Size distribution of dissolved organic matter (DOM) was studied in the Suruga Bay by using a tansential-flow ultrafiltration system. In this study, DOM was fractionated into three fractions, HMW (10 kDa to 0.1 µm), MMW (1 kDa to 10 kDa), and LMW (smaller than 1 kDa). Concentration of dissolved organic carbon (DOC) was highest in LMW (52.5–57.3 µM and 38.2–58.7 µM at 20 m and 800 m, respectively), followed by MMW (15.0–15.9 µM and 5.9–11.4 µM) and HMW DOM (2.1–2.7 µM and 0.5–0.7 µM). As for the samples taken at 20 m, C:N ratio of HMW DOM was lowest (9–11) among the three fractions, whereas tha of LMW DOM marked the highest values (16–18). This result indicates that HMW DOM contains more amount of nitrogen enriched organic compounds compared to LMW DOM. 0n the other hand, C:N ratio of MMW DOM at 800 m was highest (19.3–22.5) among the three fractions as for the samples taken in September and November, suggesting an intensive remineralization of nitrogen enriched organic compounds contained in MMW DOM via its export from the surface to the mesopelagic zone. Concentration of dissolved organic phosphorous (DOP) at 20 m was 0.01 µM as for HMW DOM and the corresponding value was 0.10–0.11 µM as for the fraction of smaller than 10 kDa (MMW + LMW DOM). C:N:P ratio of HMW DOM was 183:17:1 and 192:18:1 in September and November, respectively, whereas that of MMW + LMW DOM was 610:41:1 (September) and 528:33:1 (November), indicating the relative enrichment of organic phosphorous in high molecular weight DOM.

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Distribution and dissolution process of biogenic silica (BSi) were investigated in the Suruga Bay. BSi concentration in the upper 200 m changed seasonally and ranged from 0.06 to 0.82 µmol/l. Vertical distribution of BSi had some peaks and marked the minimum concentration at 200–300 m. BSi concentration increased with depth below 200–300 m. In the dissolution experiments of BSi using natural seawater, BSi concentration decreased more slowly than particulate organic carbon (POC). BSi dissolved most intensively in the surface water (20 m), following the seawater taken at 150 m and 800 m. Dissolution rate constant of BSi varied among the sampling periods, and the values during the first 14 days ranged from 0.026 to 0.052 day⁻¹ as for the surface water. Rate constant of BSi dissolution and POC degradation had similar seasonal variations under the same temperature. This result suggests that dissolution of BSi would be regulated not only by temperature but also by degradation of POC, that is, bacterial degradation of organic matrix in diatom cells. Our estimation of dissolved BSi via biological process accounts for 46–47% of total dissolution over 70 days in the surface water. This suggests that much of the BSi dissolution would be biologically mediated in marine environment.

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Nitrogen dynamics within mangrove sediments was investigated in Ishigaki Island in December, 2002. More than 95% of dissolved inorganic nitrogen (DIN)was composed of NH₄⁺, but its contribution to total dissolved nitrogen (TDN) was only 10%, whereas that of dissolved organic nitrogen (DON) was achieved to 90%. We conducted a laboratory experiment to examine decomposition of DON and total organic nitrogen (TON) in the sediments. DON decreased 89 µmol N l⁻¹ and NH₄⁺ increased 212 µmol N l⁻¹ during 14 days, though no significant change was detected as for TON. As a result, contribution of NH₄⁺ to TDN was achieved to 90%, whereas that of DON was only 10%. It clearly contradicts to the field observation and suggests the process of NH₄⁺ to remove most of NH₄⁺ from the sediments. N₂O flux from the sediment to the atmosohere was estimated as 13.2 nmol m⁻² d⁻¹ using the data of the decomposition experiment, which is consistent with the values reported as for other mangrove areas.

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This article describes an accurate method for direct determination of cadmium in seawater using an end-heated atomizer graphite furnace atomic absorbance spectrometry. To avoid interferences caused by matrix elements, ammonium nitrate and di-ammonium hydrogen phosphate were added as matrix modifiers to the sample before analysis. Experiments showed that best Cd signal was obtained fot a sample volume of 15 µl with the addition of 13 µl of NH₄NO₃ (16%) and 3 µl of (NH₄)₂HPO₄ (4%), an ashing temperature of 400–550°C and an atomization temperature fixed at 1200°C. Detection limit (3σ from ten blank replicas) was 0.013 ppb and determination limit (10σ from ten blank replicas) was 0.044 ppb.

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High vacuum line made of stainless steel and computer controlled pneumatic valves attached with a 40W CO₂ laser system capable of extracting oxygen from rock forming silicate and oxide minerals in a BrF₅ atmosphere was fabricated. The vacuum line can resist the hazardous BrF₅ reagent used for disintegrating the Si = O bonds in minerals. The oxygen, thus released, is converted to CO₂ in an O₂ → CO₂ converter using graphite heated at ~ 650°C in a platinum foil holder. We present here the results on vacuum checks, initial setting of laser, reproducibility of the O₂ → CO₂ converter, background measurements during fluorination and precautions in handling the BrF₅ reagent. The present system can withstand high vacuum conditions without appreciable leaks for intervals required to complete one cycle of measurement. However, due to the toxic nature of BrF₅ reagent, sizeable amount of background O₂ was released during the pre-fluorination of the system(~ 0.2–0.3 µmoles of O₂ for 30 minutes of fluorination). Repeated fluorination of the system considerably reduced the background O₂, however, could not be completely eliminated. Tests were also made for the functional setting of the O₂ → CO₂ converter using ampoules of external O₂ gas. Optimum conditions for conversion were determined; temperature of ~650°C, graphite grain size fraction of 1–2 mm and reaction time of 15 minutes. NBS-28 quartz standard were pre-fluorinated overnight in the reaction chamber in order to reduce the background effect. δ¹⁸O_SMOW values of 14 measurements with varying amounts of NBS-28 quartz gave 10.06 ± 1.15‰. The results indicate that a minimum sample size of 250 µg is essential to overcome the background effects. However, this amount is almost four times less than the usual amount of sample used in laser fluorination laboratories elsewhere. Also, it was found that the laser beam should be defocused for precise measurement of small grain size samples. Thus, at present, the presence of background O₂ released in the reaction chamber is hindering the application of micrometer scale measurement of oxygen isotope measurements in minerals. In order to improve the present system, the background within the reaction chamber should be reduced further.

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Climatic and environmental changes through the Paleogene are characterized by some unusual sedimentological and astronomical events. LPTM (Latest Paleocene Thermal Maximum) event is thought to have been produced by an abrupt dissociation of marine sedimentary hydrates along ocean mareins. The abrupt warming that took place 55.5 Ma is one of the pronounced climatic events in the geohistory. Sudden climate cooling event at the Eocene-01igocene boundary might have been caused by multiple or continuous impacts of extraterretrial materials. EXtraordinarily warm climate during the Eocene may have been brought by either vigorous erosion and oxidation of organic carbons exhumed from the early Himalayan orogeny, or by voluminous metamorohic CO₂ degassing due to the regional metaraorphism.
Although the first two events (LPTM and E-O boundary event) certainly affected some environmental changes during each geologic time, a longer-term effect of global plate tectonics, particularly the Himalayan orogeny, is of paramount causal importance throughout the Paleogene. I summarize these views of cause and effect for circumstantial changes on the earth surface and duiscuss about them.

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