One hundred and eight samples of daily precipitation on Ishigaki Island were collected from Dec. 4, 1997 to Dec. 5, 1998 and were analysed for chemical and isotopic compositions. δD and δ¹⁸O values of daily precipitation ranged from -82 to 11‰ and -12.1 to -0.5‰, respectively. These values were higher in winter than in summer. The d value (d=δD-8δ¹⁸O) ranged from 7 to 35 and showed seasonal variation in which it was high in winter and low in summer. This indicated that precipitation of the winter season on Ishigaki Island is derived from the continental cold airmass. Amount effects of precipitation on isotopic composition were observed throughout the year. Furthermore two trends of amount effects were observed in summer. High concentrations of chemical components were found in precipitation with high wind velocity caused by typhoons and the seasonal winds in winter on Ishigaki Island. In particular, the typhoons significantly increased the concentration of chemical components. Annual average of Cl^- concentration was nearly equal to the Cl^- concentration in winter precipitation along the Sea of Japan side on Honshu Island, and the annual deposition rate of NaCl was about 7 times larger than the national average. The calcium ion of non sea salt origin in precipitation is probably supplied through the dust containing CaCO₃ from the limestone-rich soil of Ishigaki Island and NH₄⁺ by chemical fertilizers used in the island. The annual average value of the NO₃^-/nss SO₄^2- ratio, 0.64, was twice as larger as the ratio of Tokyo (0.35). It may be caused by photochemical reaction forming nitric acid in Ishigaki Island under the strong insolation of the subtropical climate. High concentrations and large deposition rates of nss SO₄^2- were observed in fall to winter, when d values of precipitation were high. The ratio of NO₃^-/nss SO₄^2- was observed to be low in winter on Ishigaki Island. This indicated that the sulfuric acid was transported from the Asian Continent to Ishigaki Island by the continental cold airmass. The pH ranges from 4.1 to 6.9 and its annual mean was 5.4. This mean value of pH was higher than those of Honshu Island (e.g., Tokyo 4.7). Nss Ca²⁺/NH₄⁺ ratio, 1.7, was much higher than those of Honshu Island (e.g., Tokyo 0.33). This suggests that nss Ca²⁺ is main acid neutralizer rather than NH₄⁺. This result reflects the environmental characteristics of Ishigaki Island which is covered with limestone-rich soil.

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Long-term changes in the concentration of arsenic in these 40 years were investigated for four hot springs, Kusatsu-Yubatake, Bandaiko and Kagusa No. 3 and No. 8, located in the Kusatsu hot springs area in the eastern foot of Kusatsu-Shirane volcano, Gunma, Japan. The drastic increase in arsenic content was observed only in Bandaiko between 1985 and 1998. The concentration of arsenic in Bandaiko water showed good positive correlations with those of iron and sulfate ions during that period. In addition, the arsenic content has fluctuated equimolecularly with that of iron through the period. This suggests the major origin of the dissolved arsenic in Bandaiko water is arsenopyrite. The drastic increase in the concentration of arsenic probably have been caused by the accelerating oxidation-dissolution of arsenopyrite present in and around underground hydrothermal reservoir, which started in 1970 since the hot spring issued out, associating with the continuous intrusion of meteoric water containing a considerable amount of dissolved oxygen. The concentration of arsenic in Bandaiko water is now around 10 mg dm^-3, meaning that the annual supply of arsenic from Bandaiko water is about 49 ton y^-1. Bandaiko is by far the largest arsenic supplier in the Kusatsu hot springs area.

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Silicon, supplied mainly from lands, plays an important role in the primary production in the oceans. In this study we have conducted the observation of dissolved Si concentration in river water along the Tamagawa river throughout a year and spotted two zones which showed statistically significant change in the dissolved Si concentration: the Ogouchi Dam and the discharging zone of treated water from sewage treatment plants. On average, the former removed 0.8 mg/l of Si from the upper stream water containing Si at a concentration of 6.40 mg/l, whereas the latter added 1.2 mg/l of Si to the river water. The removal of Si in the dam might be attributed to diatom intake of Si in the dam, although the relation between the Si removal and its number density was insignificant. The addition of Si by the sewage treatment plants is likely due to the use of groundwater having a higher concentration of Si in the municipal areas, from which the treatment plants collected sewage, according to the consistent results of a simple mixing calculation. The annual removal of Si by the dam is estimated to be 250 ton/year and the annual load by the six sewage treatment plants is as much as 1,100 ton/year, implying that the anthropogenic input of Si along the river flow. Considering P and N concentration changes, however, N/Si and P/Si markedly increased to exceed the Redfield ratio by the addition of the treated water from the sewage treatment plants. This suggests that the anthropogenic activities along the Tamagawa river give an advert effect on diatom in the coastal area with respect to the mutual concentration of the three nutrients.

