Iron deficiency in micro-sized diatoms in the Oyashio region of the Western subarctic Pacific during spring     

Ai Hattori-Saito  Jun Nishioka  Tsuneo Ono  R. Michael L. McKay  Koji Suzuki 《Journal of Oceanography》2010,66(1):105-115

In order to detect iron (Fe) stress in micro-sized (20–200 μm) diatoms in the Oyashio region, western subarctic Pacific during spring, immunological ferredoxin/flavodoxin assays were applied to samples collected from the surface layer in May 2005. Concomitantly, the community composition of the micro-sized phytoplankton and hydrographic conditions, including dissolved Fe and macronutrient concentrations, were also examined. Chlorophyll (Chl) a concentrations were <2 mg m⁻³ at all sampling stations, except at a station where the Chl a level was 9.0 mg m⁻³ and a micro-sized diatom bloom occurred. A high abundance of ferredoxin in micro-sized diatoms was detected only at a rather near-shore station where dissolved Fe and macronutrient concentrations were higher, indicating that the micro-sized diatoms did not suffer from iron deficiency. On the other hand, flavodoxin in micro-sized diatoms was often observed at the other stations, including the bloom station, where macronutrients were replete but dissolved Fe concentration was low (0.31 nM). A significant amount of chlorophyllide a, a degradation product of Chl a, was also observed at the bloom station, suggesting a decline of the diatom bloom. The micro-sized phytoplankton species at all the stations were mainly composed of the diatoms Thalassiosira, Chaetoceros, and Fragilariopsis spp. Our study indicates that micro-sized diatoms were stressed by Fe bioavailability during the spring season in the Oyashio region  相似文献   

Effect of human activity on Lake Saroma (Japan) during the past 150 years: Evidence by variation of diatom assemblages     

Kota Katsuki  Koji Seto  Ritsuo Nomura  Kimihiko Maekawa  Boo-Keun Khim 《Estuarine, Coastal and Shelf Science》2009

Diatom assemblages of the surface and in core sediment samples from Lake Saroma (Japan) were examined for the purpose of evaluating anthropogenic effect on the coastal environmental changes. Before the first inlet excavation, the lake's water quality and ecology were controlled by water exchange with the Okhotsk Sea as well as lake-level variation. However, large-scale ecological modification occurred, mainly due to artificial excavation and shellfish industrial farms. A distinct record of the succession of the dominant diatom taxa was preserved in core sediments. Low-oxygen water was prevalent in the lake in 1929, before the first inlet excavation. Immediately after the first inlet excavation, the low-oxygen water in the western basin of the lake began to disappear, in a trend that became increasing transparent, which has been attributed to an increasing rate of water exchange. However, the lacustrine environment of bottom sediments resumes deterioration 20 years after since the first artificial excavation: the resultant deposition of river-mouth materials into the deep basin caused eutrophication and environmental disturbance of the lake bottom. At the same time, the eutrophication of surface water became intensified with the onset of intense scallop culturing beginning in 1966. Increasing organic loads deposited onto the bottom layer in the form of excreta from the scallop nursery led to more oxygen deficiency and the elution of nitrogen and phosphorus from the sediment, which again brought about eutrophication of the surface layer. Such environmental change was reflected in a decrease of benthic diatom taxa and an increase of planktonic taxa, trends which have continued until today. Particularly, the numbers of diatom assemblage have been decreasing all over the lake during the last 10 years, which suggests that Lake Saroma's present-day deterioration and eutrophication will continue or become even worse.  相似文献   

Food sources of the pearl oyster in coastal ecosystems of Japan: Evidence from diet and stable isotope analysis   总被引：1，自引：0，他引：1  

Kayoko Fukumori  Misa Oi  Hideyuki Doi  Noboru Okuda  Hitomi Yamaguchi  Michinobu Kuwae  Hitoshi Miyasaka  Kenji Yoshino  Yoshitsugu Koizumi  Koji Omori  Hidetaka Takeoka 《Estuarine, Coastal and Shelf Science》2008

We estimated the composition of two food sources for the cultured pearl oyster Pinctada fucata martensii using stable isotopes and stomach content analysis in the coastal areas of the Uwa Sea, Japan. The δ¹³C values of oysters (−17.5 to −16.8‰) were intermediate between that of particulate organic matter (POM, −20.2 to −19.1‰) and attached microalgae on pearl cages (−13.0‰). An isotope mixing model suggested that oysters were consuming 78% POM (mainly phytoplankton) and 22% attached microalgae. The attached microalgal composition of the stomach content showed a strong resemblance to the composition of that estimated through the isotope mixing model, suggesting preferential utilization of specific components is unlikely in this species. These results indicate that P. fucata martensii feed on a mixture of phytoplankton and attached microalgae, and that the attached microalgae on pearl cages can serve as an important additional food source.  相似文献   

