The 2021 eruption of Fukutoku-Oka-no-Ba (FOB) in the northwest Pacific on 13 August 2021 produced a large volume of pumice that drifted westward for ~1300 km to the Nansei Islands, Japan, and some extent. In February 2022, pumice with similar characteristics to the FOB pumice was deposited along the Gulf of Thailand. The pumice clasts deposited in Songkhla Province, Thailand, were fine-grained with <4 cm in size and rounded. Most of the clasts consisted of clinopyroxene, plagioclase (andesine), and olivine phenocrysts in a vesiculated grey groundmass, with black-coloured spots exhibiting signatures of a basaltic magma. The whole-rock compositions of the pumice are trachytic, with 61 mass% SiO₂ and 9 mass% total alkali (Na₂O + K₂O). The overall characteristics in the pumice from Thailand are similar to those in FOB pumice. These pumice in Thailand were from the 2021 FOB eruption, and drifted >2800 km south-westward across the South China Sea.

Concentrations (n = 60) and stable isotope compositions (n = 10) of mercury (Hg) were determined for sediments as deep as 2200 m below the seafloor at ODP (Ocean Drilling Program) and IODP (International Ocean Discovery Program) Site 0002C in the forearc Kumano Basin, Nankai Trough. Concentrations of Hg varied within the range of 30–240 μg/kg, except for three samples of trench-fill sediment from the accretionary prism in which Hg concentrations were 330–820 μg/kg. Range of the studied Hg concentration is similar to those of modern subareal and marine sediments. Stable isotope values were close to those of volcanogenic and hydrothermal materials: –0.26 to –0.83‰ for δ²⁰²Hg. No mass-independent fractionation was observed, as Δ¹⁹⁹Hg was almost zero (range within 0.03 to 0.1). These results suggest that the Hg originated from volcanogenic or hydrothermal detrital materials and is being accreted and/or subducted with the oceanic plate.

We conducted shipboard observations in Funka Bay, Hokkaido, Japan, in 2015, 2016 and 2019 to observe temporal variations of isoprene (C₅H₈) concentration in water and sediment. We found increases in C₅H₈ concentrations below and within the euphotic zone, which were associated with chl-a peaks and changes in nutrient and dissolved oxygen (DO). We found a C₅H₈ peak in the subsurface layer within the euphotic zone at 20–30 m depth in May–June 2019 that coincided with a decrease in DO, suggesting that there was net oxygen consumption. We hypothesize that the rapid cycle of regenerated production in the subsurface layer in early summer resulted in C₅H₈ production (1.00–1.75 pmol (μg chl-a) d^–1 at 30 m), decreased DO, relatively high chl-a levels, and nutrient depletion. We propose that C₅H₈ can be used as a new chemical parameter reflecting primary production, in addition to the common parameters of chlorophyll-a, nutrients, and oxygen. We attributed a C₅H₈ peak at the surface in May–June 2019 to photosynthetic production of C₅H₈ associated with new production, likely stimulated by the sporadic input of nutrients to the sea surface. In addition, this is the first study to report the presence of C₅H₈ in seafloor sediments. We found very high C₅H₈ concentrations in the sediment from the surface to 5 cm depth. We propose that C₅H₈ production and degradation by the bacterial community in coastal marine sediments are approximately in balance.

In this study, computer simulations were performed on ionic solutions containing heavy metal ions Pb(II), Cd(II) and As(III). The situation where these aqueous ions are retained through the sand/graphene oxide column is simulated. The sand/graphene oxide separation column is formed by the aggregation of constructed sand particles and graphene oxide (GO) molecular clusters. The process of ion aqueous solution flowing through the column is investigated and the mobility of each ion is evaluated. The simulation shows that adding GO to the sand can separate the heavy metal ions more effectively. The sequence of the mobility of the simulated heavy metal ions in the column is: As(III) > Cd(II) > Pb(II), which is consistent with the experimental results reported in the literature. We use simulation methods to study the electrostatic interaction between heavy metal ions and GO sheets. It is found that this interaction is an important factor in the separation of sand/GO column.

