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11.
To investigate the distributions of dinoflagellate cysts in relation to environmental conditions from southern coast of Korea,
surface sediment samples collected from 11 stations in Gamak Bay, Yeoja Bay and the offshore area of Yeoja Bay were analyzed.
Dinoflagellate cyst assemblages observed in the study area included many species commonly reported from other temperate regions.
Among them, Polykrikos cysts were dominant, together with Brigantedinium spp. and Spiniferites spp. Based on cluster analysis, dinoflagellate cyst assemblages were divided into two main groups; group I, located in Yeoja
Bay and group II, located in Gamak Bay and the offshore area of Yeoja Bay. Principal component analysis identified differences
in salinity levels as the main environmental factors affecting the distributional characteristics of dinoflagellate cyst assemblages
in the study area. Gamak Bay is a typical eutrophied area as result of extensive human activities around the bay, and heterotrophic
cysts, including Polykrikos cysts, are remarkably abundant and likely to be a useful indicator for eutrophication in Gamak Bay. 相似文献
12.
Microbial community respiration and structure of dead zone sediments of Omura Bay, Japan 总被引：1，自引：0，他引：1
Minoru Wada Shotaro Suzuki Tadashi Nara Yu Umezawa Motohiro Shimanaga Kazumi Matsuoka Hideaki Nakata 《Journal of Oceanography》2012,68(6):857-867
Monitoring sediment microbial community metabolism and structure is instrumental to understanding biogeochemical processes in and ecological impacts on bottom environments. The aim of this study was to determine potential community respiration and to reveal community dynamics of the microorganisms in the dead zone sediments of Omura Bay, Japan. The bay is highly enclosed and develops severe hypoxia in the central regions every summer. We collected sediment core samples from the center of the bay during hypoxia, estimated sediment oxygen consumption by using an adapted in vivo electron transport system activity (in vivo ETSA) assay, enumerated abundance of bacteria, and analyzed bacterial community structure by automated ribosomal intergenic spacer analysis. Higher ETSA and bacterial diversity were found in upper sediments (within 3?cm depth) from the center than the fringe of the bay. Sediment bacterial community structure of the bay center was distinct from that of the fringe. From these results, upper sediment in the dead zone of Omura Bay was characterized by (1) greater community respiration and (2) greater diversity of bacterial components compared with the non-hypoxic sediment of the bay fringe. These characteristics have important implications for understanding the interaction between microbial communities and the development of hypoxia in Omura Bay. 相似文献
13.
TATSUYA WATANABE NORIKAZU MATSUOKA HANNE H. CHRISTIANSEN 《Geografiska Annaler: Series A, Physical Geography》2012,94(4):445-457
Arctic tundra surfaces are dominated by a variety of patterned ground forms. Whereas a large number of studies have described morphology, structure and processes of patterned ground, few have monitored detailed patterned ground dynamics and subsurface environments continuously. We applied electrical resistivity tomography (ERT) to understand near‐surface conditions of two types of patterned ground, ice‐wedge polygons and mudboils in Svalbard, where periglacial processes associated with permafrost are intensively monitored. Automated monitoring shows surface movement characterized by annual cycles of frost heave and thaw settlement, the amounts and rates of which are influenced by the intensity of ice segregation. A time series of ERT shows (1) a distinct resistivity boundary delimiting the active‐layer depth, (2) seasonal variation in resistivity controlled by thermo‐hydrological dynamics and (3) spatial variation in resistivity reflecting desiccation in summer and intensive ice segregation in winter. These results demonstrate ERT as a useful complementary technique for monitoring active‐layer depths and near‐surface hydrological conditions at periglacial patterned ground sites, where automated soil thermal and moisture measurements are limited. 相似文献
14.
15.
河口地层独居石Th(U)-Pb年龄对长江贯通时限的约束 总被引：6，自引：0，他引：6
新生代长江水系调整、东西贯通时限是国内外学者共同关注的问题。长江发展演化的复杂性在近一个世纪的河流沉积地貌学研究中得到充分的认识,但在贯通时限问题上难以形成共识。河口地层中碎屑独居石的电子探针Th(U)-Pb年龄较好地限定长江东西贯通的时间在2.58MaBP前后。随着碎屑矿物微区分析技术的发展,锆石、独居石年代学和微区特征将成为研究流域演化、构造运动的主要手段。 相似文献
16.
Hydrographic observations in Hidaka Bay, south of Hokkaido, Japan were carried out in late winter 1996 and 1997 to examine
the spatial distributions and circulation features of two different water masses, i.e., Coastal Oyashio Water (COW) and Tsugaru
Warm Water (TWW), and their modifications. It is known that COW is mostly composed of cold and low-salinity water of the melted
drift ice coming from the Okhotsk Sea and flows into Hidaka Bay from winter to spring and TWW with high-salinity continuously
supplies from the Tsugaru Strait to the North Pacific. Cold surface mixed layers (<26.2σθ, 0–100 m depth) were found mainly over the shelf slope, confirming that anti-clockwise flow of COW was formed. TWW was relatively
high in salinity and low in potential vorticity, and had some patch-like water masses with a temperature and salinity maximum
in the limited area in the further offshore at the deeper density levels of 26.6–26.8σθ. The fine structure of vertical temperature and salinity profiles appeared between TWW and COW is an indication of enhanced
vertical mixing (double-diffusive mixing), as inferred from the estimated Turner angles. At a mouth of the Tsugaru Strait
in late winter 1997, a significant thermohaline front between TWW and the modified COW was formed and a main path of TWW spreaded
south along the Sanriku coast, probably as the bottom controlled flow. Hence, the patch-like TWW observed in late winter is
isolated from the Tsugaru Warm Current and then rapidly modified due to a diapycnal mixing.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
17.
