Geochemical constraints on the depositional environment of the 1.84 Ga Embury Lake Formation,Flin Flon Belt,Canada     

Kento Motomura  Shoichi Kiyokawa  Minoru Ikehara  Kentaro Tanaka  Yuji Sano 《Island Arc》2020,29(1)

The Flin Flon Belt of Canada contains Paleoproterozoic volcanic–sedimentary sequences that are related to the Trans‐Hudson Orogeny. The sequences include island arc volcanic and volcaniclastic rocks (Amisk Group) that are unconformably overlain by subaerial sedimentary rocks (Missi Group), and younger deep facies sediments. In the Flin Flon area, several north–south trending faults divide the sequences into blocks and obscure the depositional environment of the deep facies sediments. Locally, within the Flin Flon area, the Embury Lake Formation is in fault contact with island arc volcanic–sedimentary sequences of the Amisk and Missi Groups. To identify the depositional environment of the Embury Lake Formation, we used lithologic and geochemical approaches. Here, we report carbon isotopic values in organic matter (δ¹³C_org) and sulfur isotopes (δ³⁴S), as well as total organic carbon and total sulfur measurements for the black shale in the formation. Samples were taken from a drill core that contains alternating bands of sandstone and black shale. Pyrite in the black shale is divided into four textural types: euhedral, vein‐type, elliptical, and microcrystalline. Microcrystalline pyrite is typically generated by microbially mediated sulfate reduction. An extremely low S/C ratio (avg. = 0.04) is consistent with lacustrine deposition. The ranges of δ¹³C_org (?36 ‰ to ?27 ‰) and δ³⁴S (+3.0 ‰ to +7.7 ‰) values can be explained by bacterial photosynthesis that involved Calvin cycle and acetyl CoA pathways, and sulfate reduction in a low‐sulfate environment. Considering the depositional age reported in a previous study of < 1.84 Ga, the Embury Lake Formation was likely emplaced in a lacustrine setting during the Trans‐Hudson Orogeny.  相似文献   

Contribution of different functional groups to the diet of major predatory fishes at a seagrass meadow in northeastern Japan     

Katsumasa Yamada  Masakazu Hori  Yoshiyuki Tanaka  Natsuki Hasegawa  Masahiro Nakaoka 《Estuarine, Coastal and Shelf Science》2010

We examined the variation in habitat use and diet of three dominant fish species (Myoxocephalus brandti, Pholidapus dybowskii, and Pholis crassispina) in a seagrass meadow in the Akkeshi-ko estuary in northeastern Japan, where broad and dense Zostera marina beds exist, using a semi-quantitative census of the fishes and analyses of their stomach contents. Differences among the three fish species in the temporal variation in abundance of each age class (mainly 1- and 2-year age classes) indicated that the temporal pattern of utilization of the seagrass meadow were different among them. In the semi-quantitative dietary analysis, two prey categories, i.e., taxonomic group (order and suborder) and functional group, were used to explain the variation in prey composition with size-dependent changes. The six prey functional groups were classified based on the ecological traits of the prey, i.e., trophic level, size, and life type (habitat and behavior). Ontogenetic shifts in prey of the three fish species could be fully explained by a combination of the two prey categories, and not by the use of only one category (taxonomic or functional group). The pattern of ontogenetic shifts in prey differed among the fish species and size (age) classes. These results indicate that segregation of habitat (seagrass meadow) and prey group (taxonomic and functional group) is performed among the three species, which may contribute to their coexistence in this estuary.  相似文献   

Alternating zonal flows in a two-layer wind-driven ocean     

Yuusuke Tanaka  Kazunori Akitomo 《Journal of Oceanography》2010,66(4):475-487

Alternating zonal flows in an idealized wind-driven double-gyre ocean circulation have been investigated using a two-layer shallow-water eddy-permitting numerical model. While the alternating zonal flows are found almost everywhere in the time-mean zonal velocity field, their meridional scales differ from region to region. In the subpolar western boundary region, where the energetic eddy activity induces quasi two-dimensional turbulence, the alternating zonal flows are generated by the inverse energy cascade and its arrest by Rossby waves, and the meridional scale of the flows corresponds well to the Rhines scale. In the eastern part of the basin, where barotropic basin modes are dominant, the zonal structure is formed through the nonlinear effect of the basin modes and is wider than the Rhines scale. Both effects are likely to form zonal structure between the two regions. These results show that Rossby basin modes become an important factor in the formation of alternating zonal flows in a closed basin in addition to the arrest of the inverse energy cascade by Rossby waves. The wind-driven general circulation associated with eddy activities plays an essential role in determining which mechanism of the alternating zonal flows is possible in each region.  相似文献   

Horizontal distribution and population dynamics of the dominant mysid Hyperacanthomysis longirostris along a temperate macrotidal estuary (Chikugo River estuary, Japan)     

Keita W. Suzuki  Kouji Nakayama  Masaru Tanaka 《Estuarine, Coastal and Shelf Science》2009,83(4):516-528

