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81.
82.
Tsurane Kuragano Yosuke Fujii Takahiro Toyoda Norihisa Usui Koji Ogawa Masafumi Kamachi 《Journal of Oceanography》2014,70(1):45-62
A consistency between seasonal fluctuation of actual sea surface height (SSH) and those caused by mass and density variations in gyre-scale regions is examined. The SSH obtained from satellite altimetry (altimetric SSH) is adopted as the actual SSH. SSH caused by mass variation (mass-related SSH) is simulated using a barotropic global ocean model forced by water flux, wind stress and surface pressure. SSH caused by density variation (steric SSH) is calculated from water density profile, i.e. temperature and salinity profiles. The model SSH well represents mass-related SSH for gyre-scale regional means, and seasonal fluctuation of the altimetric SSH corrected for the model SSH is similar to that of steric SSH above a pressure level larger than 300 dbar. The results indicate that the mass-related SSH does not much respond to the baroclinic adjustment to the seasonally varying wind stress curl. The mass-related SSH forced by wind stress and surface pressure should be accounted for regional evaluation, though it is not necessary for global mean evaluation. Detection of steric SSH from altimetric SSH would be useful for assimilation approaches in which the altimetric SSH is treated as the variable reflecting subsurface temperature and salinity. 相似文献
83.
Hiroyuki Takata Satoshi Tanaka Koji Seto Saburo Sakai Katsumi Takayasu Boo-Keun Khim 《Journal of Paleolimnology》2014,51(3):421-435
We investigated responses of shallow-water benthic foraminifera to changes in climate and ocean conditions, using sediment core ASC2 from Aso-kai lagoon, central Japan. Six AMS 14C dates reveal that the studied interval corresponds to sediments deposited from ~AD 700 to 1600. Sulfur content of the bulk sediment and multi-dimensional scaling (MDS) axis 1 of fossil benthic foraminifera indicate that the composition of the benthic foraminifera community was closely related to dissolved oxygen (DO) concentration in the hypolimnion. The sulfur content and MDS axis 1 also revealed two shifts over the 900-year interval. In the first phase (~AD 700–1250), the Shannon–Wiener Index (H′), E (S200), evenness and rank abundance curve (RAC) kurtosis indicate a gradual deterioration in structure of the benthic foraminifera community. In that period, there are statistically significant correlations between the faunal composition (MDS axis 1) and faunal structure [Shannon–Wiener (H′), E (S200), evenness and RAC kurtosis]. In the second phase (~AD 1250–1600), however, faunal composition and structure show no marked correspondence. Instead, abundance of benthic foraminifera fluctuated on a scale of ~200 years. Thus, a shift in the biotic response of benthic foraminifera in Aso-kai lagoon occurred in ca. AD 1250. Gradual deterioration of benthic foraminifera, with taxonomic losses, is consistent with declining DO in the first phase, possibly associated with the increasing influence of the Tsushima Warm Current. The possibility that closure of Aso-kai lagoon and development of the sand bar affected benthic foraminifera cannot, however, be ruled out. No corresponding response was observed in the second phase, during which there was no distinct taxonomic loss. Large variations in abundance, however, were a consequence of strength of the East Asian summer and winter monsoons. The shift in the biotic response of benthic foraminifera in Aso-kai lagoon during the period AD 700–1600 was apparently a result of changes in climate and ocean conditions on the East Asian continental margin. 相似文献
84.
85.
86.
NOAA/AVHRR Global Vegetation Index (GVI) data of Asia in 1983 and 1987 were used to evaluate their usefulness for global land cover monitoring. Color composite images of monthly GVI data and color composite images of principal components from 12 successive monthly GVI data were found to be useful for visual interpretation of seasonal vegetation dynamics. The results of cluster analysis applied to monthly GVI data for a one‐year period, indicate that unsupervised classification method is useful for global or continental land cover classification without ground truth. In order to detect land cover changes, the difference between the 1983 and 1987 12‐month GVI data was calculated. The results show that it is difficult to detect land cover changes due to cloud contamination in monthly GVI data and poor registration of GVI products. 相似文献
87.
The point at issue: The Kurosegawa Terrane is composed of continental fragments transecting Mesozoic terranes of accretionary complex in Southwest Japan (Fig. 1). It is an attenuated tectonic sliver and considered to be allochthonous with respect to the main part of Southwest Japan. The problem of which continental block in the East Asian continental margin is the source of the Kurosegawa Terrane has puzzled Japanese geologists for many years.
