Hiroyuki Tsubota

Sedimentary humic acid and fulvic acid as surface active substances

Abstract Surface tension of sedimentary fulvic acid (FA) and humic acid (HA) with molecular weight from 300,000 was measured at 5°C and 25°C, over a wide range of concentrations (0.114-107.4 g/l) at pH 8. HA was in the form of sodium humate. Surface tension decreases with an increase in HA and FA concentration and both HA and FA were found to be surface active materials with FA exhibiting the lowest surface tension (31 dynes/cm). Plots of surface tension vs. log concentration gave two straight lines with a break at a certain concentration similar to surfactants. From the concentration at the break point, aggregation concentration (AGC) was determined. For HA with molecular weight above 10,000, the AGC decreased with an increase in molecular weight. The more hydrophobic the HA, the greater was the tendency to form aggregates. Surface excess (surface concentration) was determined (2.3 × 10−10−5.5 × 10−10mol/cn2) from the slope of the plot of surface tension vs. log concentration for concentrations lower than the AGC. Adsorption of HA into the surface layer increased with increasing molecular weight of HA.

Sedimentary humic acid and fulvic acid as fluorescent organic materials

Abstract Fluorescence and absorption spectra of sedimentary humic acid (HA) and fulvic acid (FA), with molecular weights ranging from 300,000, were measured at 20°C and pH 8. The maximum excitation and emission wavelengths of HA were longer than those of FA, being independent of molecular weight. The excitation and emission maxima can be utilized to differentiate between sedimentary HA and FA. It is suggested that the fluorophors in HA are of a higher molecular weight aromatic groups than those in FA. Smaller molecules were found to have a greater fluorescence than larger ones for sedimentary humic substances and this phenomenon is similar to those obtained for humic substances of terrestrial origin. The absorption coefficient (1/g/cm) of HA decreased, while that of FA increased with the increase in molecular weight. It was shown that fluorescence intensity per weight concentration unit of HA increases and that of FA decreases with increasing absorption coefficient.

Vertical distribution of fluorescent organic matter in the North Pacific

Abstract The vertical distributions of fluorescent organic matter were investigated at three stations in the North Pacific. Fluorescence intensity was low in the upper layer, and increased rapidly to a maximum at ∼ 1000-m depth. This vertical profile is similar to that of phosphate and nitrate; in the water column above the fluorescence maximum, fluorescence varies linearly with phosphate, nitrate and silicate. This is the same trend that has been reported for fluorescence and nutrients in the coastal seas of Japan. It is suggested that fluorescent organic matter is degraded in the euphotic zone and regenerated in the water column by degradation of organic matter on the settling particles as in the case of the nutrients. When deeper water was irradiated with UV light, the intensity of fluorescence decreased rapidly with time, implying that photodegradation may be primarily responsible for degradation of the fluorescent substances in the upper layers.

Behavior of natural fluorescence in Sagami Bay and Tokyo Bay, Japan — vertical and lateral distributions

Abstract The vertical distribution of natural fluorescence was investigated at one location in Sagami Bay, Japan. Natural fluorescence showed low values in surface seawater, increasing with depth. Linear relations were observed between natural fluorescence and nutrients, such as phosphate and nitrate. It is suggested that natural fluorescence resulting from marine humic substances can behave in a manner similar to phosphate and nitrate in the water column. Linear relations with negative slopes were found between salinity and natural fluorescence at several locations in Tokyo Bay, Japan. This indicates that natural fluorescence in this area results from terrestrial humic substances and is dispersed mainly by mixing of water masses. Fluorescence and absorption spectra of the seawater in Tokyo Bay showed spectra similar to sedimentary fulvic acid from Tokyo Bay. Fluorescence/absorbance ratios were nearly constant for the seawater samples in Tokyo Bay.

Cycling of soil carbon in a Japanese red pine forest I. Before a clear-felling

Cycling of soil carbon was measured synthetically and quantitatively throughout a year in two Japanese red pine forest stands on mid- and foot-slopes at Mt. Takao, Hiroshima Prefecture, west Japan. There was no distinct difference of soil temperature along the slopes, but the soil water content was higher on the foot-slope than on the midslope. The carbon flow (litterfall, soil respiration, etc.) rates were larger on the foot-slope than on the mid-slope, but there was no significant difference of the accumulation of soil carbon (A0 layer or human in mineral soil) between the areas. The results of the analysis of soil carbon cycling based on a compartment model show that the relative decomposition rate of A0 layer and humaus in mineral soil increased 1.4–1.5 fold from the mid- to the foot-slopes, corresponding to the soil moisture condition. The relative decomposition rate of A0 layer was, however, about one-third of that in a evergreen oak forest. This fact suggests that the great resistance of needle litter to decomposition is one of the main limiting factors of the cycling of soil carbon and prevents the fertilization of mineral soil in the pine forest, which was also proven by the simulation of dynamics of soil carbon cycling.

Cycling of soil carbon in a Japanese red pine forest. II: Changes occurring in the first year after a clear-felling

Cycling of soil carbon in the first year after a clear-felling was compared with that before the felling in a Japanese red pine forest in Hiroshima Prefecture, west Japan. The daily mean temperature at the soil surface in summer was increased after the felling in comparison to that before felling, and the water content of both the A0 layer and the surface mineral soil was decreased due to the loss of the forest canopy. The rate of weight loss of the A0 layer was reduced after felling. However, accumulation of the A0 layer rapidly decreased because of the lack of litter supply to the forest floor. Low soil respiration after felling was mainly caused by the cessation of root respiration. Analysis of annual soil carbon cycling was then conducted using a compartment model. The relative decomposition rate of the A0 layer decreased whereas that of humus and dead roots in mineral soil increased to some extent after felling. The accumulation of carbon in mineral soil, however, increased slightly due to the supply of humus from roots killed by the felling.

