This paper review the organic geochemical studies on the Greenland (Site-J) and Antarctic (H-15) ice cores. Water-soluble dicarboxylic acids (e.g., oxalic, succinic and azelaic acids) and lipid class compounds (e.g., n-alkanes, PAHs, fatty acids, etc) have been analyzed using a capillary gas chromatography (GC) and GC/mass spectrometry. Their molecular distributions and concentrations were used for the reconstruction of the past atmospheric changes over several hundreds years. Fatty acids in the both ice cores showed a strong even/odd carbon number predominance with two maxima at C₁₆ and C₂₄ or C₂₈. In the Greenland ice core, lower molecular weight (C₁₂-C₁₈) fatty acids stayed constantly low in the 16^th to 19^th centuries. However, they significantly increased in the 20^th century with sharp peaks in the 1930s to 1950s and 1980s, suggesting an enhanced sea-to-air emission of marine organic matter and subsequent transport over the Greenland ice sheet. The lower concentrations in the 1500s to 1800s (a period of Little Ice Age) were interpreted as a depressed emission from the ocean due to the enhanced sea ice, whereas higher concentrations in the 1900s as an enhanced emission due to the global warming. Concentrations of azelaic acid, a specific photooxidation product of biogenic unsaturated fatty acids, showed a sharp increase in the early 1900s to 1940s in the ice core. This was interpreted by a combination of more sea-to-air emission of marine algal lipids and more atmospheric oxidation of the precursors by the enhanced atmospheric oxidizing capability due to the global warming. Concentrations of PAHs in the Greenland ice core showed a rapid increase in the 20^th century due to the enhanced human activity. On the other hand, concentrations of azelaic acid in the Antarctic ice core showed a sharp increase after the 1970s, although azelaic acid and unsaturated fatty acids are less abundant than the Greenland ice core. This finding has been explained by a hypothetical mechanism, that is, atmospheric oxidizing capability over the Antarctica has increased recently as a result of ozone depletion in the stratosphere. Ice core records of various organic species were found to be linked to climate changes, and thus, to be used as a useful tool for the reconstruction of the atmospheric changes in the past.

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Changes in fatty acid composition of marine particulate matter indicate the species succession and the growth physiology of phytoplankton population. The fatty acid is a useful indicator for characterizing sinking organic matter from phytoplankton bloom. The sinking particles derived from aggregates of bloom forming phytoplankton have large fluxes and different organic matter quality when compared to those in non-blooming periods.

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Carbon isotopic compositions (δ¹³C values) of sterols in various geochemical samples were analyzed and their usefulness as a biomarker was evaluated. δ¹³C values of algal derived sterols ranged from -25.3 to -22.1‰ in Holocene sediments, while they ranged from -29.7 to -24.2‰ in glacial marine sediments, suggesting that the δ¹³C values are mainly depend on the primary productivity. The δ¹³C values of 24-methylcholesta-5,22-dien-3β-ol in Japan Sea sediments ranged from -25.2 to -23.1‰. This sterol is derived from bacillariophyceae (diatom) and haptophyceae. However, the carbon isotopic compositions of unsaturated C₃₇ ketones (C₃₇ alkenones) are largely different from that of 24-methylcholesta-5,22-dien-3β-ol. The δ¹³C values of cholesterol which is produced partly by zooplankton ranged from -24.5 to -21.5‰. The δ¹³C measurements of C₂₉ sterols are valid for the discrimination of their sources (marine and/or terrestrial) and this would provide a powerful tool for discussing the paleo-climatic changes in the Japan Sea.

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Thirty-two crude oils from five oil fields in the Kosei area, Akita Prefecture, can be classified into five groups based on their API gravity, sulfur content, sulfur isotopic composition and V/Ni ratio. These geochemical characteristics offer important constraints on petroleum migration and accumulation in the area, because they reflect maturity and depositional oxic/anoxic condition of source rock, migration processes, biodegradation and so on.
This study suggests that both sulfur isotopic composition and V/Ni ratio are useful oil classification parameters.

