Gas hydrate saturation at Site C0002, IODP Expeditions 314 and 315, in the Kumano Basin,Nankai trough

The degree of gas hydrate saturation at Integrated Ocean Drilling Program (IODP) Site C0002 in the Kumano Basin, Nankai Trough, was estimated from logging‐while‐drilling logs and core samples obtained during IODP Expeditions 314 and 315. Sediment porosity data necessary for the calculation of saturation were obtained from both core samples and density logs. Two forms of the Archie equation (‘quick‐look’ and ‘standard’) were used to calculate gas hydrate saturation from two types of electrical resistivity log data (ring resistivity and bit resistivity), and a three‐phase Biot‐type equation was used to calculate gas hydrate saturation from P‐wave velocity log data. The gas hydrate saturation baseline calculated from both resistivity logs ranges from 0% to 35%, and that calculated from the P‐wave velocity log ranges from 0% to 30%. High levels of gas hydrate saturation (>60%) are present as spikes in the ring resistivity log and correspond to the presence of gas hydrate concentrations within sandy layers. At several depths, saturation values obtained from P‐wave velocity data are lower than those obtained from bit resistivity data; this discrepancy is related to the presence of free gas at these depths. Previous research has suggested that gas from deep levels in the Kumano Basin has migrated up‐dip towards the southern and seaward edge of the basin near Site C0002. The high saturation values and presence of free gas at site C0002 suggest that a large gas flux is flowing to the southern and seaward edge of the basin from a deeper and/or more landward part of the Kumano Basin, with the southern edge of the Kumano Basin (the location of site C0002) being the main area of fluid accumulation.     

Structurally preserved Zamites bayeri Kvaček from the Coniacian Kashima Formation (Yezo Group) of Hokkaido,Japan

A permineralized frond from the Coniacian Kashima Formation (Yezo Group) of Hokkaido, Japan, is identified as Zamites bayeri based on leaf shape, transverse orientation of stomata, papillate epidermal surface, and hollow subsurface bodies formed only on the abaxial epidermis. The specimen has an articulation at the base of the leaflet from which the leaflet was detached by means of an abscission zone. This finding suggests that Z. bayeri has compound leaves that are functionally equivalent to a twig bearing simple leaves. This functional conversion is often found in extant compound-leaved ferns or cycads growing in infertile conditions; thus Z. bayeri might have lived in a similar habitat. Leaflet articulation is also found in other Zamites species including the type species of the genus, whereas it is unknown in other bennettitalean foliar morphogenera. The rachis of the specimen has a columnar vascular bundle, which is common in bennettitalean foliage.     

Seismic velocity structure around the Hyuganada region, Southwest Japan, derived from seismic tomography using land and OBS data and its implications for interplate coupling and vertical crustal uplift

The Hyuganada region, a forearc region of Southwest Japan, is characterized by several interesting geological and geophysical features, i.e., significant aseismic crustal uplift of 120 m during the past 120 thousand years at the Miyazaki Plain, negative free-air gravity anomalies with the maximum magnitude of −130 mgal, and relatively less cohesive interplate coupling compared with that for off the Shikoku and Kii Peninsula. In order to examine the causes of these observations, we determined a detailed three-dimensional seismic velocity structure based on the seismic data observed by ocean bottom seismometers (OBS) and land stations. P- and S-wave tomographic velocity structures clearly indicate the subducting slab and also the zones of high Poisson's ratio at 25–35 km depth along the coastline of the northeastern part of the Hyuganada. The region with high Poisson's ratio may correspond to the serpentinized mantle wedge as suggested for other mantle wedges, and appears to be coincident with the zone for observed aseismic slips such as the slow-slip and after-slip events. Also, the detection may be related to a relatively weak interplate coupling in the Hyuganada region. The tomographic structures also indicate low velocity zones with a horizontal scale comparable to the Kyushu-Palau Ridge in and around the subducting slab. If we assume that the low velocity zones correspond to the subducted Kyushu-Palau Ridge, then the predicted gravity anomaly due to the density contrast between the low velocity zones and the surrounding region can explain about 60% of the gravity anomaly in the Hyuganada region. The buoyancy is probably an important factor for the crustal uplift observed in the Miyazaki Plain, the steep bending of the subducting slab and the normal fault-type earthquakes around the Hyuganada region.     