Firstly, we try to approach this issue based on the analysis of fusulinacean assemblage in accreted terranes composed of subduction complex in the Pacific Rim.
Secondly, by applying the result of this analysis we try to locate the source of the continental fragments of the Kurosegawa Terrane.
Thirdly, we try to prove its validity with a new paleomagnetic study. 相似文献
88.
Yuya Tada Akito Taniguchi Yuki Sato-Takabe Koji Hamasaki 《Journal of Oceanography》2012,68(4):509-519
Our objective was to track microbial processes associated with serial degradation of organic matter derived from algal blooms. To do this, we analyzed population fluctuations and growth responses of major phylogenetic groups of free-living marine bacteria. We used bromodeoxyuridine immunocytochemistry–fluorescence in situ hybridization methodology to examine marine bacterial community development during and after a diatom bloom in a mesocosm. We revealed that the Roseobacter/Rhodobacter, SAR11, Alteromonas, and Bacteroidetes groups were clearly major phylotypes responsible for most free-living bacterial biomass and production throughout the experiment. The clearest bacterial response was a proliferation of the Alteromonas group (cells with large volumes) during development of the bloom (up to 30?% of actively growing cells). Populations of these bacteria declined sharply thereafter, likely due to grazing. Alteromonas group responses suggest that these bacteria strongly influenced the flux of organic matter at an early bloom stage. The growth potential of Bacteroidetes was relatively large as the bloom peaked; this early development probably contributed to the initial stage of bloom decomposition. In contrast, the contribution of Roseobacter/Rhodobacter to total bacterial production increased at a late stage of decomposing of the bloom. The contributions of Betaproteobacteria, SAR11, and SAR86 groups to total bacterial abundance and production were relatively minor throughout the experiment. These results imply that the ability to utilize organic matter derived from diatoms varies among bacterial phylotypes, and, frequently, less abundant but ecological specialist taxa such as Alteromonas may play major roles in the flux of organic matter during diatom blooms. 相似文献
89.
Takeshi Yoshimura Koji Suzuki Hiroshi Kiyosawa Tsuneo Ono Hiroshi Hattori Kenshi Kuma Jun Nishioka 《Journal of Oceanography》2013,69(5):601-618
Response of phytoplankton to increasing CO2 in seawater in terms of physiology and ecology is key to predicting changes in marine ecosystems. However, responses of natural plankton communities especially in the open ocean to higher CO2 levels have not been fully examined. We conducted CO2 manipulation experiments in the Bering Sea and the central subarctic Pacific, known as high nutrient and low chlorophyll regions, in summer 2007 to investigate the response of organic matter production in iron-deficient plankton communities to CO2 increases. During the 14-day incubations of surface waters with natural plankton assemblages in microcosms under multiple pCO2 levels, the dynamics of particulate organic carbon (POC) and nitrogen (PN), and dissolved organic carbon (DOC) and phosphorus (DOP) were examined with the plankton community compositions. In the Bering site, net production of POC, PN, and DOP relative to net chlorophyll-a production decreased with increasing pCO2. While net produced POC:PN did not show any CO2-related variations, net produced DOC:DOP increased with increasing pCO2. On the other hand, no apparent trends for these parameters were observed in the Pacific site. The contrasting results observed were probably due to the different plankton community compositions between the two sites, with plankton biomass dominated by large-sized diatoms in the Bering Sea versus ultra-eukaryotes in the Pacific Ocean. We conclude that the quantity and quality of the production of particulate and dissolved organic matter may be altered under future elevated CO2 environments in some iron-deficient ecosystems, while the impacts may be negligible in some systems. 相似文献
90.
Flow resistance of one-line emergent vegetation along the floodplain edge of a compound open channel
Experiments have been conducted in straight compound channels with and without one-line emergent vegetation along the floodplain edge, in which stream-wise velocities and boundary shear stresses have been measured. The experimental results show that the velocity distribution in the vegetation case is considerably different from that in the no vegetation case and the boundary shear stress is also significantly reduced by the additional flow resistance caused by the vegetation at a similar relative water depth. The apparent shear stress distribution which has been calculated with the boundary shear stress and weight component in the vegetation case is totally different from that in the no-vegetation case. New formulae for friction factors for the with and without vegetation cases are developed using vegetation density and flow parameters. The drag force caused by the vegetation is obtained for two different vegetation density cases and the magnitude of its effect on total flow resistance is then investigated. The force balance method is used to predict discharge and this is compared with the discharge predicted by the new formula. A further analysis of the selection of vegetation spacing is carried out, determining its effect on stage-discharge. 相似文献