Lithological,structural, and chronological relationships between the Sanbagawa Metamorphic Complex and the Cretaceous Shimanto Accretionary Complex on the central Kii Peninsula,SW Japan

It is essential to clarify the lithological, structural, and chronological relationships between the Sanbagawa Metamorphic Complex (MC) and the Cretaceous Shimanto Accretionary Complex (AC) for understanding the tectonic evolution of SW Japan. To this end, we carried out a detailed field survey of the Sanbagawa MC and the Cretaceous Shimanto AC on the central Kii Peninsula, where they are in direct contact with each other. We also conducted U–Pb dating of detrital zircons from these complexes. The field survey showed that the boundary between the Iro Complex of the Sanbagawa MC and the Mugitani Complex of the Shimanto AC, Narai Fault, shows a sinistral sense of shear with a reverse dip‐slip component, and there are significant differences in the strain intensity and the degree of recrystallization between the two complexes across this fault. Detrital zircon U–Pb dating indicates that the Iro Complex in the hanging wall of the Narai Fault shows a significantly younger maximum depositional age than the Mugitani Complex in the footwall of the fault, and an apparently large gap in the MDA of ca. 35 Myr exists across this fault. This large age gap across the Narai Fault suggests that this fault is an essential tectonic boundary fault within the Cretaceous accretionary–metamorphic complexes on the Kii Peninsula, and is considered to be an out‐of‐sequence thrust. In addition, a similar shear direction and a large age gap have been identified across the Ui Thrust, which marks the boundary between the Kouyasan and Hidakagawa belts of the Cretaceous Shimanto AC. The Cretaceous accretionary–metamorphic complexes record the large‐scale tectonic juxtapositions of complexes, and these juxtaposed structures had been caused by sinistral–reverse movements on the tectonic boundary faults such as the Narai Fault and the Ui Thrust.     

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Stable isotope-guided analysis of congener-specific PCB concentrations in a Japanese coastal food web

Organisms collected from a coastal ecosystem in Japan were analyzed for concentrations of 205 polychlorinated biphenyls (PCBs) congeners; analyses were guided by δ¹³C and δ¹⁵N measurements. The regression slopes of log PCB concentration on δ¹⁵N value are regarded as indices of biomagnification in food webs. The slope (wet weight basis) of ΣPCBs was +0.104; the slope (lipid weight basis) was close to zero. Lipid content increased from 0.06% in a primary producer to 8.32% in the highest trophic level consumer. Hence, biomagnification of ΣPCBs (wet weight basis) can be attributed to increase of lipid content through the food web. For most of the congeners, the slopes (wet weight basis) exceeded those (lipid weight basis) by ca. 0.10. Slopes increased with increasing PCB chlorination levels between chlorine numbers 1–6; slopes decreased at higher chlorination levels. This decrease is likely caused by a decrease in membrane permeability with increasing molecular weight.     

Trace element concentrations in barramundi (Lates calcarifer) collected along the coast of Vietnam

We determined concentrations of 23 trace elements (TEs), and stable carbon and nitrogen isotope (δ¹³C and δ¹⁵N) signatures in barramundi (Lates calcarifer) specimens collected along the coast of Vietnam in the Northern (NCZ), Central (CCZ) and Southern (SCZ) zones in the period 2007–2010. A combination of δ¹³C and δ¹⁵N signatures provided insight into ontogenetic shifts in barramundi foraging choices. There were clear zone-dependent differences in Mn, As, Sr and Tl concentrations; levels of Tl were highest in the NCZ, As in the CCZ, and Mn and Sr in the SCZ. Lowest concentrations of Rb occurred in the NCZ, Bi was lowest in the CCZ, and Cd and Cs were lowest in the SCZ. δ¹⁵N values significantly increased with increasing Zn, Se, Sn and Cs. Concentrations of TEs in barramundi from Vietnam were below worldwide guidelines for human consumption.     

On Structure and Temporal Variation of the Bifurcation Current off the Kii Peninsula

The Kii Bifurcation Current is often found along the southwest coast of the Kii Peninsula, and its frequency of occurrence reaches about 70% in the period from 1988 to 1996 (Takeuchi et al., 1998a). In order to clarify the structure and short-period variability of the Kii Bifurcation Current, detailed observations were made four times on board the R/V Seisui-maru of Mie University on October 29–31, 1996, on June 24–26, 1997, October 14–16, 1997, and December 3–4, 1997. The measured horizontal structure of the Kii Bifurcation Current indicates that the eastern portion of the Current (eastward flow near Cape Shionomisaki) consists of a part of the current zone of the Kuroshio. It is shown that the current structure, including the Kii Bifurcation Current in the vicinity of Cape Shionomisaki, is stable when the Kuroshio is flowing in a stationary straight path, but that the current structure is considerably changed when small-scale eddies pass by the cape. Such short-period variation can be monitored by using the daily variation of the sea level difference between Kushimoto and Uragami. In particular, in the case of October 29–31, 1996, when an eminent small-scale eddy passed by Cape Shionomisaki, and when the Kuroshio axis tentatively moved southwards about 50 km apart from the coast, the Kii Bifurcation Current seems to have disappeared.     

Differences in the acute toxicities of tributyltin between the Caprellidea and the Gammaridea (Crustacea: Amphipoda)

Tests for the acute toxicity of tributyltin (TBT) were conducted on amphipod crustaceans collected from Otsuchi Bay, Japan. Five species of caprellids and three species of gammarids, which belong to a closely related ecological niche, were used for the exposure experiments at seven test concentrations (0, 0.001, 0.01, 0.1, 1, 10 and 100 microg TBTCl/l) for 48 h at 20 degrees C. The 48-h LC50 values of the caprellids were 1.2-6.6 microg TBTCl/l, and these were significantly lower than those of the gammarids (17.8-23.1 microg TBTCl/l). This suggests that caprellids are more sensitive to TBT than gammarids. Furthermore, the proportions of TBT and its derivatives, dibutyltin (DBT) and monobutyltin (MBT), were measured in the amphipods collected from Otsuchi Bay. In the caprellids, TBT was the predominant compound, accounting for 72% of the total butyltin which reflected the butyltin ratio in seawater, while in the gammarids, TBT's breakdown products (DBT and MBT) predominated, accounting for 75% of the total butyltin. This difference suggests that caprellids may have lower metabolic capacity to degrade TBT than gammarids. Therefore, the difference in sensitivity to TBT among the amphipods is thought to be related to the species-specific capacity to metabolize TBT.     

Bioconcentration and biomagnification of polybrominated diphenyl ethers (PBDEs) through lower-trophic-level coastal marine food web

Bivalves, crabs, fishes, seawater, and sediment collected from the inner part of Tokyo Bay, Japan, were measured for 20 polybrominated diphenyl ether (PBDE) and 5 polychlorinated biphenyl (PCB) congeners. To determine the trophic levels of the organisms, carbon and nitrogen stable isotope ratios (δ¹³C and δ¹⁵N) were also measured. Bioconcentration factors of PBDE and PCB congeners increased as the octanol-water partition coefficient (K_ow) rose to log K_ow = 7, above which they decreased again. Biomagnification of PCBs and several PBDE congeners (BDE47, 99, 100, 153 and 154) up the trophic ladder was confirmed by a positive correlation between their concentrations and δ¹⁵N. Other PBDE congeners showed a negative or no correlation, suggesting their biotransformation through metabolism. The more hydrophobic congeners of both PBDEs (Br = 2-6) and PCBs (Cl = 6-9) were biomagnified more. It thus appears that PBDEs are less biomagnified than PCBs.