Phytoplankton community reorganization driven by eutrophication and warming in Lake Biwa   总被引：1，自引：0，他引：1  

Chih Hao Hsieh  Kanako Ishikawa  Yoichiro Sakai  Toshiyuki Ishikawa  Satoshi Ichise  Yoshimasa Yamamoto  Ting Chun Kuo  Ho Dong Park  Norio Yamamura  Michio Kumagai 《Aquatic Sciences - Research Across Boundaries》2010,72(4):467-483

We compiled and analyzed long-term data, including chemical, physical and phytoplankton community data, for the Lake Biwa ecosystem from 1962 to 2003. Analyses on environmental data indicate that Lake Biwa had experienced intensified eutrophication (according to total phosphorus concentration) in the late 1960s and returned to a less eutrophic status around 1985, and then exhibited rapid warming and thus increased water column stability since 1990. Total phytoplankton cell volume largely followed the trend of total phosphorus concentration, albeit short-term fluctuations existed. However, phytoplankton community shifted dramatically in response to those changes of environmental states. These shifts were cause by changes in trophic status driven by phosphorus loadings and physical properties in the water column driven by warming. Moreover, most phytoplankton species did not show a strong linear correlation with environmental variables, suggesting nonlinear transitions among different states.  相似文献   

青藏高原复杂地表能量通量研究   总被引：4，自引：0，他引：4  

马耀明  姚檀栋  王介民  胡泽勇  石川裕彦  马伟强  M. Menenti  苏中波 《地球科学进展》2006,21(12):1215-1223

“全球能量水循环之亚洲季风青藏高原试验研究”（GAME/Tibet）和“全球协调加强观测计划（CEOP）亚澳季风之青藏高原试验研究”（CAMP/Tibet）的加强期观测和长期观测已经进行了9年多,并且已取得了大量的珍贵资料。首先介绍了GAME/Tibet 和CAMP/Tibet 试验的情况,并利用观测资料给出了局地能量分布（日变化和月际变化）特征。复杂地表区域能量通量研究是青藏高原地气相互作用研究中的重中之重。卫星遥感的应用成为解决这一问题,即实现GAME/Tibet和CAMP/Tibet试验主要初衷的必不可少的手段。利用卫星遥感观测（Landsat 7 ETM）资料结合地面观测的方法,计算得到了相关地区非均匀地表区域上的地表温度、地表反射率、标准化差值植被指数(NDVI)、校准的调整土壤植被指数（MSAVI）、植被覆盖度和叶面指数(LAI)及能量平衡各分量（净辐射通量、土壤热通量、感热和潜热通量）的分布图像,所得结果基本可信。为了得到整个青藏高原复杂地表的热通量分布,中国科学院青藏高原研究所正在与其他研究单位一起建立青藏高原地表和大气过程监测系统（MORP）。最后介绍了该监测计划和已建立的3个综合观测研究站及如何利用建立的台站把站点观测的热通量推广到整个青藏高原的途径。  相似文献   

中国大陆地壳应力场与构造运动区域特征研究   总被引：41，自引：16，他引：25       下载免费PDF全文

徐纪人  赵志新  石川有三 《地球物理学报》2008,51(3):770-781

系统研究了1918～2006年间中国大陆及其周缘发生的3115个M4.6以上中、强地震的震源机制解,得到中国大陆地壳区域应力场的压应力轴和张应力轴空间分布的统计结果.探讨了大陆应力场的结构,以及周围板块运动对中国大陆应力场影响作用范围及其界线.结果表明,中国东部的华北地区受到太平洋板块向欧亚板块俯冲挤压的同时,又受到从贝加尔湖经过大华北直至琉球海沟的广阔范围内存在的方位为170°引张应力场的控制.华北地区大地震的震源机制解反映出,该区地震发生为NEE向挤压应力和NNW向张应力的共同作用结果.印度洋板块向欧亚板块的碰撞挤压运动所产生的强烈的挤压应力,控制了喜马拉雅、青藏高原、乃至延伸到天山及其以北的广大地区.在青藏高原周缘地区和中国西部的大范围内,压应力P轴水平分量位于20°~40°,形成了近北东方向的挤压应力场,大量逆断层型强震集中发生在青藏高原的南、北和西部周缘地区以及天山等地区. 本文结果表明,正断层型地震集中发生在青藏高原中部高海拔的地区.证明了青藏高原周缘区域发生南北向强烈挤压短缩的同时,中部高海拔地区存在着明显的近东西向的扩张运动.根据本文最新结果,得到了华北、华南块体之间地壳区域应力场的控制边界线,发现该分界线与大地构造、岩石圈板块构造图等有较大差异,特别是在大别及其以东地区, 该分界线向东南偏转,在沿海的温州附近转向东,最终穿过东海直至琉球海沟.台湾纵谷断层是菲律宾海板块与欧亚板块之间碰撞挤压边界,来自北西西向运动的菲律宾海板块构造应力控制了从台湾纵谷、华南块体,直到中国南北地震带南段东部地域的应力场. 地震震源机制结果还表明,南北地震带南段西侧其P轴大约为NNE方向,与青藏高原的P轴方位一致.南北地震带南段东侧其P轴大约为NWW方向,与华南块体的P轴方位一致.因此,将中〖JP2〗国大陆分成东、西两部分的南北地震带南段是印度洋板块与菲律宾海板块在中国大陆内部影响控制范围的分界线.  相似文献   

