Study of the effect of water-soluble fractions of heavy-oil on coastal marine organisms using enclosed ecosystems,mesocosms

Mesocosm facilities composed of 4 experimental and 2 reservoir tanks (1.5 m in diameter, 3.0 m in depth and 5 tons in capacity) made of FRP plastics, were constructed in the concrete fish rearing pond in the Fisheries Laboratory, The University of Tokyo. The water-soluble fraction of Rank A heavy residual oil was formed by mixing 500 g of the oil with 10 l of seawater, which was introduced to the 5000 l-capacity tanks. Experimental Run 4 was conducted from May 31 to June 7, 2000. Oil concentrations in the tanks were 4.5 microg/l called LOW, and 13.5 microg/l, called HIGH tank. Bacterial growth rates very quickly accelerated in the HIGH tank just after the loading of oil which corresponded with a high increase of bacterial cells in the same tank after 2 days. Later, bacterial numbers in HIGH tank rapidly decreased, corresponding with the rapid increase of heterotrophic nano-flagellates and virus numbers on the same day. Sediment traps were deployed at the bottom of the experimental tanks, and were periodically retrieved. These samples were observed both under light microscope and epi-fluorescent microscope with UV-excitation. It was observed that the main components of the vertical flux were amorphous suspended matter, mostly originating from dead phytoplankton and living diatoms. It was further observed from the pictures that vertical transport of oil emulsions were probably conducted after adsorption to amorphous suspended matter and living diatoms, and were settling in the sediment traps at the bottom of the tanks. This means that the main force which drives the soluble fraction of oil into bottom sediment would be vertical flux of such amorphous suspended particles and phytoplankton. Further incubation of the samples revealed that the oil emulsions were degraded by the activity of autochtonous bacteria in the sediment in aerobic condition.     

Low-temperature crystal structures of stibnite implying orbital overlap of Sb 5s2 inert pair electrons

The crystal structure of stibnite [Sb₂S₃, Pnma, a=11.314(2), b=3.837(2), c=11.234(3) Å, V= 487.7(3) ų at 293 K] was refined in situ at 230, 173, and 128 K. It is a major characteristic of the structure that the Sb–S secondary bonds enclosing Sb 5s² inert lone-pair electrons at 293 K are significantly shorter than the corresponding sum of the Sb and S van der Waals radii. Concerning the temperature dependence, although both the polyhedral volume and the cation eccentricity of the two SbS₇ polyhedra exhibit continuous contractions with decreasing temperature, the sphericity values remain constant, indicating isotropic shrinkage. Consequently, the geometries of Sb 5s² inert lone-pair electrons and ligand atoms remain unchanged at low temperatures. This is because the crystal structure of stibnite at low temperature induces contraction with attractive interactions, which is called the orbital overlap between Sb 5s² inert lone-pair electrons and ligand orbitals to maintain the coordination environment. In this case, Sb 5s² lone-pair electrons are not inert, but active. Such orbital overlaps of inert lone-electron pairs can provide a reasonable explanation for shorter secondary bonds and lower band gap energy of the binary compounds containing heavy elements such as Sb, Te, Pb, and Bi, which are key factors in tracing the origins of color, luster, and semiconductivity of their minerals or compounds.     

Long-term patterns in the diets of Japanese temperate bassLateolabrax japonicus larvae and juveniles in Chikugo estuarine nursery ground in Ariake Bay, Japan