Effects of temperature on the distribution of 1-alcohols in aqueous SDS micellar solutions and ISA (Interaction of Surfactant and Additive) Coefficients

Abstract The distribution coefficients (K) of alcohols (1-butanol, 1-pentanol, 1-hexanol, and 1-heptanol) between the aqueous and sodium dodecyl sulfate (SDS) micellar phases at 40 and 55°C were determined in addition to that at 25°C. The standard free energy change (ΔG°p) of penetration of the alcohol from the aqueous to the micellar phase was obtained using the equation ΔG°p = -RT ln(K). There is a linear relation between ΔG°p and the carbon number of the alcohols, and the increment in ΔG°p per methylene group slightly decreases with increasing temperature. The standard enthalpy change (ΔH°p) and entropy change (ΔS°p) of penetration of the alcohol were estimated at 10, 25, 40, and 55°C by the use of temperature variation of the K and the Gibbs-Helmholtz equation. The fact that both ΔH°p and ΔS°p become less positive with the increase in temperature indicates that at lower temperature the penetration of the alcohol into micelle exhibits a greater entropy dependence. Estimated values of ΔH°p were compared with calorimetrical values. At 40 and 55°C, similar to that at 25°C, linear relations are observed between K and critical micelle concentration (CMC) decrease upon the addition of the alcohols. From the linear relations, ISA (interaction of surfactant and additive) coefficients defined as d ln(CMC)/dYa = (ISA)K were obtained to be −0.95 and −0.56 at 40 and 55°C, respectively, where Ya is the mole fraction of the alcohol in the aqueous phase, d ln(Q)/dXa was estimated from ISA, where Q is the degree of ionization of ionic micelles, and Xa is the mole fraction of the alcohol in the micellar phase. The theoretical value of d ln(Q)/dXa from ISA was compared with the experimental one, and a good agreement was obtained between them.

The distribution of radionuclides and some trace metals in the water columns of the Japan and Bonin trenches

Abstract Presented here is the first detailed geochemical data set on the U/Th series Th, Pa, Ac, and Pb isotopes and artificial fallout radionuclides ( 90 Sr, 137 Cs, and Pu isotopes), and some trace elements (V, Zn, Cd, Cu, Mn, and Ni) in two water columns of the Japan and Bonin trenches down to the bottom depths of 7585 m and 9750 m, respectively. Hydrographic properties such as temperature, salinity, dissolved oxygen, and nutrient content within the trench valley remain constant at the same levels as those in the bottom water of the Northwest Pacific basin (typically ∼6000 m in depth). The radionuclide activities and most trace metal concentrations are also not very different from those in the overlying water at depths of around 5000–6000 m. This means that any chemical alteration which sea water undergoes during its residence within the trench was not obviously detected by the techniques used here. The suggestion follows that the trench water is rather freely communicating by isopycnal mixing with the bottom water overlying the Northwest Pacific abyssal plain. The trench waters contain high 239, 240 Pu activities throughout, indicating that Pu is actively regenerating from rapidly sinking, large particles at the bottom interface, probably due to a change in the oxidation state. On the other hand, the vertical profiles of 210 Pb and 231 Pa show lower activities within the trench than those in the overlying deep waters, suggesting that the effect of boundary and bottom scavenging is significant in controlling their oceanic distributions. However, none of the trace metals studied here obviously follows the behaviour of the above nuclides. The 228 Th data show scattering within the Bonin Trench that is largely ascribable to analytical errors. If, however we accept that the scatter of 228 Th data is real and the variation is caused solely by decay of its parent 228 Ra, we can set an upper limit of ∼5 years for the renewal time of the trench water.

The Characteristic Distribution of Silica over the East China Sea Shelf Slope

The localized near-bottom water with silica content higher than that in the adjacent shelf water was observed to exist at the eastern margins of the East China Sea continental shelf. The core of the high silica water possessed the silica content corresponding to that in the Kuroshio at depths greater than on the shelf. The mixing analysis of water masses using temperature (T) and silica (Si) showed that the core water can be produced through the vertical mixing of intermediate water of the Kuroshio deeper than 100 m. This study provides us a conclusion that the intermediate water of the Kuroshio is strongly mixed on the shelf slope and then upwelled to form the ridge-like distribution of water masses with low temperature and high silica content at the shelf edge.

Overview of NOPACCS (Northwest Pacific Carbon Cycle Study)

The Northwest Pacific Carbon Cycle Study (NOPACCS) was a program aimed at investigating the carbon cycle of the North Pacific Ocean, which can be thought of as a large reservoir of carbon dioxide. NOPACCS was also aimed at estimating the North Pacifics capacity as a carbon sink. Project design, scientific results, and data availability, and subsequent projects resulting from this project are also described in this review. Studies of the upper ocean processes focused on the latitudinal differences in the fugacity of carbon dioxide; and on the detail of plankton community structures. Intermediate water was studied in relation to the formation of North Pacific Intermediate Water and the amount of accumulated anthropogenic carbon. The sedimentation process, past carbon cycle and coral reefs were also studied during the project. A preliminary, overall view of the carbon cycle of the North Pacific was drawn from the results of the project and compared to global values.