于 2 0 0 0— 2 0 0 1年采集了中国沿海 1 0个采样点的表层沉积物样品 ,研究了有毒亚历山大藻 (Alexandriumspp .)和链状裸甲藻 (Gymnodiniumcatenatum)孢囊的分布。结果表明 ,这两类孢囊几乎在所有采样点都检测到。链状裸甲藻孢囊虽分布广泛 ,但含量较低 ,在样品中的浓度和百分比含量分别为 0— 71 .1cysts/gDW和 0 %— 1 4.3%。亚历山大藻孢囊在大部分海域含量较低 ,而在PSP毒素中毒事件高发区和贝类PSP毒素高含量区的大亚湾大鹏澳海域却高密度、高频率地出现 ,最高密度为 366cysts/gDW。研究结果显示 ,大亚湾大鹏澳海域表层沉积物中高密度的亚历山大藻孢囊也许是该海域贝类体内冬季PSP毒素积累及高含量的重要原因之一。 相似文献
18.
Conglomerates of the Kuma Group, central Shikoku, southwest Japan contain Sanbagawa schist clasts with a variety of metamorphic grades and lithologies. K–Ar and 40 Ar/39 Ar dating of phengite show all the pelitic schist clasts from low- to high-grade zones have similar phengite ages (82–84 Ma) that are significantly older than those from the in situ Sanbagawa sequence of central Shikoku. This is because the Kuma–Sanbagawa sequence was exhumed earlier than the in situ Asemi sequence with an exhumation process intermediate between those for the Kanto Mountains and the in situ Asemi sequences. 40 A/39 Ar plateau ages (103 and 117 Ma) of phengite in amphibolites indicate the timing of the early stage of the exhumation of the metamorphic pile, probably close to the peak metamorphic age. 相似文献
19.
LI Wei WAN Xiaoqiao Atsushi MATSUOKA ZHANG Shuqin QU Haiying Tsubasa TAMURA Kohei YOSHINO 《《地质学报》英文版》2015,89(1):285-299
Defining the Jurassic-Cretaceous boundary is a controversy in stratigraphic study of the world. It has been widely accepted that this boundary can be defined at the bottom of Berriasian in Tethys, with the appearance of the ammonite Berriasella jacobi dating to ca. 145 Ma. However, it is difficult for the widespread terrestrial deposits in China to correlate with the international standard of marine facies. The Somanakamura Group in Japan is represented by a succession of marine-continental transitional strata. It provides a bridge of marine and nonmarine stratigraphic correlation. The ammonite and radiolarian fossils preserved in this group suggest an age from Bajocian to early Valanginian. The J-K boundary was defined in or atop the Tomizawa Formation of the group according to the ammonite data. The present authors study the fossil spores and pollen newly found from the Tomizawa and Koyamada formations. Three assemblages have been recognized. They are Assemblage 1 (Cyathidites-Classopollis) from the upper part of the Tomizawa Formation, Assemblage 2 (Cyathidites-Jiaohepollis) from the lower part of the Koyamada Formation, and Assemblage 3 (Cyathidites-Spheripollenites-Ephedripites) from the middle to upper part of the Koyamada Formation. With the reference of ammonite evidence, the J-K boundary can be defined between Assemblage 1 and Assemblage 2. This palynological J-K boundary can be correlated with that of terrestrial sequence in China. However, local biostratigraphy imply that the continental J-K boundary in China is of 135 or 137 Ma age. It has a considerable discrepancy from the marine standard. Biogeographically, the distribution pattern of spores and pollen in southern China is in accordance with that in the Somanakamura Group, which parallels the Tuchengzi Formation in northeastern China. By the palynological correlation between the Somanakamura Group and the strata in southern China, and then with the sequence in northeastern China, it is suggested that the continental J-K boundary is located in the Tuchengzi Formation. 相似文献
20.
Various types of endocrine disruptors or environmental hormones flow from their sources down into harbours through rivers and other watercourses, and are accumulated in sediment on the sea bottom. Tributyltin, which has been used as paint for ship bottoms, is considered one of the endocrine disruptors.In close cooperation with the other ministries and agencies, the Ports and Harbours Bureau of the Ministry of Land, Infrastructure and Transport carried out an investigation in 1999 to determine the actual condition of 12 endocrine disruptors in the sediment of 39 harbours, in order to gather fundamental data to be used in future examinations of policy. Furthermore, in 2000 the bureau chose seven harbours out of the above 39 harbours as subjects of an additional investigation regarding the surface distribution of endocrine disruptors in the harbour areas and the synchronistic change of accumulation of dioxin and other substances. As the result of the investigation regarding the surface distribution of endocrine disruptors accumulated in seven harbours, relatively high concentrations were measured in the innermost parts of harbours and the mouths of rivers. Synchronistic changes in the amount of dioxin and other substances accumulated in sediments of five harbours were determined. Small amounts of dioxin and other substances, including an especially small amount of coplanar-PCBs, were found in the layers formed before or around 1950. Relatively large amounts of these substances were measured in the upper layers formed during roughly 1960-1990, though no significant yearly differences in concentration could be identified. This result coincides with the facts that, during roughly 1960-1980, PCP and CNP were used as agricultural chemicals and full-scale production of PCBs started in 1960. 相似文献