Modeling seasonal variations of ocean and sea ice circulation in the Beaufort and Chukchi Seas： A model-data fusion study     

Kohei Mizobata  Walter Johnson  Koji Shimada  Moto Ikeda 《极地研究(英文版)》2008,19(2):168-184

A 3.8-kin Coupled Ice-Ocean Model （C1OM） was implemented to successfully reproduce many observed phenomena in the Beaufort and Chukchi seas, including the Bering-inflow-originated coastal current that splits into three branches： Alaska Coastal Water （ACW） , Central Channel, and Herald Valley branches. Other modeled phenomena include the Beaufort Slope Current （BSC） , the Beaufort Gyre, the East Siberian Current （ ESC）, mesoscale eddies, seasonal landfast ice, sea ice ridging, shear, and deformation. Many of these downscaling processes can only be captured by using a high-resolution CIOM, nested in a global climate model. The seasonal cycles for sea ice concentration, thickness, velocity, and other variables are well reproduced with Solid validation by satellite measurements. The seasonal cycles for upper ocean dynamics and thermodynamics are also well reproduced, which include the formation of the cold saline layer due to the injection of salt during sea ice formation, the BSC, and the subsurface upwelling in winter that brings up warm, even more saline Atlantic Water along the shelfbreak and shelf along the Beaufort coast.  相似文献   

Impacts of global warming on hydrological cycles in the Asian monsoon region   总被引：1，自引：0，他引：1  

Koji DAIRAKU  Seita EMORI  Toru NOZAWA 《大气科学进展》2008,25(6):960-973

The hydrologic changes and the impact of these changes constitute a fundamental global-warmingrelated concern. Faced with threats to human life and natural ecosystems, such as droughts, floods, and soil erosion, water resource planners must increasingly make future risk assessments. Though hydrological predictions associated with the global climate change are already being performed, mainly through the use of GCMs, coarse spatial resolutions and uncertain physical processes limit the representation of terrestrial water/energy interactions and the variability in such systems as the Asian monsoon. Despite numerous studies, the regional responses of hydrologic changes resulting from climate change remains inconclusive. In this paper, an attempt at dynamical downsealing of future hydrologic projection under global climate change in Asia is addressed. The authors conducted present and future Asian regional climate simulations which were nested in the results of Atmospheric General Circulation Model （AGCM） experiments. The regional climate model could capture the general simulated features of the AGCM. Also, some regional phenomena such as orographic precipitation, which did not appear in the outcome of the AGCM simulation, were successfully produced. Under global warming, the increase of water vapor associated with the warmed air temperature was projected. It was projected to bring more abundant water vapor to the southern portions of India and the Bay of Bengal, and to enhance precipitation especially over the mountainous regions, the western part of India and the southern edge of the Tibetan Plateau. As a result of the changes in the synoptic flow patterns and precipitation under global warming, the increases of annual mean precipitation and surface runoff were projected in many regions of Asia. However, both the positive and negative changes of seasonal surface runoff were projected in some regions which will increase the flood risk and cause a mismatch between water demand and water availability in the agricul  相似文献   

Simultaneous MITSuME g'R_CI_C monitoring of S5 0716+714     

C. S. Stalin  Koji. S. Kawabata  Makoto Uemura  Michitoshi Yoshida  Nobuyuki Kawai  Kenshi Yanagisawa  Yasuhiro Shimizu  Daisuke Kuroda  Shogo Nagayama  Hiroyuki Toda 《Monthly notices of the Royal Astronomical Society》2009,399(3):1357-1366

  相似文献   

Effects of non‐uniform traction and specimen height in the direct shear test on stress and deformation in a rock fracture     

Ausama A. Giwelli  Koji Matsuki  Kiyotoshi Sakaguchi  Akihisa Kizaki 《国际地质力学数值与分析法杂志》2013,37(14):2186-2204

In the direct shear test (DST), an internal moment is distributed within the rock specimen by non‐coaxial shear loads applied to the specimen, which cause non‐uniform distributions of both the traction on the loading planes and the stress and deformation in the specimen. To examine the validity of the DST for a rock fracture and to clarify the effect of specimen height, both the stress and deformation in a fracture in the DST were analyzed for specimens with three different heights using a three‐dimensional finite element method with quadratic joint elements for a fracture model. The constitutive law of the fracture considers the dependence of the non‐linear behavior of closure on shear displacement and that of shear stiffness on normal stress and was implemented in simulation code to give a conceptional fracture with uniform mechanical properties to extract only the effect of non‐uniform traction on the stress and deformation in the fracture. The results showed that both normal and shear stresses are concentrated near the end edges of the fracture, and these stress concentrations decrease with a decrease in the specimen height according to the magnitude of the moment produced by the non‐coaxial shear loads. Furthermore, although closure is greater near the end edges of the fracture, where normal stress is concentrated, this concentration of closure is not so significant within the range of this study because of the non‐linear behavior of closure, that is, closure does not significantly increase with an increase in normal stress at large normal stresses. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Identification of Pathways for Hydrogen Gas Migration in Fault Zones with a Discontinuous,Heterogeneous Permeability Structure and the Relationship to Particle Size Distribution of Fault Materials     