A Challenge of Water Purification in Dokai Bay, Japan

A history of water pollution and countermeasures for water purification in Dokai Bay, Japan are reviewed. Now, Dokai Bay suffers from the occurrences of red tides and oxygen-deficiency in summer. In order to prevent the occurrences of red tides and oxygen-deficiency, an ecological numerical model has been developed. The model experiments forecast that when the phosphorus or nitrogen load from land will be cut by 90% or 95%, respectively, red tides and oxygen-deficiency will not occur in Dokai Bay. If the industrial and sewage facilities are not sufficient to cut the nutrients load to the necessary degree, we have to consider other countermeasures such as cultivating bivalves and algae in order to decrease the nutrients concentration in the bay. International co-operation related to coastal zone management is also discussed.     

Colonization of Sulfurovum sp. on the gill surfaces of Alvinocaris longirostris, a deep-sea hydrothermal vent shrimp

Deep‐sea hydrothermal vents are unique light‐independent ecosystems that are sustained by chemosynthetic bacteria. For many of the invertebrates inhabiting in such environments, bacteria play essential roles in both energy acquisition and detoxification of potentially toxic gases such as H₂S. In this study, the bacterial flora present on the gills of Alvinocaris longirostris (Bresiliidae: Caridea), a shrimp inhabiting hydrothermal vents (1532 m depth) at the Hatoma Knoll of the Okinawa Trough, was investigated. Bacterial 16S rDNA fragments were successfully amplified from the gills and 70% of these fragments showed an identical pattern in the restriction fragment length polymorphism analysis. These fragments were assigned to the ribotype AL‐1. Phylogenetic analyses suggest that AL‐1 forms a monophyletic clade with Sulfurovum spp. (ε‐Proteobacteria). Fluorescence in situ hybridization for AL‐1 and electron microscopy showed the presence of short‐rod bacteria lining up on the cuticular layer of the surface of the gill filaments. These results suggest that bacterial association with gills also occurs in bresiliid shrimps.     

Isotope dilution sector-field inductively coupled plasma mass spectrometry combined with extraction chromatography for rapid determination of 241Am in marine sediment samples: A case study in Sagami Bay, Japan

²⁴¹Am is a useful tracer for understanding biogeochemical processes in the marine environment. ²⁴¹Am also poses a potential radiation threat to human health due to the continuous increase of its concentration in the global environment. We report a rapid analytical method for determining ²⁴¹Am in marine sediments using isotope dilution sector-field inductively coupled plasma mass spectrometry (SF-ICP-MS) combined with a high-efficiency sample introduction system (APEX-Q). A selective CaF₂ co-precipitation procedure followed by TRU extraction chromatography was employed to effectively remove the major sediment matrix and to pre-concentrate ²⁴¹Am. We achieved an extremely low detection limit of 0.32 fg/g or 0.041 mBq/g (for 1 gram sediment), which is better than that of alpha spectrometry, and it allowed the accurate determination of ²⁴¹Am in low-level marine sediment samples. The accuracy and precision of the developed analytical method was evaluated using a laboratory prepared Am isotope standard solution and Ocean Sediment reference material (IAEA-368). The results were satisfactory. For sediment samples, overall chemical recoveries varied from 60–90%. The developed method was applied to the study of ²⁴¹Am depth distribution in Sagami Bay, Japan, where we observed different depth profiles between ²⁴¹Am activity and ^239+240Pu activity.     

Improving the prospects for detecting extrasolar planets in gravitational microlensing events in 2002

Gravitational microlensing events of high magnification have been shown to be promising targets for detecting extrasolar planets. However, only a few events of high magnification have been found using conventional survey techniques. Here we demonstrate that high-magnification events can be readily found in microlensing surveys using a strategy that combines high-frequency sampling of target fields with on-line difference imaging analysis. We present 10 microlensing events with peak magnifications greater than 40 that were detected in real-time towards the Galactic bulge during 2001 by the Microlensing Observations in Astrophysics (MOA) project. We show that Earth-mass planets can be detected in future events such as these through intensive follow-up observations around the event peaks. We report this result with urgency as a similar number of such events are expected in 2002.     