The estuarine turbidity maximum (ETM) that develops in the lower salinity areas of macrotidal estuaries has been considered as an important nursery for many fish species. Mysids are one of the dominant organisms in the ETM, serving as a key food source for juvenile fish. To investigate the horizontal distribution and population dynamics of dominant mysids in relation to the fluctuation of physical conditions (temperature, salinity, turbidity, and freshwater discharge), we conducted monthly sampling (hauls of a ring net in the surface water) along the macrotidal Chikugo River estuary in Japan from May 2005 to December 2006. Hyperacanthomysis longirostris was the dominant mysid in the estuary, usually showing peaks of density and biomass in or close to the ETM (salinity 1–10). In addition, intra-specific differences (life-cycle stage, sex, and size) in horizontal distribution were found along the estuary. Larger males and females, particularly gravid females, were distributed upstream from the center of distribution where juveniles were overwhelmingly dominant. Juveniles increased in size toward the sea in marked contrast with males and females. The findings suggest a possible system of population maintenance within the estuary; gravid females release juveniles in the upper estuary, juveniles grow during downstream transport, young males and females mature during the upstream migration. Density and biomass were primarily controlled by seasonal changes of temperature, being high at intermediate temperatures (ca. 15–25 °C in late spring and fall) and being low at the extreme temperatures (ca. 10 °C in midwinter and 30 °C in midsummer). High density (up to 666 ind. m⁻³) and biomass (up to 168 mg dry weight m⁻³) of H. longirostris were considered to be comparable with those of copepods in the estuary.  相似文献   

Novel sledge net system employing propulsion vehicles for sampling demersal organisms on sandy bottoms     

Hiroyuki Munehara  Yoshiki Tanaka  Tomoyuki Futamura 《Estuarine, Coastal and Shelf Science》2009

A new sledge net system using propulsion vehicles has been developed to sample more efficiently the demersal juveniles of marine organisms. A net attached to a sledge maneuvered by a SCUBA diver who uses operating switches on a steering handle to adjust the altitude of the sledge and the position of the tickler chains to ensure that the footcloth of the mouth of the net remains in constant contact with the bottom surface. Video camera, flow meter, compass, and dive computers are positioned on the sledge net in the view of the diver. Given that the system can attain speeds of 70 cm s⁻¹, the net can be employed to capture highly mobile fish. Unlike most boat-based net sampling methods, the use of propulsion vehicles means that there are no sound or vibration disturbances due to the boat and tow ropes typically used to maneuver these types of sampling nets. Marine fauna was collected at monthly intervals over a two-year period in a sampling area along the southern coast of Hokkaido, Japan. A total of 2641 specimens comprising 61 species and including five species which were the first records for the region were collected. These findings suggest that the new sledge net system employing propulsion vehicles was effective for sampling demersal juveniles, particularly in situations where sledge nets towed by boats or push nets cannot be deployed.  相似文献   

Distribution of Changjiang Diluted Water detected by satellite chlorophyll-a and its interannual variation during 1998–2007     

Hyun-Cheol Kim  Hisashi Yamaguchi  Sinjae Yoo  Jianrong Zhu  Kazumaro Okamura  Yoko Kiyomoto  Katsuhisa Tanaka  Sang-Woo Kim  Taewook Park  Im Sang Oh  Joji Ishizaka 《Journal of Oceanography》2009,65(1):129-135

Sea-viewing Wide Field-of-view Sensor (SeaWiFS) chlorophyll-a distribution in summer in the East China Sea during 1998–2007 was analyzed. Statistical analysis with K-means clustering technique allowed us to define the proper satellite chlorophyll-a concentration indicating the Changjiang Diluted Water (CDW). The spatial distributions of the higher satellite chlorophyll-a concentrations (>0.48 mg m⁻³) corresponded well with the distributions of lower salinity CDW (<30–32) every year. Interannual variation of the CDW area, indicated by the high satellite chlorophyll-a, correlated with the interannual variation of the Changjiang summer freshwater discharge. The correlation analysis indicated that the CDW spread eastward in the East China Sea with a time lag of 1 to 2 months after the discharge.  相似文献   

Vegetation history after the late period of the Last Glacial Age based on phytolith records in Nangodani Valley basin,southern part of the Aso caldera,Japan     

Yasuo Miyabuchi  Shinji Sugiyama 《第四纪科学杂志》2020,35(1-2):304-315

Vegetation history after the late period of the Last Glacial Age has been reconstructed using phytolith records obtained from three tephra sections in the Nangodani Valley basin, southern part of the Aso caldera, south-west Japan. The topography of the Nangodani Valley basin is divided into three types: somma (caldera rim and wall), caldera floor (central valley) and post-caldera central cone slope. The vegetation transitions after the late period of the Last Glacial Age in the basin vary between these topographic types. The differences can be explained based on human activities in the valley basin. Grassland dominated by Sasa and Pleioblastus dwarf bamboos (before 8 ka) and Miscanthus and other Andropogoneae pampas grasses (after 8 ka) occurred in the central valley and on the post-caldera central cone slope, which were strongly affected by human activities including a long period of burning. In contrast, forest with an understory of Bambusoideae plants was preserved on the caldera rim and wall, which was inaccessible because of its steep topography, during the Holocene.  相似文献   