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Rare earth element (REE) contents and mineral assemblages of weathered granitic soil (crust) in the Ashizuri-misaki area, have been investigated in order to evaluate potential REE resources. The weathered soil with maximum thickness of about 5 meters formed at the surface of the Middle Miocene granitic rocks which consist mainly of quartz syenite and alkaline and fluorine-rich granite with high content of light REE such as La and Ce. In the weathered soil, chlorite, gibbsite, and kaolinite are pronounced when compared with the underlying granitic rocks, which mainly resulted from the decomposition of biotite and plagioclase during a weathering process. Almost all the quartz and K-feldspars in granitic rocks are, however, preserved during a weathering. The weathered soil in the Ashizuri-misaki area records the average Σ REE + Y value of 342 ppm with maximum contents of ΣREE + Y 701 ppm. The REE contents, especially light REE with exception of Ce and Eu, of the weathered soils are slightly depleted than those of the underlying granitic rocks. The depletion is considered to be caused by a leaching of LREE from LREE-bearing minerals such as chevkinite and fluocerite. The REE contents within the weathered soils reflect mainly residual REE-bearing minerals such as zircon and Nb-bearing multiple oxides which are originated in the granitic rocks. Enrichment of REE which is equivalent to the ion-adsorption style REE deposits in southern China is not expected to occur in the weathered soil within the granitic rocks in the Ashizuri-misaki area.

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To obtain implications for the vertical water mixing within the Sea of Japan, we collected 29 water samples from 2 sites around the Yamato Ridge (3,685 m and 2,610 m depth), and 24 samples from coastal areas (12 sites) along the Japan Island (85-475 m depth) in May-June 2004 and 2005. ²²⁶Ra (t_1/2=1,600 y), ²²⁸Ra (5.75 y) and ¹³⁷Cs (30.2 y) were quantitatively coprecipitated by BaSO₄ and AMP using 20-60 L of water samples, and their activities were measured by low-background y-spectrometry. From surface to the Upper Proper water (1-1,000 m), the ²²⁶Ra and ¹³⁷Cs activities exhibit gradual decrease from 1.8-0.2 mBq/L and 1.7-0.2 mBq/L, respectively. From the gradient of ²²⁸Ra activity, the vertical eddy diffusivity was calculated to be 〜6 cm²/s around the Yamato Ridge. In the Deep Proper Water (>1,000 m), the ²²⁸Ra activity keeps approximately constant (〜0.2 mBq/L). These vertical distributions are reflecting the intense vertical mixing compared with those in other oceans. For deep sites of coastal areas (>〜250 m depth), the ²²⁸Ra activities of bottom waters are notably lower (〜0.5 mBq/L) than those of shallow sites (<〜250 m) (0.7-2.2 mBq/L). The exchange of radium between shallow and deep water is inhibited by the boundary layer (thermocline at 〜250 m depth).

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Large consumption of fossil fuels has marked the 20th century, resulting in significant introduction of CO₂ into the atmosphere with its concentration increasing from a pre-industrial value of about 280 ppm in the 18th century to about 380 ppm at present and predicted further increase. Global warming related to excess emission of carbon dioxide is a burning issue for the world's environment nowadays. In turn, carbonate sediments are common and abundant in earth's surface environments. Carbonate rocks such as limestone and dolomite are a sink for extremely large amounts of carbon compared with atmospheric carbon dioxide. The mass fluxes between the atmosphere and oceans are partly controlled by reactions between carbonate minerals and natural waters. Therefore, it is potentially important to study carbonate geochemistry for understanding global and local environmental issues. The pioneer work on carbonate geochemistry in Japan was first performed by Minami and Honda at the University of Tokyo in 1942. They reported Sr/Ca in carbonate sediments and discussed the aquatic geochemical cycle of Sr-Ca (Minami and Honda, 1950). They also pointed out that Sr and Ca occur together in marine carbonates such as coral and provided a Sr/Ca value of 1.0 % (atom ratio) which is recognized as a very precise value even now. Under their great insight, they succeeded in estimating the Sr contents of stalactites and stalagmites to be 〜0.001% (w/w), even though they had no methods which could analyze Sr at such low contents (Marvin, 2003). The pioneer work by Minami and Honda might encourage Japanese carbonate geochemists to start their studies on polymorph of carbonates and the distribution of trace elements about 50 years ago. Over half a century has passed since the pioneer work. The latest technical developments of sophisticated equipment such as ICP-AES, ICP-MS, TIMS and SIMS make it possible to determine ultra-trace amounts of target elements or compounds and precise isotope ratios and also provide significant information on the palaeo environment in which the carbonate mineral was formed. In this issue, recent studies on carbonate geochemistry were compiled as a memory of the annual meeting of the Geochemical Society of Japan, held at University of the Ryukyus in September 2005. Among 22 subjects presented as oral (15) and poster (7) in the special session of carbonate geochemistry, eight selected papers are presented here. We hope these papers could help for better understanding of carbonate geochemistry associated with environmental changes.