Slab-dehydrated fluid is considered to be involved in island arc magmatism. In this study, Li isotope ratios were determined for deep groundwater samples from the non-volcanic forearc region of SW Japan. The contribution of the slab-dehydrated fluid from the Philippine Sea Plate (PHS) was investigated in the Arima area and the eastern Kii Peninsula area, corresponding to the slab depths of ~60 km and 20–30 km, respectively. In the Arima area, the high-temperature thermal waters with high salinity called the Arima-type fluid were clarified to have low δ⁷Li values of +1–+3‰. The low δ⁷Li values with high Li concentrations are thought to be the result of fluid-rock interactions at high temperatures, which is consistent with the characteristics of the slab-dehydrated fluid. On the other hand, the δ⁷Li values of deep groundwaters in the eastern Kii Peninsula showed a wide range of +2 to +29‰. Several groundwater samples had a similar chemical property to the Arima-type fluid: low δ⁷Li values, low Cl/Li ratios, and ⁸⁷Sr/⁸⁶Sr ratios around 0.708–0.710. They are distributed along the Median Tectonic Line (MTL) and within about 20 km south of the MTL. These results indicate a common supply of slab-dehydrated fluids to the non-volcanic forearc region in SW Japan from PHS along the large faults, and Li isotope ratios will be a useful indicator to detect their contribution.

The Central Indian Tectonic Zone (CITZ) is major E-W trending suture zone between Northern and Southern Indian crustal blocks. The southern portion of the CITZ comprises three litho-tectonic units: Tirodi Gneissic Complex (TGC), Sausar Mobile Belt (SMB) and Bhandara-Balaghat Granulite Belt (BBGB). Elemental and isotopic data are used to constrain the genesis of granitoids and their protoliths, which may help us to understand the Proterozoic crustal evolution in CITZ. Geochemical and isotopic results are consistent with previous studies that these granitoid plutons are linked to the felsic magmatism of the Columbian crustal assembly in India, North America and North China. Granitoids varies from tonalite to granite, alkalic to calcic, metaluminous to peraluminous composition. Normalized elemental ratios of La/Sm, La/Yb, La/Lu, and Gd/Yb depict variable LREE enrichments and varying degrees of partial melting of heterogeneous crustal/lithospheric sources. The studied rocks are characterized by positive anomalies for Pb and negative anomalies for Nb, Sr, P, Ti, which indicate the influence of subduction-zone fluids in the source regions. Negative anomalies for K, Sr, and Ti for SMB and BBGB granitoids may also be attributed to K-feldspar, plagioclase, and Fe-Ti oxide fractionation. However, TGC porphyritic leucogranites display K, Ba and Eu positive anomalies, probably related to the accumulation of K-feldspar phenocrysts. Nd-Sr data presents initial ratios of ¹⁴³Nd/¹⁴⁴Nd t = 1.6 Ga ranges between 0.509961 and 0.510300; ε_Nd t = 1.6 Ga ranges from –5.3 to –11.9 with T_DM ages ranging from 2.20 to 2.78 Ga for TGC granitoid. The ratios of ¹⁴³Nd/¹⁴⁴Nd t = 1.6 Ga ranges between 0.510232 and 0.510985; ε_Nd t = 1.6 Ga ranges from +0.2 to +8.2 and T_DM ages varies from 1.5 to 3.0 Ga. The initial ⁸⁷Sr/⁸⁶Sr t = 1.6 Ga ratios ranges between 0.699834 and 0.797151 for SMB granitoid. However, BBGB granitoids show the ratios of ¹⁴³Nd/¹⁴⁴Nd t = 1.6 Ga ranges between 0.509752 and 0.510910; ε_Nd t = 1.6 Ga ranges from +6.7 to –16, and T_DM ages range from 1.51 to 3.29 Ga. The initial ⁸⁷Sr/⁸⁶Sr (t = 1.6 Ga) ratios varies between 0.705096 and 0.717440. These ranges of ε_Nd (t) and T_DM values possibly indicate their derivation from enriched and heterogeneous crustal/lithospheric sources, and minor components from depleted lithospheric sources.