Vertical distribution of smaller macrobenthos and larger meiobenthos in the sediment profile in the deep-sea system of Suruga Bay (central Japan)

The vertical distribution of benthic organisms in the sediment profile was studied using horizontally sliced sediments collected at five stations at depths from 115 to 472 m in Suruga Bay, central Japan. Using sieves of 1.0 and 0.5 mm mesh, benthic organisms were divided into two size classes, smaller macrobenthos (>1mm, <1g wet weight) and larger meiobenthos (1.0 mm0.5 mm). The maximum depth of vertical distribution of organisms in the sediment profile was expressed by the 95 % intercept of the cumulative % curve of the number of individuals drawn with respect to depth in the sediment. It has long been supposed that benthic animals are concentrated in the surface centimeters of sediment in the deep-sea system, and the present study clearly substantiated this. Most benthic organisms of both of these two size classes were concentrated in the upper 5 cm of sediment. The vertical distribution was almost always deeper in the case of smaller macrobenthos than for larger meiobenthos. However the difference could not be substantiated statistically since the number of samples was insufficient. The maximum depth indices of polychaetes were found to be significantly larger than those of crustaceans in the case of macrobenthos, while in the case of meiobenthos, the difference was not significant. The maximum depth index of all benthic organisms was positively and significantly correlated with water-depth and the possible cause for this relationship is discussed.     

Quantitative studies on the smaller macrobenthos inhabiting various topographical environments around the Sagami bank in the deep-sea system of Sagami Bay

A survey was made in an area of complicated topography within the deep-sea system of Sagami Bay. Samples were obtained quantitatively with the Smith-McIntyre bottom-sampler of 1/10 m² and were washed through a screen of 1.0 mm mesh. The biomass, the number of individuals and the number of species were studied at each station in relationship to submarine topography. All the items showed more or less parallel features in three topographical environments. High figures were found on the top of the bank and low ones in the canyon, while those values obtained in the sloping environment were intermediate and variable. The percent composition of the quantitatively important animal groups was rather constant throughout the top of the bank, and in this hahitat the faunal diversity was higher than in the others. From the distributional patterns of the species, and also from the species composition and dominancy at each station, the benthic communities of the bank-top and of the canyon were known to be distinct. In the sloping environment, however, the benthic assemblages at some stations were related to the bank-top community, either being its impoverished phase or with several elements peculiar to the slope, while at the remaining stations they were rather peculiar but related to the canyon community. All the aspects of the benthic ecology mentioned above were found to be closely related, both in their general and special features, to the nature of the sediments, in which three major types were recognized corresponding to the above three topographical environments. From the nature of the sediment, water movement, if any, can be expected on the top of the bank, and this is reflected in the preponderance of plankton- and/or ceston feeders making up this benthic community. Within the canyon, there were found the impoverishment of benthic community which is supposed to be due to the stagnant environment. The biomasses of the whole area were compared to those in other regions in the form of cumulative curves. In the deep-sea system of Sagami Bay which is well surrounded by land, the biomasses were only slightly lower than those of the shallow-sea system on the shelves in neighbouring regions, and those of a shallow enclosed bay were an order of magnitude higher than these figures. Those in the offshore parts of the continental shelf, remote from the coast, were nearly an order of magnitude lower. This work is carried out as a part of JIBP-PM Project     

Volcanic activity related to the formation of the Kuroko-type deposits in the Kosaka district,Japan

In the Miocene Kosaka formation of NE-Japan, submarine volcanic sedimentary deposits of the Kuroko-type occur. This formation consists mainly of volcanics which erupted in a submarine environment. The Kosaka Volcano was built up by nine or more volcanic events of a single eruptive cycle. The mode of eruption during a representative single eruptive cycle changed as follows: The Uwamuki tuff breccia is a contact product between dacitic magma and the sea water. Dacitic magma pushed the Motoyama dacite dome upward, as a result of the decrease in vesicularity and perhaps also in temperature. Next, a steam explosion occurred at a flank of this lava dome. The hydrothermal activity which began in this steam explosion center is responsible for the formation of the Kuroko-type Cu-Zn-Pb-mineral deposits. Similar examples of a single eruptive cycle as at Kosaka are also found in Quaternary terrestrial volcanoes of Japan.