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Twenty two steranes and 17 triterpanes were detected in the Cretaceous-Tertiary (K/T) boundary sediments at Kawaruppu, Hokkaido, Japan. These steranes and triterpanes were detected at a concentration level of 0.001-0.1nmol g^-1. Their concentrations were smaller within the K/T boundary claystone than in the sediments above and below the claystone, which are likely related to the large biomass extinction event at the end of the Cretaceous. The concentrations of 5α-cholestane and the relative ones of 17α,21β-hopane in the sediments above the boundary claystone were about a half of those in the sediments below the claystone, whereas those of 5α-ergostane, 5α-stigmastane, and oleanane in the sediments above were less than a half abundance level of those in the sediments below the claystone. Diastereomer ratios of steranes and triterpanes were nearly constant over the sediments. No tricyclic alkanes were detected in the sediments.

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A mathematical model has been proposed to obtain depth profiles of compound abundances (release extents) released from thermal decomposition of kerogen in a sedimentary sequence using parameters for reaction kinetics in the decomposition and for thermal history of the sequence. Equations for release extents and differential release extents of compounds were derived from a rate law of first-order reaction and the Arrhenius expression. The model was applied for the Neogene Shinjo sediments, whose depths were reported by Taguchi et al. (1986). The activation energies and pre-exponential factors for benzene, hexane, toluene, phenol, heptane and indene on release from kerogen were reported by Oba et al. (2002). The geothermal gradient was determined by the method by Suzuki (1984) and data by Suzuki and Shimada (1983), and the rate of the sediment subsidence by Shiraishi and Matoba (1992). The depth profiles of differential release extents for compounds were different in temperature (therefore, depth) from each other. The average temperatures of the maximum releases were 134℃ for benzene, 159℃ for hexane, 136℃ for toluene, 143℃ for phenol, 152℃ for heptane, and 121℃ for indene. The temperatures for benzene, toluene and indene appear in the petroleum generation zone and for the rests below the zone. Furthermore, the model indicated that hexane and heptane of aliphatic hydrocarbons were released in sediments deeper than benzene, toluene and indene of aromatic ones. These calculated depth profiles were similar in pattern to those reported for solvent extractable aliphatic and aromatic hydrocarbons in the sediments, but shifted toward deeper sediments than the reported profiles. These shifts may be corrected by taking consideration of the effect of sediment constituents for the determination of parameters for reaction kinetics.

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Enormous methane gas hydrate is expected to be in the surface sediments over accretion prisms of Nankai Trough. Methane in gas hydrate is generally of biogenic origin produced by microbial fermentation. However, thermogenic gas can contribute to the formation of gas hydrate especially in Nankai Trough, since thick sedimentary rocks more than 5000m are distributed below the possible gas hydrates in this area. In the present study, hydrocarbon gases trapped in the sedimentary rocks with and without calcite veins and carbonate concretions collected from the Paleogene Otonasigawa Group in the Shimanto Terrain, Kii Peninsula were preliminarily analyzed to evaluate the upward migration of thermogenic gas.
Hydrocarbon gases were recovered from the sedimentary rocks by whole rock pulverization method. The sedimentary rocks with calcite veins are generally rich in hydrocarbon gases showing that they are mainly present in fluid inclusions of calcite veins. Significant amount of hydrocarbon gases is also detected in carbonate concretions. These hydrocarbon gases generally contain significant ethane, showing their thermogenic origin. Calcite veins and carbonate concretions formed in sediments over the accretion prisms of Nankai Trough can trap thermogenic hydrocarbon gases migrating upward.

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In order to investigate environmental pollution, the surface sediments of Lake Kawaguchi were analyzed for various hydrocarbons. The sampling was carried out at the western and the eastern basin of Lake Kawaguchi to compare with them. CPI (C_<13>-C_<35>) values of n-alkanes, the αβ/(αβ+ββ) ratio of C_<31> hopane and the concentration of PHAs were used for evaluation of pollution. Three kinds of molecular markers indicate that the eastern basin is more polluted than the western basin. The influence of an asphalt pavement developed on a circular road around the lake in 1938 was detected in the sediments at the depth of 13〜14cm from western basin, and 18〜19cm from the eastern basin.

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