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Massive hermatypic corals are one of the most excellent archives for reconstructing paleoclimatic and paleoceanographic changes because they commonly live in shallow tropical and subtropical oceans, grow at a rapid rate, and contain a remarkable array of geochemical tracers within their skeletons. In particular, oxygen isotopic composition and Sr/Ca ratio of coral skeletons have been used as proxies for past thermal and hydrological variations in sea surface conditions. Recent investigations on geochemical records of modern long coral cores provide continuous time series of sea surface temperature and salinity in many tropical regions, which document climatic variability on interannual and decadal to multidecadal timescales (El Nino/ Southern Oscillation, Indian Ocean Dipole mode, and Inter-decadal Pacific Oscillation), volcanic eruptions, and global warming. However, high-resolution paleoclimatic records of coral skeletons over the last several centuries are spatially limited and the mechanisms causing the climatic variability remain unclear at present. High-fidelity paleoclimatology should be progressed in order to expand our knowledge on the nature and causes of global climatic changes.

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The oxygen and carbon isotopic composition of shallow-water carbonates and their fossil components can be important tools for understanding Quaternary paleoceanographic conditions of marginal seas, including coral reef regions. However, recent paleoceanographic studies using isotopes have been based on pelagic or hemipelagic sediments because the original δ¹⁸O and δ¹³C values of shallow-water carbonates are normally altered by post-depositional diagenesis. This study shows that marginal- to open- ocean isotopic signals can be preserved in carefully cleaned low-Mg calcitic planktic foraminifers of shallow-water carbonates, even when the isotopic values of the carbonate host rock have been altered by meteoric fluids and subaerial exposure. Subsequently, the downcore δ¹⁸O change of planktic foraminifers in Pleistocene shallow-water carbonates (the Ryukyu Group) can be used for the oxygen isotope stratigraphy. By com- parison, whole-rock measurements provide information that records the diagenetic signals, such as negative δ¹³C spikes indicating horizons of subaerial exposure.

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Components in biogenic carbonates have been recognized to be attractive tools for reconstructing past oceanographic and climatic changes. Although chemical components in coral aragonite are precipitated away from equilibrium, fluctuations of Sr/Ca ratio in coral skeletons have been empirically considered to be controlled by temperature. Thus, Sr/Ca ratio in coral skeletons has been applied for paleoclimate reconstruction. Recently, coupled measurements of coral skeletal δ¹⁸O, indicator of both SST and seawater δ¹⁸O, and Sr/Ca ratio are used to reconstruct seawater salinity as well as SST. On the other hand, it has been reported that Sr/Ca is also affected by growth rate of coral skeleton besides SST. However, the impact of skeletal growth rate on Sr/Ca ratio is a matter of debate and controversial results have been reported at the present. In this review, recent progress of studies on the topics and a mechanism of growth rate-related Sr/Ca variation based on a physiological model are summarized.

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Reef-building corals are distributed in the tropical and sub-tropical oceans and can be found as fossils in a significant fraction of the geologic record extending back to the middle Triassic. Their skeletons continuously grow up to one of the largest biological architectures on the earth, which support various marine lives in nutrient poor regions. Moreover, recent global warming gives corals another importance as powerful tool to reconstruct paleoclimate recorded in their skeletons with high-resolution. Understanding mechanism of coral biomineralization is crucial and common subject among interdisciplinary fields including geology, paleontology, biology, geochemistry, climatology and material science. However, exact mechanism of calcification processes is still poorly understood. For better understanding of coral biomineralization, we need to put structural, physiological and bio-geochemical information on very small space in calcification site. Most recently, significant progress and novel technique have been developing in several related fields. For example, microanalytical methods with nano- to sub-micronmeter scale, observations of nanometer size grains in coral microstructures, and a novel coral culture technique have been developed during last several years. By combining these new skills, it is now possible to observe biogeochemical signs within ultra fine structures in coral skeletons. Such new combined approaches hold the promise of yielding important new insights into the various biomineralization processes.