Larval and juvenile Japanese temperate bass (Lateolabrax japonicus) samples were collected from a wide range of spatial gradients (covering a distance of approximately 30 km) in Chikugo estuary, Ariake Bay, Japan over a period of 8 yr (1997–2004) in order to observe changes in diet. Gut contents were studied by separating, identifying, counting, and estimating the dry weight of prey organisms. Copepod samples were collected during each cruise to observe the numerical composition, abundance, and biomass in the estuary. Considerable spatial and temporal variations were observed in copepod distributions in ambient water and the diets of the fish. Two distinctly different copepod assemblages were identified in the estuary: One in the upper estuarine turbidity maximum (ETM), dominated by a single speciesSinocalanus sinensis and the other in the lower estuary consisting of a multispecies assemblage, dominated byOithona davisae, Acartia omorii, Paracalanus parvus, andCalanus sinicus. The gut content composition of the fish in the upper estuary was dominated byS. sinensis, while in the lower estuary, it consisted ofP. parvus, O. davisae, andA. omorii. Within the size group analyzed (13.0–27.0 mm SL), the smaller individuals were found to feed on a mixed diet composed of smaller prey. The diets gradually shifted to bigger prey composed predominantly ofS. sinensis for larger size groups. Greater proportions of empty guts were recorded in the smaller individuals and dropped with increasing fish size. Higher dry biomass of copepods in the environment, as well as higher dry weights of gut contents, were recorded in the upper estuary, indicating that the upper estuarine ETM areas are important nursery grounds for the early life stages of the Japanese temperate bass. The early life stages of the Japanese temperate bass are adapted to use the upstream nursery grounds and ascending to the nursery areas to useS. sinensis is one of the key survival strategies of the Japanese temperate bass in the Chikugo estuary.     

Nutrient and carbon removal ratios and fluxes in the Ross Sea, Antarctica

Net community production (NCP) and nutrient deficits (Def(X)) were calculated using decreases in dissolved CO₂ and nutrient concentrations due to biological removal in the upper 200 m of the water column during four cruises in the Ross Sea, Antarctica along 76°30′S in 1996 and 1997. A comparison to excess dissolved and particulate organic carbon showed close agreement between surplus total organic carbon (TOC) and NCP during bloom initiation and productivity maximum; however, when TOC values had returned to low wintertime values NCP was still significantly above zero. This seasonal NCP, 3.9±1 mol C m⁻², must be equivalent to the particle export to depths greater than 200 m over the whole productive season. We estimate that the annual export was 55±22% of the seasonal maximum in NCP. The fraction of the seasonal maximum NCP that is exported through 200 m is significantly higher than that measured by moored sediment traps at a depth of 206 m. The removal of carbon, nitrate and phosphate (based on nutrient disappearance since early spring) and their ratios showed significant differences between regions dominated by diatoms and regions dominated by the haptophyte Phaeocystis antarctica. While the ΔC/ΔN removal ratio was similar (7.8±0.2 for diatoms and 7.2±0.1 for P. antarctica), the ΔN/ΔP and ΔC/ΔP removal ratios for diatoms (10.1±0.3 and 80.5±2.3) were significantly smaller than those of P. antarctica (18.6±0.4 and 134.0±4.7). The similarity in ΔC/ΔN removal ratios of the two assemblages suggests that preferential uptake of phosphate by diatoms caused the dramatic differences in ΔC/ΔP and ΔN/ΔP removal ratios. In contrast to low ΔC/ΔP and ΔN/ΔP removal ratio in diatom-dominated areas early in the growing season, deficit N/P and C/P ratios in late autumn indicate that the elemental stochiometry of exported organic matter did not deviate significantly from traditional Redfield ratios. Changes in biologically utilized nutrient and carbon ratios over the course of the growing season indicated either a substantial remineralization of phosphate or a decrease in phosphate removal relative to carbon and total inorganic nitrogen over the bloom period. The species dependence in C/P ratios, and the relative constancy in the C/N ratios, makes N a better proxy of biological utilization of CO₂.     