Occurrence of PSP-producing dinoflagellate Alexandrium tamiyavanichii in Bingo-Nada, the central coastal water of the Seto Inland Sea, Hiroshima Prefecture, Japan     

Beppu R  Nojima K  Tsuruda S  Gomez-Delan G  Barte-Quilantang M  Taniyama S  Sagara T  Nishio S  Takayama H  Miyazawa K  Asakawa M 《Marine pollution bulletin》2008,56(4):758-763

During surveillance of the distribution of the paralytic shellfish poison (PSP)-producing dinoflagellate in 2003, 2004 and 2005 along the coastlines of the Seto Inland Sea, Hiroshima Prefecture, Japan, some species of toxic phytoplankton were isolated from the eastern coasts, Bingo-Nada, the central regions of the Seto Inland Sea. It was rather unexpectedly revealed from the basis of the morphological characteristics that they were unambiguously identified as Alexandrium tamiyavanichii and Alexandrium catenella. Two strains (ATY041106, ATY051018) of A. tamiyavanichii showed a specific toxicity of 38.7 x 10(-6) and 111.5 x 10(-6)MU/cell, respectively. These values seemed to be several times or much higher than that of A. catenella (AC030816, AC040614), having a specific toxicity of 4.5 x 10(-6) and 4.1 x 10(-6)MU/cell, respectively, isolated in the same area. From the results of HPLC-furuorometric analysis, it revealed that the toxins in ATY041106 exist almost exclusively as beta-epimers (C2, GTX3, GTX4), which accounted for 72.7 mol%. The toxin profiles of this strain are featured by the presence of a large amount of GTX3 (59.1 mol%) and a small amount (20.6%) of C1 and 2 in comparison with the PSP compositions of A. tamarense, which is isolated as the main responsible species in Hiroshima Bay, a western part of coastal sea in Hiroshima Prefecture. On the other hand, it revealed that the toxin profiles of two strains (AC030816, AC040614) of A. catenella exist almost exclusively as beta-epimers (C2, GTX3, GTX4), which accounted for 81.8 and 56.5 mol%, as the same manner. The toxin profiles of these two strains are featured by the presence of a large amount of C2 (80.5 and 46.3 mol%) in comparison with the PSP compositions of A. tamiyavanichii. To our knowledge, this is the first record to show the distribution and harmful influence of A. tamiyavanichii and A. catenella in Bingo-Nada in Hiroshima Prefecture. Though contamination of bivalves with these PSP-producing planktons in this area has not occurred yet so far, attention should be paid to this species as well as the other causative dinoflagellate from the stand point of public health and food hygiene.  相似文献   

Chemostratigraphy of the Ediacaran basinal setting on the Yangtze platform,South China: Oceanographic and diagenetic aspects of the carbon isotopic depth gradient          下载免费PDF全文

Seishiro Furuyama  Akihiro Kano  Yoko Kunimitsu  Tsuyoshi Ishikawa  Wei Wang  Xin‐chun Liu 《Island Arc》2017,26(5)

The Ediacaran Yangtze platform in South China, which represents depositional settings ranging from coastal to basinal, provides valuable information for understanding climate changes and animal evolution during the Ediacaran Period. Although the shallower settings have been investigated, research on the basinal sections has been limited. This has hampered efforts to establish stratigraphic correlations and understand the oceanographic setting of the Yangtze platform. In this paper, the chemostratigraphy of a basinal section at Fengtan, Hunan Province, is reported based on analyses of stable carbon isotope profiles in carbonates (δ¹³C_carb), organic matter (δ¹³C_org), total organic carbon, ⁸⁷Sr/⁸⁶Sr ratios, and Mn, Rb, and Sr concentrations. The basinal section of the Doushantuo Formation, which is represented at Fengtan, provides data supporting regional correlations and oceanography. Three intervals in the Doushantuo Formation are correlated with the Three Gorges: (i) a negative δ¹³C_carb anomaly with stable δ¹³C_org values and altered ⁸⁷Sr/⁸⁶Sr ratios in the lower section can be correlated to the boundary between Doushantuo Members 2 and 3 (Interval A); (ii) a relatively high δ¹³C_carb anomaly with unaltered ⁸⁷Sr/⁸⁶Sr ratios (up to 0.7086) in the middle section corresponding to the lower part of Doushantuo Member 3 (Interval B); and (iii) a negative δ¹³C_carb anomaly with lowered δ values in the upper section can be correlated to the long interval of negative δ¹³C_carb (Interval C). The Gaskiers glaciation is likely represented in Interval A, and Interval C corresponds to the Shuram excursion reported for other Ediacaran localities. Our correlations confirm the depth gradient of δ¹³C_carb in the Yangtze platform and imply that reductive conditions prevailed in the basinal section from the Early to Middle Ediacaran. Under such conditions, anaerobic degradation of organic carbon or methane perturbed the inorganic carbon isotopic compositions and was at least partly responsible for the depth gradient of δ¹³C_carb.  相似文献   

