I have obtained following results written in my 209 scientific papers. 1. The tropospheric aerosols having the residence time of about 5 days are sporadically transported with a few % of long lived stratospheric aerosols. 2. The air-sea gas exchange at the sea surface is highly controlled by air bubbles taken into the depths sometimes more than 20m, inducing the fact that the gas exchange rate of CO₂ is a few tens % at least larger than that of O₂. 3. The Pacific Deep Water can absorb the largest amount of CO₂ when its nutrients are used by photosynthesis, due to the facts that (i) it dissolved much CaCO₃ test during its stay in the deep, (ii) it was formed before the industrial revolution, and (iii) it expelled CO₂ from the surface during winter in the Antarctic Ocean. 4. The continental shelf zone shallower than 200m occupying only 8% of area of world seas is contributing about a half of the oceans' atmospheric CO₂ absorption. 5. Chemical tracers reveal one order of magnitude slower northward flow of the Pacific Deep Water than the current meter, its vertical eddy diffusivity of 1.2cm²/sec and its oldest age of 2000 years as well as 3% renewal of the Japan Sea deep water in winter 2000-2001. 6. Analyzing the oceanic behavior of radiochemical isotopes of insoluble metals, most of which cannot be collected on filter paper but settle down with great speeds, I submitted the train-passengers model for their removal from the ocean. 7. Sediment trap experiments gave the results that the organic C/carbonate C ratio is large in the western North Pacific, but it decreases with depth, indicating that the biological pump in the eastern Pacific and the Atlantic deeper than 1km is helpless. 8. In the Cenozoic era, diatoms are the strongest phytoplankton in the ocean, but their superiority disappears by reducing the concentration of dissolved silica below a threshold value due to their exclusive propagation during, for example, spring blooming, introducing the community of flagellates. 9. Mn in seawater is oxidized and removed forming particles, but it is remobilized by reducing in sediments. Repeating the processes, Mn is transported to the pelagic ocean and ferromanganese nodules are made slowly. 10. The low atmospheric CO₂ during the glacial ages is not due to the active biological production, but due to the bottom water flowing into the Atlantic and dissolving CaCO₃ followed by absorbing CO₂ at the surface as well as stronger stratification by making the bottom water dense.

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Since 1980s, elevated concentrations of As in groundwater across southern Asia have been a serious problem for over 100 million villagers relying on inexpensive shallow tubewells. The level of exposure has caused widespread illness including various cancers. Despite the magnitude of the health threat and a decade of research by numerous teams, many of the most basic factors and processes controlling arsenic within deltaic and floodplain aquifer systems remain unresolved. Particular scientific issues are, (i) ultimate source of As, (ii) physico-chemical factors controlling spatial/temporal variations of As, (iii) impact of anthropogenic activities, and so on. The aim of this review is to make clear the controversial issues in this field, and to suggest what issues are needed to clarify in near future. This review is classified into 4 chapters. Geochemical characteristics of As contaminated groundwater in Bengal Basin are firstly overviewed. In the second chapter, experimental studies related to the low temperature geochemistry of As are summarized, e.g., molecular structure analysis, speciation, and water-rock interaction. In the third chapter, previously proposed hypotheses for mechanism of groundwater As contamination are outlined. Considering the background studies, current controversial issues and future prospect are proposed in the final chapter.

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A wavelength dispersive X-ray fluorescence spectrometer has been widely used for elemental analyses in the field of earth and soil sciences. In the present study, this instrument was applied to the quantitative analysis of some major (Mg, Ca, K, P, Al, Na) and minor elements (Mn, Fe, Ba, Cr, Cu, Ni, Pb, Sr, Zn) in vegetation specimens. Standard samples for calibration were prepared by mixing geochemical reference rock samples with some reagents. Samples were melted with lithium tetraborate to prepare glass bead. Vegetation samples (Chamaecyparis obtuse, Phragmites australis, litter and reference materials) were heated at 400℃ for 4 hours in advance. We used D (Deviation) value {(Measured value)-(Certified value)}/(Certified value)×100 – to check the accuracy with certified reference vegetation materials, NIST1547 (Peach Leaves) and NIST1573a (Tomato Leaves). The D values of major elements except for Na, and those of minor elements such as Fe, Ba and Sr were within ±10%. The results of Ca and K were satisfactorily precise considering that their D values were within ±5%. The method proposed here can be reliably applied to analysis of vegetation species, and even complicated materials composed of litters and minerals in the soil horizon.

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