Thermal evolution of the Tseel terrane,SW Mongolia and its relation to granitoid intrusions in the Central Asian Orogenic Belt

The timing and thermal effects of granitoid intrusions into accreted sedimentary rocks are important for understanding the growth process of continental crust. In this study, the petrology and geochronology of pelitic gneisses in the Tseel area of the Tseel terrane, SW Mongolia, are examined to understand the relationship between igneous activity and metamorphism during crustal evolution in the Central Asian Orogenic Belt (CAOB). Four mineral zones are recognized on the basis of progressive changes in the mineral assemblages in the pelitic gneisses, namely: the garnet, staurolite, sillimanite and cordierite zones. The gneisses with high metamorphic grades (i.e. sillimanite and cordierite zones) occur in the central part of the Tseel area, where granitoids are abundant. To the north and south of these granitoids, the metamorphic grade shows a gradual decrease. The composition of garnet in the pelitic gneisses varies systematically across the mineral zones, from grossular‐rich garnet in the garnet zone to zoned garnet with grossular‐rich cores and pyrope‐rich rims in the staurolite zone, and pyrope‐rich garnet in the sillimanite and cordierite zones. Thermobarometric analyses of individual garnet crystals reveal two main stages of metamorphism: (i) a high‐P and low‐T stage (as recorded by garnet in the garnet zone and garnet cores in the staurolite zone) at 520–580 °C and 4.5–7 kbar in the kyanite stability field and (ii) a low‐P and high‐T stage (garnet rims in the staurolite zone and garnet in the sillimanite and cordierite zones) at 570–680 °C and 3.0–6.0 kbar in the sillimanite stability field. The earlier high‐P metamorphism resulted in the growth of kyanite in quartz veins within the staurolite and sillimanite zones. The U–Pb zircon ages of pelitic gneisses and granitoids reveal that (i) the protolith (igneous) age of the pelitic gneisses is c. 510 Ma; (ii) the low‐P and high‐T metamorphism occurred at 377 ± 30 Ma; and (iii) this metamorphic stage was coeval with granitoid intrusion at 385 ± 7 Ma. The age of the earlier low‐T and high‐P metamorphism is not clearly recorded in the zircon, but probably corresponds to small age peaks at 450–400 Ma. The low‐P and high‐T metamorphism continued for c. 100 Ma, which is longer than the active period of a single granitoid body. These findings indicate that an elevation of geotherm and a transition from high‐P and low‐T to low‐P and high‐T metamorphism occurred, associated with continuous emplacement of several granitoids, during the crustal evolution in the Devonian CAOB.     

The significance of silica precipitation on the formation of the permeable–impermeable boundary within Earth's crust

The hydrological system within Earth's crust is divided into the permeable zone and the underlying, much less permeable zone. In this study, we investigated the solubility and precipitation kinetics of silica in water under the conditions of the Kakkonda geothermal field, Japan, where well WD‐1a penetrates the boundary between the hydrothermal convection zone and the heat conduction zone. We found that quartz solubility has a local minimum at the depth of the hydrological boundary, at ~3100‐m depth (380 °C and 24 MPa), in the case of either hydrostatic conditions or fluid pressure increase above hydrostatic at deeper levels. The hydrothermal experiments reveal that rapid quartz precipitation occurs via nucleation when fluids are brought from the liquid region to the supercritical region. The preferential precipitation of quartz at a specific depth plays a significant role in forming and sustaining the permeable–impermeable boundary in the crust.     

Tracing depositional consequences of environmental radionuclides (137Cs and 210Pb) in Slovenian forest soils

Depth distribution profiles of environmental radionuclides (¹³⁷Cs and ²¹⁰Pb) have been investigated in soil to elucidate the underlying environment of semi-natural temperate deciduous and/or coniferous forest soils in Slovenia (?irovski vrh, Idrija, Ko?evski Rog, Pohorie, Gori?nica and Rakitna). Surface enrichment of both nuclides was observed at all the sites investigated in this study, suggesting that the soils had undergone little natural or anthropogenic disturbance for at least the last several decades. Apparent annual burial rates of ¹³⁷Cs (0.1–0.2 cm y^??1) were estimated to be about 1.3 times higher than those of ²¹⁰Pb at individual sites of different lithology, which suggests strong affinity of ²¹⁰Pb to soil organic matter. Variability of the vertical distribution profiles of these nuclides depends not only on “in situ” pedology but also on geographical and meteorological conditions, especially precipitation and wind direction.