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Zusammenfassung Submarin-vulkanisch-sedimentäre Lagerstätten des Kuroko-Typs kommen in der miozänen Kosaka-Formation vor, wo im letzten Jahrhundert der Name Kuroko zuerst angewandt wurde. Diese Formation besteht hauptsächlich aus submarinen Vulkaniten. Der Kosaka-Vulkan wurde in mindestens neun Ausbruchzyklen aufgebaut. Die Art der Eruption änderte sich während eines typischen Einzelausbruchs folgendermaßen: Die Uwamuki Tuff-Brekzie entstand durch Kontaktwirkung zwischen dazitischem Magma und Seewasser. Eine Abnahme des Gasgehaltes und vielleicht auch der Temperatur führten zur oberflächennahen Intrusion des Motoyama Dazitdoms. An einer Flanke dieses Lavadoms kam es zur Dampfexplosion. Die Hydrothermaltätigkeit, die in diesem Dampfexplosionszentrum begann, ist verantwortlich für die Bildung der Minerallagerstätten vom Kuroko-Typ. Ähnliche Beispiele eines Ausbruchszyklus vom Kosaka-Typ wurden ebenfalls in quartären terrestrischen Vulkanen in Japan gefunden, wobei hier keine Minerallagerstätten des Kuroko-Typs vorkommen.

     

Culture-dependent and independent analyses of subsurface microbial communities in oil-bearing strata of the Sagara oil reservoir

Abstract   Culture-dependent and independent methods were used to evaluate the microbial communities in cores collected at depths up to 200 m in oil-bearing and oil-free strata near the Sagara oil reservoir near Shizuoka, Japan. Direct microbial counts revealed much higher numbers (2.2 × 10⁴−7.9 × 10⁶/g) of microbes in the oil-bearing strata than in the oil-free zones, where counts were uniform at approximately 1.0 × 10⁴/g. Molecular taxonomic analyses via 16S rRNA gene sequence comparisons showed that the oil-free strata were dominated by members of the γ-Proteobacteria including Pseudomonas , Stenotrophomonas and Sphingomonas , whereas the oil-bearing strata were dominated by a single species closely related to Pseudomonas stutzeri . All archaeal clones were phylogenetically affiliated with the uncultured soil group in Crenarchaeota with the exception of a single phylotype that belonged to the genus Thermococcus . Culture-dependent analysis was carried out by most-probable-number culturing as well as direct plating to determine viable cell counts, using both complex organic substrates or native oil and autotrophic media. Both culture-dependent and independent methods revealed the abundant cultivable member was the aerobic oil-degrading bacterium Pseudomonas stutzeri and neither autotrophs nor anaerobic heterotrophs could be detected in the oil-bearing strata.     

Opening of the Sea of Japan and Kuroko deposit formation

The opening of the Sea of Japan began with the bulge at the margin of the Asian continent at 21 Ma. Crustal subsidence and basaltic eruption prior to Kuroko deposit formation appear to represent the opening event. Between 16.5 to 15.5 Ma was the most probable time of the counterclockwise rotation of NE Japan. Kuroko ore formation is believed to have taken place between 15.4 and 15.2 Ma based on geological evidence and fossil ages. It is proposed that Kuroko deposits formed in a weakly extensional environment at the waning stage of opening of the Sea of Japan. This may be the only model which can account for the occurrence and simultaneous formation of Kuroko deposits in Japan. The process can be ascribed to decreasing porosity of the crust due to the stress change, most commonly from extensional to compressional.     

Comparative Performance of Steel Drainage Pipes Against Flood-Induced Deformation in River Levee

Geotechnical and Geological Engineering - Steel drainage pipes that can provide both drainage and reinforcement functions are expected to give better performance in levee protection against...     

A new mothed of classifying the growth form of corals and its application to a field survey of coral-associated animals in Kabira Cove,Ishigaki Island

In order to classify the growth form of corals, the following “growth form index” was defined to denote coral shape objectively: Growth Form Index=Coral Surface Area/ (Coral Wet Weight)^2/3. On the basis of this index, growth forms of corals were classified into four major forms: massive, irregular shaped, branching, and highly branching. Coral-associated animals were classified into four groups according to their mode of living: freeliving epi-, sessile epi-, boring crypto-, and secondary crypto-bionts. For the quantitative study of the distribution of coral-associated animals in each growth form of coral and in each habitat of the study area, living coral heads were collected using SCUBA from 10 stations representing various habitats in Kabira Cove, Ishigaki Island, Yaéyama Group, Okinawa Prefecture. By comparing the proportions of four life forms of animals associated with each of the four different growth forms of corals at each station, some consistent patterns were found: massive corals were dominated by both boring and secondary cryptobionts, while branching and highly branching corals were dominated by free-living and sessile epibionts. In addition, the absolute numbers as well as the proportions of the four life forms of animals associated with a given growth form of coral changed from the outer-reef outside the bay to the bay head. From these various distribution patterns, it became clear that the growth forms of corals have a strong influence on the micro ecological distribution of coral-associated animals at each station, while the physical environment regulates the distribution of these animals in a given locality on the macroscopic scale.