Throughfall partitioning by trees     

Delphis F. Levia  Kazuki Nanko  Hiromasa Amasaki  Thomas W. Giambelluca  Norifumi Hotta  Shin'ichi Iida  Ryan G. Mudd  Michael A. Nullet  Naoki Sakai  Yoshinori Shinohara  Xinchao Sun  Masakazu Suzuki  Nobuaki Tanaka  Chatchai Tantasirin  Kozo Yamada 《水文研究》2019,33(12):1698-1708

Although we know that rainfall interception (the rain caught, stored, and evaporated from aboveground vegetative surfaces and ground litter) is affected by rain and throughfall drop size, what was unknown until now is the relative proportion of each throughfall type (free throughfall, splash throughfall, canopy drip) beneath coniferous and broadleaved trees. Based on a multinational data set of >120 million throughfall drops, we found that the type, number, and volume of throughfall drops are different between coniferous and broadleaved tree species, leaf states, and timing within rain events. Compared with leafed broadleaved trees, conifers had a lower percentage of canopy drip (51% vs. 69% with respect to total throughfall volume) and slightly smaller diameter splash throughfall and canopy drip. Canopy drip from leafless broadleaved trees consisted of fewer and smaller diameter drops (D_{50_DR}, 50th cumulative drop volume percentile for canopy drip, of 2.24 mm) than leafed broadleaved trees (D_{50_DR} of 4.32 mm). Canopy drip was much larger in diameter under woody drip points (D_{50_DR} of 5.92 mm) than leafed broadleaved trees. Based on throughfall volume, the percentage of canopy drip was significantly different between conifers, leafed broadleaved trees, leafless broadleaved trees, and woody surface drip points (p ranged from <0.001 to 0.005). These findings are partly attributable to differences in canopy structure and plant surface characteristics between plant functional types and canopy state (leaf, leafless), among other factors. Hence, our results demonstrating the importance of drop‐size‐dependent partitioning between coniferous and broadleaved tree species could be useful to those requiring more detailed information on throughfall fluxes to the forest floor.  相似文献   

A Late Holocene geomagnetic secular variation record from Erhai Lake, southwest China   总被引：1，自引：0，他引：1  

Masayuki Hyodo  Arata Yoshihara  Kenji Kashiwaya  Takashi Okimura  Toshiyuki Masuzawa  Ryotaro Nomura  Shingo Tanaka  Tang Bang Xing  Liu Su Qing  & Liu Shi Jian 《Geophysical Journal International》1999,136(3):784-790

A secular variation record of the geomagnetic field direction for the last 6.5  kyr has been obtained from the magnetization of sediment cores from Erhai Lake, southwest China. In order to make a comparison with this record, secular variation in east-central China was investigated by combining available magnetic field data from historical records and archaeomagnetic measurements since about 350 bc . The secular variation in Erhai Lake shows features consistent with the combined record, except for the oldest three observed declination swings in Sian from 720 to 900 ad . Many features of declination and inclination in China also occur in Japan. From 500 to 1000 ad , declination was westerly ranging from about −20° to −5° in Erhai Lake, east-central China, and Japan.  相似文献   

Determination of the freshwater origin of Coastal Oyashio Water using humic-like fluorescence in dissolved organic matter     

Yu Mizuno  Jun Nishioka  Takahiro Tanaka  Yuya Tada  Koji Suzuki  Yuta Tsuzuki  Atsuko Sugimoto  Youhei Yamashita 《Journal of Oceanography》2018,74(5):509-521

Coastal Oyashio Water (COW), defined as a water mass with a temperature lower than 2 °C and a salinity lower than 33.0, is distributed in the North Pacific Ocean off southeastern Hokkaido, Japan, from winter to spring. COW is rich in macronutrients and dissolved iron and is thus considered to affect the spring phytoplankton blooms in the Oyashio region. Although river water and sea-ice melt water have been considered freshwater end-members of COW, the contributions of these freshwater sources to COW have not been well described. In this study, the humic-like components in dissolved organic matter were first applied as a parameter to evaluate the freshwater end-members of COW in March 2015. Linear regressions with negative slopes were determined between the humic-like components and the salinity of COW. The intercepts of the regressions against the humic-like components were within the ranges of those observed for the local rivers of Hokkaido but were very different from those of sea ice. These findings suggest that river water contributed to the COW observed here as a freshwater end-member, although the contribution of sea-ice melt water to COW could not be evaluated. This novel approach also highlighted two different less-saline water masses in COW. The first was characterized by a lower temperature and relatively high levels of humic-like components, while the second was higher in temperature and had higher levels of humic-like components. It is suggested that these different characteristics are due to the contributions of water from different rivers and/or different effects of sea-ice melt water.  相似文献