Importance of eddy representation for modeling the intermediate salinity minimum in the North Pacific: Comparison between eddy-resolving and eddy-permitting models     

Ichiro Ishikawa  Hiroshi Ishizaki 《Journal of Oceanography》2009,65(3):407-426

In order to confirm the results of the authors’ previous work, which found that the existence of disturbances smaller than meso-scale eddies is important in large-scale mixing process between the Oyashio and Kuroshio waters in the intermediate layer, the results of an eddy-resolving model experiment are analyzed and compared with those of an eddy-permitting model. The intermediate salinity minimum given in the initial condition weakens as integration advances in the eddy-permitting model, while it recovers rapidly and is maintained thereafter in the eddy-resolving model, initialized from the unrealistic salinity distribution of the former. Filament-like fine structures in temperature and salinity develop actively in the latter, which are much smaller in horizontal width than meso-scale eddies, suggesting the importance of such disturbances in the large-scale mixing. The mixing ratio of the Oyashio water defined by the original Oyashio and Kuroshio waters shows that its value is generally higher in the intermediate lower sub-layer than in the intermediate upper sub-layer in the Mixed Water Region, and the salinity minimum exists between layers with low and high values of the mixing ratio with its strong vertical gradient. The eddy transports of the Oyashio and Kuroshio waters in an isopycnal layer are divided into four components, usual isopycnal mixing of temperature and salinity being dominant, followed by the component associated with the thickness flux. The southward eddy transport of the Oyashio water and the northward eddy transport of the Kuroshio water are not symmetric to each other because the thickness-flux-associated components are in the same direction (southward).  相似文献   

Influence of the Atmospheric Model on Hanle Diagnostics     

Ryohko Ishikawa  Han Uitenbroek  Motoshi Goto  Yusuke Iida  Saku Tsuneta 《Solar physics》2018,293(5):74

We clarify the uncertainty in the inferred magnetic field vector via the Hanle diagnostics of the hydrogen Lyman-\(\upalpha\) line when the stratification of the underlying atmosphere is unknown. We calculate the anisotropy of the radiation field with plane-parallel semi-empirical models under the nonlocal thermal equilibrium condition and derive linear polarization signals for all possible parameters of magnetic field vectors based on an analytical solution of the atomic polarization and Hanle effect. We find that the semi-empirical models of the inter-network region (FAL-A) and network region (FAL-F) show similar degrees of anisotropy in the radiation field, and this similarity results in an acceptable inversion error (e.g., \({\sim}\, 40~\mbox{G}\) instead of 50 G in field strength and \({\sim}\,100^{\circ}\) instead of \(90^{\circ}\) in inclination) when FAL-A and FAL-F are swapped. However, the semi-empirical models of FAL-C (averaged quiet-Sun model including both inter-network and network regions) and FAL-P (plage regions) yield an atomic polarization that deviates from all other models, which makes it difficult to precisely determine the magnetic field vector if the correct atmospheric model is not known (e.g., the inversion error is much larger than 40% of the field strength; \({>}\,70~\mbox{G}\) instead of \(50~\mbox{G}\)). These results clearly demonstrate that the choice of model atmosphere is important for Hanle diagnostics. As is well known, one way to constrain the average atmospheric stratification is to measure the center-to-limb variation of the linear polarization signals. The dependence of the center-to-limb variations on the atmospheric model is also presented in this paper.  相似文献   

Improved description of global mixed-layer depth using Argo profiling floats     

Shigeki Hosoda  Tsuyoshi Ohira  Kanako Sato  Toshio Suga 《Journal of Oceanography》2010,66(6):773-787