Masakazu?NiwaEmail author  Hideki?Kurosawa  Koji?Shimada  Tsuneari?Ishimaru  Hideki?Kosaka 《Pure and Applied Geophysics》2011,168(5):887-900

Previous studies have reported that high concentrations of H₂ gas are released from active fault zones. Experimental studies suggest that the H₂ gas is derived from the reaction of water with free radicals formed when silicate minerals are fractured at hypocenter depths during fault activities. However, the pathways for migration of deep-seated fluids to surface are still unknown. In this study we performed quick, multipoint H₂ gas measurements across a fault zone using a portable gas monitor and a hand drill. The fault zone studied includes a smectite-rich fault core dividing two clearly distinguishable damage zones: granite cataclasite and welded tuff fault breccia. The measurements show that H₂ gas emissions collected in 2–3 h sampling periods from start of measurement range from 320.3 to 446.2 ppm/min in the granite cataclasite and 60.5 to 137.8 ppm/min in the welded tuff fault breccias. Negligible quantities of H₂ gas could be collected from the fault core. Particle size distribution analyses of fault rocks indicate that the granite cataclasite tends to be rich in particles that are finer, i.e., less cohesive and easy to disaggregate, which leads to the inference that the granite cataclasite has high permeability. Based on the H₂ gas measurements and the particle size distribution analyses, the H₂ gas is considered to have migrated in permeable damage zones mostly by advection with groundwater. Multipoint H₂ gas measurement will be effective in qualitative delineation of variations in permeability of regional structures.  相似文献   

Reciprocal sound transmission measurement of mean current and temperature variations in the central part (Aki-nada) of the Seto Inland Sea,Japan     

Yudi Adityawarman  Arata Kaneko  Koji Nakano  Naokazu Taniguchi  Katsuaki Komai  Xinyu Guo  Noriaki Gohda 《Journal of Oceanography》2011,67(2):173-182

A 30 km-range reciprocal sound transmission experiment was carried out on the line connecting Honshu and Shikoku (the first and fourth biggest main Japanese islands, respectively) in the central part (Aki-nada) of the Seto Inland Sea, Japan, during March–May 2010 to measure the mean current and temperature variations over the sea. The range-averaged current along the sound transmission line was estimated to have a mean and standard deviation of (3.8–4.4) ± (1.7–1.8) cm/s after converting the travel time difference data into currents, including a fortnightly tidal variation in the range of ±30 cm/s. The positive mean current implies slow water movement from the west to east through Aki-nada. The range-averaged speed of sound was estimated by converting from the mean travel time or one-way travel time into the speed of sound, and further converted into temperature for fixed values of salinity and depth, according to the standard speed of sound formula. Besides the precise measurement (to an accuracy of 0.01°C) of semidiurnal and diurnal tidal variations and seasonal warming, the temperature data showed periodic variations with periods of 7.0 and 21.1 days that had never been observed in Aki-nada before. This study suggests that reciprocal sound transmission is a powerful technique for the long-term accurate measurement of mean current and temperature variations in coastal and inland seas.  相似文献   

Measuring Flume Surfaces for Hydraulics Research Using a Kodak DCS460     

Jim H. Chandler  Koji Shiono  Ponnambalam Rameshwaren  & Stuart N. Lane 《The Photogrammetric Record》2001,17(97):39-61

A critical problem in hydraulics research is accurate measurement of fluvially worked sediments, both in the field and in scaled representations of field situations in laboratory flumes. Such measurement must provide information on individual grain characteristics, and their organisation into structures referred to as bedforms. Existing measurement approaches are based upon mechanical or laser profiling devices, which are both expensive and take considerable time to acquire data, particularly where information is required at very high densities. This paper demonstrates how conventional automated terrain model extraction software, combined with image acquisition using a Kodak DCS460 digital camera, has been effective in generating digital elevation models of complex bed morphology. This has reduced time spent collecting data in the flume and has allowed data collection at much higher spatial and temporal densities. Application of the method is illustrated by research carried out at Hydraulics Research Wallingford. Issues discussed include configuration of photographs and control coordinates; appropriate camera calibration methods; stability of inner orientation of the Kodak DCS460; and accuracies obtained. Comparisons with independent check data reveal that accuracies of ±2.5mm have been achieved using a camera-to-object distance of 4.2 m.  相似文献