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Sr/Ca and Mg/Ca ratios of coral skeletons have been used as proxies for past changes in sea surface temperature of tropical and subtropical oceans. Microanalytical methods such as electron probe micro-analyzer (EPMA) and secondary ion mass spectrometry (SIMS) may provide chemical heterogeneities for Sr/Ca and Mg/Ca ratios, which cannot be explained by the temperature variations. In order to validate these heterogeneities, it is necessary to evaluate the microanalytical methods by comparing data with a conventional method using chemical dissolution and inductively coupled plasma atomic emission spectrometry (ICP-AES). We have measured Sr/Ca and Mg/Ca ratios of coral skeleton collected in Ishigaki island, southwestern Japan by EPMA, SIMS and ICP-AES methods. All data are consistent with each other within experimental errors, showing that there is a significant seasonal variation. EPMA and SIMS methods are probably useful in a paleoceanographic study. We have also determined Ba/Ca and U/Ca ratios by SIMS. U/Ca ratio shows a positive correlation with Sr/Ca ratio. Among these analytical methods, SIMS may be superior when its accuracy is improved, since the lateral resolution and sensitivity of minor and trace elements are the highest.

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Reagent grade calcite was reacted with MgCl₂ solutions doped with REE (Mg concentration of 0.089M-1.8M and REE concentration of about 0.3 ppm each) at 150℃ for 10 or 20 days. Solid products were identified by X-ray diffraction. Solid and liquid phases were analyzed for Mg, Ca and REE. The solid phases reacted with MgCl₂ solutions (0.89M and 1.8M of Mg²⁺) were almost magnesite (about 95%). The molar ratios of Mg/(Mg + Ca) in solutions of the run products were consistent with the extrapolation of the reported experimental equations in the high temperature range from 275℃ to 420℃ to lower temperatures. The values of pH at room temperature of the final solutions are ranging from 5-7, and they show a decreasing trend with increasing Mg concentration. This is probably caused by the precipitation reaction of brucite, which is more likely to occur at 150℃ than at 25℃. The REE partition coefficients between solid and liquid phases defined by K_d(REE)={X_REE/(X_Mg+X_Ca)}_solid/{[REE]/([Mg]+[Ca])}_liquid have been determined experimentally. The series variation of logK_d (REE) in the run in which the solid phases were almost magnesite, shows a decreasing trend in LREE and a convex tetrad effect.

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Speleothems record successive information on terrestrial paleoenvironment. The vegetation change in the Akiyoshi-dai Plateau, Yamaguchi Prefecture, was examined using the δ¹³C values of a stalagmite formed in the grassland area. The stalagmite δ¹³C values largely reflect those of the soil CO₂ derived from organic carbon associated with the δ¹³C values dependent on the vegetation type. The soil δ¹³C values in the forest areas (-23〜-21‰) were lower than that in the grassland area (-15‰). A 50/50 contribution from rock carbonate (+3‰) and the soil CO₂ resulted in HCO₃^- with δ¹³C values reflecting the vegetation. When the seepage water was exposed to cave air of a lower CO₂ concentration, the speleothems were formed from the water in the cave. The δ¹³C values of the speleothems in the forest areas were in the range of -7.8〜-5.5‰, whereas that in thegrassland area was -4.3‰. The 7 cm growing stalagmite sample from the Kitayamakita-no-yokoana Cave in the grassland was found to have recorded the artificial vegetation change in the Akiyoshi-dai Plateau as variations in the δ¹³C values of the carbonate. The average growth rate of a separate stalagmite (24μm y^-1) formed under circumstances similar to the stalagmite examined in the Akiyoshi-dai Plateau made it possible to estimate that yearly burning of the dead grass on the Akiyoshi-dai Plateau had started about 400 years ago.

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Trace amounts of Cd, Ni, Cu, and Pb in the Triassic limestone samples from the Nakijin-jo Site and Cape Hedo of Okinawa-honto Island were determined by flame atomic absorption spectrophotometry combined with the ammonium pyrrolidinedithiocarbamate (APDC) - 4-methyl-2-pentanone solvent extraction system. Positive relationships were observed between the contents of trace metals (Mn, Ni, Cu, Zn, and Pb) and those of acid-insoluble residues (mainly SiO₂) and Fe. This fact suggests that these metals exist in accessory minerals such as silicates and pyrite in the above limestone samples. On the contrary, no positive correlation was observed between the Cd and Fe contents, indicating that Cd may differ in its behavior from the above metal ions during the deposition and diagenesis of limestones. Cadmium is almost always present as 1 mol dm^-3 acetic acid-soluble form in the examined samples. This suggests that Cd²⁺ is incorporated into calcite by replacing Ca²⁺ in the lattice. The arithmetic means of Cd in the Nakijin-jo Site and Cape Hedo limestone samples were 0.19 and 0.30 ppm, respectively. The value (0.30 ppm) of the Cape Hedo limestone samples with a small amount of acid-insoluble residues is similar to the average Cd contents of three Middle or Upper Triassic limestones from different localities. The Cd contents of Triassic limestones are lower than those of Permian limestones, but slightly higher than those of Quaternary ones.

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