A global data set describing the gridded mixed-layer depth (MLD) in 10-day intervals was produced using high-quality Argo float data from 2001 to 2009. The characteristics and advantages provided by the new MLD data set are described here, including a comparison based on two different thresholds and using data sets of different vertical and temporal resolution. The MLD in the data set was estimated on the basis of a shallower depth of the iso-thermal layer (TLD) or iso-pycnal layer (PLD), calculated using the finite difference method. The MLD data are incorporated into 2° × 2° grid in the global ocean, including marginal seas. Also, two threshold values were used to examine differences in the MLD and its seasonal temporal variability. The characteristics and advantages of using the Argo 10-day intervals to determine the MLD were then confirmed by comparing those data with the station buoy daily means and the Argo monthly means. With respect to vertical and temporal resolutions, the Argo 10-day data has two distinct advantages: (1) improved representation of the MLD vertical change due to high vertical resolution, especially during periods of large MLD variability and (2) more detailed representation of the temporal change in MLD than achieved with the Argo monthly mean data, especially from winter to spring in mid and high latitudes. These advantages were maintained in the case of a larger threshold despite the fact that the MLD is rather deep and the detailed variation in its distribution differs depending on the season and location. This study also investigated the relative influence of TLD and PLD to the MLD calculation for each grid. Generally, the MLD is primarily determined based on the PLD at low and mid latitudes (TLD > PLD), whereas the TLD is more important at high latitudes, especially in winter (TLD < PLD). In the case of a larger threshold, the area of the larger PLD influence spreads polewards because of the greater effect of salinity in winter. Although there are some differences in the effect of temperature and salinity in estimations of the MLD, both are indispensable factors for the MLD estimations even at different thresholds.  相似文献   

Additional flux arising from unresolved scales in eddying ocean models     

Mikitoshi Hirabara  Hiroshi Ishizaki  Goro Yamanaka  Hiroyuki Tsujino  Ichiro Ishikawa 《Journal of Oceanography》2010,66(5):633-647

An analysis is presented of snapshot data (eastward and northward velocity components: u and v; tracer such as potential temperature: τ) from an eddy-resolving (Rgrid: 1/12°) ocean model experiment, in order to explore a method for improving eddy-permitting model performance. Horizontal 3 × 3 R-grid averages give the eddy-permitting grid (P-grid: 1/4°) variables: 〈u〉, 〈v〉, and 〈τ〉, where 〈〉 denotes the spatial P-grid scale average. The difference between the horizontal tracer flux across the boundary face of a P-grid and that across the corresponding faces of R-grids is estimated as F_2E. It is found that the correlations among the gradients of u, v, and τ give a good approximation F_2C to the estimated flux F_2E. The approximated flux is a function of these gradients and the grid size. A method is presented for implementing the F_2C for density to an eddying ocean model as an additional advection. Practical experiments were conducted with a realistic configuration. It is shown that the zonal mean isotherms in the Kuroshio extension region are more flattened in the run using the proposed method than in another run using the conventional horizontal biharmonic operator, suggesting that the additional flux correction leads to an enhancement of sub-basin scale mixing.  相似文献   

Collisional bending of the western Paleo‐Kuril Arc deduced from paleomagnetic analysis and U–Pb age determination     

Takahiro Katagiri  Hajime Naruse  Naoto Ishikawa  Takafumi Hirata 《Island Arc》2020,29(1)

The Paleo‐Kuril Arc in the eastern Hokkaido region of Japan, the westernmost part of the Kuril Arc in the northwestern Pacific region, shows a tectonic bent structure. This has been interpreted, using paleomagnetic data, to be the result of block rotations in the Paleo‐Kuril Arc. To understand the timing and origin of this tectonic bent structure in the Paleo‐Kuril arc‐trench system, paleomagnetic surveys and U–Pb radiometric dating were conducted in the Paleogene Urahoro Group, which is distributed in the Shiranuka‐hill region, eastern Hokkaido. The U–Pb radiometric dating indicated that the Urahoro Group was deposited at approximately 39 Ma. Paleomagnetic analysis of the Urahoro Group suggested that the Shiranuka‐hill region experienced a 28° clockwise rotation with respect to East Asia. The degree of clockwise rotation implied from the Urahoro Group is smaller than that of the underlying Lower Eocene Nemuro Group (62°) but larger than that of the overlying Onbetsu Group (?9°). It is thus suggested that the Shiranuka‐hill region experienced a clockwise rotation of approximately 34° between the deposition of the Nemuro and Urahoro Groups (50–39 Ma), and a 38° clockwise rotation between the deposition of the Urahoro and Onbetsu Groups (39–34 Ma). The origin of the curved tectonic belt of the Paleo‐Kuril Arc was previously explained by the opening of the Kuril Basin after 34 Ma. The age constraint for the rotational motion of the Shiranuka‐hill region in this study contradicts this hypothesis. Consequently, it is suggested that the process of arc–arc collision induced the bent structure of the western Paleo‐Kuril Arc.  相似文献