P–V–T equation of state of Mn3Al2Si3O12 spessartine garnet

The thermoelastic parameters of synthetic Mn₃Al₂Si₃O₁₂ spessartine garnet were examined in situ at high pressure up to 13 GPa and high temperature up to 1,100 K, by synchrotron radiation energy dispersive X-ray diffraction within a DIA-type multi-anvil press apparatus. The analysis of room temperature data yielded K ₀ = 172 ± 4 GPa and K ₀ ^′  = 5.0 ± 0.9 when V _0,300 is fixed to 1,564.96 Å³. Fitting of P–V–T data by means of the high-temperature third-order Birch–Murnaghan EoS gives the thermoelastic parameters: K ₀ = 171 ± 4 GPa, K ₀ ^′  = 5.3 ± 0.8, (?K _0,T /?T) _P  = ?0.049 ± 0.007 GPa K^?1, a ₀ = 1.59 ± 0.33 × 10^?5 K^?1 and b ₀ = 2.91 ± 0.69 × 10^?8 K^?2 (e.g., α _0,300 = 2.46 ± 0.54 × 10^?5 K^?1). Comparison with thermoelastic properties of other garnet end-members indicated that the compression mechanism of spessartine might be the same as almandine and pyrope but differs from that of grossular. On the other hand, at high temperature, spessartine softens substantially faster than pyrope and grossular. Such softening, which is also reported for almandine, emphasize the importance of the cation in the dodecahedral site on the thermoelastic properties of aluminosilicate garnet.     

Movement of radiocaesium fallout released by the 2011 Fukushima nuclear accident

The moment magnitude (M _w) 9.0 Tohoku-Oki Earthquake occurred on March 11, 2011, generating an unusually large tsunami. The seismic shocks and tsunami inundation severely damaged the Fukushima Daiichi Nuclear Power Plant. Radionuclide emission due to reactor breakdown contaminated wide areas of Fukushima and its surroundings. Heavy rainfall causes runoff across surface soil, and fine soil particles are susceptible to uptake by the flowing water. The high radioactivity of grains suspended in floodwater indicates that radioactive fallout was streamed into rivers in particulate form and transported downstream under high-flow conditions. Here, we investigated the diachronic mode of ¹³⁴Cs and ¹³⁷Cs in central Fukushima, through which the contaminated air mass drifted and caused wet deposition of radionuclides. Stratigraphic measurements of radioactivity in sediment cores is the method employed in this study to determine the basin-wide movement of ¹³⁴Cs and ¹³⁷Cs, to evaluate the significance of the erosion–transportation–accumulation processes on natural decontamination in terrain characterized by steep slopes and high precipitation. Stratigraphic results illustrate the process of fluvial sediment discharge, and the massive deposition of radiocaesium suggests basin-wide movement of fallout during concentrated rainfall. Grain suspension in torrential currents is an important pathway for transportation of radionuclides from land to sea, and the appearance of hotspots on floodplains and the offshore sea floor is the consequence of erosion and transportation under seasonal heavy precipitation. Radioactive horizons occur in offshore sediment columns and thus radiocaesium discharged from the estuary will persist forever under the sea floor if no artificial disturbance occurs.     

Occurrence of hydroxylated polychlorinated biphenyls in the brain of cetaceans stranded along the Japanese coast

Levels of hydroxylated polychlorinated biphenyls (OH-PCBs) and PCBs were measured in the brain of melon-headed whales (MW: Peponocephala electra), striped dolphins (SD: Stenella coeruleoalba) and finless porpoises (FP: Neophocaena phocaenoides) stranded along the Japanese coast during 2002-2003. Levels of OH-PCBs (including identified and unknown OH-P(5)CB, -H(6)CB, -H(7)CB and O(8)CB congeners) in the brain of MW, SD and FP were in the range of 20-290, 21-330 and 170-240pg/g wet wt., respectively. Observed OH-PCB levels were 2-3 orders of magnitude lower than PCBs in the same individuals. OH-PCBs/PCBs ratios in MW, SD and FP brain were lower than those in blood of humans and wildlife and in the brain of polar bears reported previously. OH-PCBs were also detected in maternal and fetal brain of SD (1 pair), suggesting transfer of OH-PCBs into the fetal brain of odontocete cetaceans. When fetus/dam concentration ratios of OH-PCB congeners detected in maternal and fetal brain were estimated, the values were higher than those of PCB congeners, implying that OH-PCBs in maternal blood could be more easily transferred into fetal brain via placenta than PCBs.