spring waters do not record a dominant volumetric contribution from high-temperature deep fluids such as magmatic or slab-derived fluids. Instead, the Li–Sr isotope systematics suggest extensive interaction with crustal rocks and mixing with ancient seawater that infiltrated the crust during the Miocene opening of the Japan Sea and was subsequently modified during long-term subsurface residence. Time-series observations of δ⁷Li and Li/Sr ratios at selected hot spring sites reveal short-term temporal variations in fluid composition. However, these variations do not show a consistent temporal correspondence with individual seismic events, nor are they accompanied by systematic changes in ⁸⁷Sr/⁸⁶Sr ratios. This indicates that the observed fluctuations reflect transient changes in mixing proportions among crustal fluids and ancient seawater components rather than episodic input of a distinct deep-fluid endmember. Overall, this study provides geochemical constraints on the origin and evolution of subsurface fluids beneath the Noto Peninsula. Although previous studies have suggested the involvement of deep-seated fluids in the seismic activity of the region, the hot spring waters analyzed here indicate that such high-temperature deep fluids are not directly expressed in the shallow hydrothermal systems sampled.

Ryugu samples and carbonaceous chondrites contain organic matter that is expected to record the molecular evolution from the presolar stage to the early Solar System. In contrast to CI chondrites, Ryugu samples are well suited for investigating pristine organic components because they have not undergone terrestrial weathering. In this study, we analyzed volatile organic components released from Ryugu grains by vacuum pyrolysis and gas chromatography/mass spectroscopy (GC/MS). Two of three Ryugu grains released volatile organic fragments at ~80–120°C; however, such releases were not observed in other carbonaceous chondrites. The GC/MS of released gases from another Ryugu grain revealed that the gases were dominated by ethanol, with a concentration of ~100 μmol/g, while other components were scarcely detected. We found that O-rings used to seal a Facility to Facility Transfer Container (FFTC) that had been used for sample transportation contained ethanol absorbed during cleaning. Transportation tests of blank samples revealed that blank samples transported using FFTC released markedly more ethanol than those transported in a container without an O-ring. These results indicate that the O-rings of the FFTC were the contamination source. Ethanol derived from O-rings was likely trapped in the interlayers of phyllosilicates in Ryugu samples and released via heating in vacuum. This contamination could affect the reported bulk abundances and isotopic compositions of carbon and hydrogen in Ryugu samples. Further investigations using intact Ryugu samples are expected to clarify the representative characteristics of Ryugu.