Recent achievements on helium isotope study are reviewed in the paper. Helium-3 is a unique nuclide which indicates a primordial signature, while most of helium-4 is produced by the radioactive decay of U and Th in crustal rocks. The ³He/⁴He ratios provide useful information on the origin of terrestrial gas and rock samples. It is confirmed that there is a close correlation between the ³He/⁴He ratio of gas and rock samples and the geotectonic structure of the sampling sites. The ³He/⁴He ratio in mid-ocean ridge basalts (MORB) as well as in thermal fluids emitting from a ridge crest is very uniform with the value of 1.2×10^-5 for samples collected at global spreading centers. The MORB type helium is considered to be representative of the Earth's upper mantle. Volcanic gases and rocks from hot spot regions such as Iceland and Hawaii indicate higher ³He/⁴He ratios than that of MORB, suggesting their deeper origin. Geographical distributions of helium isotope ratios in Japan and New Zealand show a quite similar trend: low ³He/⁴He ratio in the frontal arc region and high in the volcanic arc. The mantle helium in the volcanic arc region may be associated with the diapiric uprise of a magma. The low ³He/⁴He ratio in the frontal arc may be attributed to the accumulation of radiogenic helium in crustal rocks.

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The following differences can be recognized world-widely between the last glacial and postglacial periods. In the last glacial period, 1) δ¹³C value of benthic foraminiferal test was 0.5‰ smaller, 2) cadmium and calcium ratio of benthic foraminiferal test was about 20% higher, 3) atmospheric CO₂ content was about two-third, and 4) large amount of dust had accumulated in polar region. And also 5) calcium carbonate preservation spike had occurred during the transitional period from the last glacial to postglacial. The oceanic environmental change which can systematically explain these differences is discussed in detail.

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Rare earth element (REE) abundances in the Canyon Diablo iron meteorite were determined by the isotope dilution method using thermal ionization mass spectrometry. Isotope ratios of La, Nd, Lu, Ba and Rb were also examined, and they were found to be within the normal range. Because of extremely low REE contents, correction for blank values was necessary even after several distillation of the reagents used. For light REEs, the correction was 50 to nearly 100%, and between 10 and 20% for heavy REEs. The concentrations of REEs in the Canyon Diablo iron meteorite were about 1 to 300ppt, and the normalized values by the Leedey chondrite were approximately 10^-4;. Three REE patterns from one slice showed same positive trend toward heavier REEs, while a different slice showed a negative trend. In the sample, therefore, the REE distribution appears heterogeneous. Ce in the rhenium ribbon of center filament often interfered with the measurements of Ce. Assuming a constant intensity of the interfering beam, the least squares method gave the Ce concentration.

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To classify 252 hot springs in Akita Prefecture, We used a combination of factor analysis and cluster analysis. The factor analysis showed that six factors governed evaporated residue, temperature, and concentration of thirteen chemical components of the hot springs. Geochemical meanings of the six factors are mostly explainable. As the result of cluster analysis based on correlation of scores of the six factors, in which hot springs diluted from one source can be always group into same cluster, the 252 hot springs were classified into nine groups. Relationship of the six factors in each group suggested the genesis of hot spring. Thus, the combination of factor analysis and cluster analysis is useful for the classification of hot springs.

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Oxidation products of young kerogens isolated from seven lake sediments were analyzed for low molecular weight acids (LMW-acids: C₁〜C₂ monocarboxylic and C₂〜C₆ α, ω-dicarboxylic acids) by GC and GC/MS. The oxidation was conducted at 60℃ in 1% potassium permanganate solution for 1h. Kerogen carbon that degraded into the solution accounted for 70〜80% of the total. 17〜28% (average 22%) of the degraded carbon were LMW-acids. Oxalic acid accounted for 83〜93% (average 90%) of the LMW-acids, the rest being mostly acetic acid. Kerogens of different lakes yielded similar results both in the amount and in the composition of LMW-acids. Oxidation products of synthetic kerogens (melanoidins form amino acids and carbohydrates) and biochemical compounds (carbohydrate, amino acids, protein, and lipids) were also studied. When compared with lake kerogens in terms of amount and composition of the resultant LMW-acids, melanoidins gave the closest result. The diagram of oxalic acid yield versus oxalic acid index (OAI: amount of oxalic acid relative to the total LMW-acids ) was proposed for estimating the source materials of kerogen.

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A method for evaluation of the metal-binding ability of river water is reported. It involves a Cu titration and an ion-selective electrode detection. Scatchard's plot and two binding site model approximation was used for the analysis of data. The ability could be determined for river waters containing more than 3 mg/l of organic carbon. River waters measured at pH=6.3 in 0.1M KNO₃ gave 1〜6 μmol/l with pK=6.1〜6.9 for strong binding sites and 3〜22 μmol/l with pK=4.6〜5.4 for weak binding sites. The complexing capacity of the strong binding sites apparently correlated well with dissolved organic carbon concentration. One mg of dissolved organic carbon gave 0.21〜0.55 μmol of the capacity. Dissolved Cu concentration was also proportional to the capacity. It accounted for about 1/10 of the capacity of the strong binding sites. Combination of the present method with an adsorption onto Amberlite XAD-2 resin suggested a possibility to specify organic fractions responsible for the complex formation.

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Physical behavior of plumes in the ocean was demonstrated by model calculation with some applications to a hydrothermal plume observed in the Okinawa Trough. In a special case where the initial momentum of a plume is so large that the plume was driven mainly by the momentum, a water mass of a colder and lower salinity campared to the surrounding water was formed. In other cases, a wamer and saltier water mass was formed. Concerning the behavior of the plume cloud, some phenomena caused by the differenece between diffusivities of heat and salt were also discussed qualitatively.

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