Impact of flood events on macrobenthic community structure on an intertidal flat developing in the Ohta River Estuary     

Wataru Nishijima  Yoichi Nakano  Satoshi Nakai  Tetsuji Okuda  Tsuyoshi Imai  Mitsumasa Okada 《Marine pollution bulletin》2013

We investigated the effects of river floods on the macrobenthic community of the intertidal flat in the Ohta River Estuary, Japan, from 2005 to 2010. Sediment erosion by flood events ranged from about 2–3 cm to 12 cm, and the salinity dropped to 0‰ even during low-intensity flood events. Cluster analysis of the macrobenthic population showed that the community structure was controlled by the physical disturbance, decreased salinity, or both. The opportunistic polychaete Capitella sp. was the most dominant species in all clusters, and populations of the long-lived polychaete Ceratonereis erythraeensis increased in years with stable flow and almost disappeared in years with intense flooding. The bivalve Musculista senhousia was also an important opportunistic species that formed mats in summer of the stable years and influenced the structure of the macrobenthic community. Our results demonstrate the substantial effects of flood events on the macrobenthic community structure.  相似文献   

应用BOLD进行核磁脑功能成像的误区：神经元活动时脑血氧变化的多样性     

酒谷  薰博士  Chikashi Fukaya 《CT理论与应用研究》2000,9(Z1):125-126

Functional MRI (fMRI) is recognized as a well-established non-invasive diagnostic method to image activating cortical areas. Currently, the blood oxygenation level dependent (BOLD) contrast method is widely used in fMRI. BOLD-fMRI images activating are as by detecting a reduced concentration of deoxyhemoglobin during neuronal activity, which is caused by a larger increase in O2 delivery compared with O2 consumption in normal adults. In the present study, near infrared spectroscopy, which is an optical method to evaluate cerebral blood oxygenation changes, has demonstrated an increase of deoxyhcmoglobin associated with increases of oxyhemoglobin and total hemoglobin at activation areas of stroke patients, whereas BOLD-fMRI failed to image the activation areas. The present findings have serious implications for the appiication of BOLD-fMRI to the patients with brain disorders because BOLD-fMRI may overlook neuronal activities in these patients unless both increases and decreases of signals are considered.  相似文献   

Effects of mass source/sink at the western boundary on the wind-driven gyres: Implications for the ventilation of the north pacific intermediate layer through convection in the Okhotsk Sea and tidal mixing at the Kuril Straits     

Tomohiro Nakamura  Takahiro Toyoda  Yoichi Ishikawa  Toshiyuki Awaji 《Journal of Oceanography》2010,66(1):41-60

A steady quasi-geostrophic 2.5-layer model, forced by both Ekman pumping and a mass source/sink situated at the western boundary has been constructed to investigate the effect of diapycnal transport due to convection in the Okhotsk Sea and tidal mixing at the Kuril Straits on the intermediate layer in the North Pacific. The model illustrates a combined effect of the wind-driven and mass-driven circulations. First, net mass input induces a “barotropic” mode inter-gyre flow along the western boundary through the dynamical influence of Kelvin waves. This flow creates characteristic curves (geostrophic contours) that facilitate inter-gyre communication through the western boundary layer from the location of the mass source to the subtropical gyre. Due to the effect of wind-driven circulation, the offshore part turns eastward into the interior, encircles the outer rim of the region (which would otherwise be the pool region in the absence of mass input), and then encounters the western boundary. Eventually, the water fed into the lower layer flows mostly along this path and later flows away to the equatorial region. Conversely, in the upper layer, water is fed from the equator to the subtropics, and to the subpolar interior region through the western boundary current. The water then circulates along the outer rim and is absorbed into the mass sink. The model is controlled mainly by three nondimensional parameters: (1) the ratio of net mass input rate to the maximum Sverdrup transport (Q/T _Sv ^max ), which affects the inter-gyre communication by altering the paths of geostrophic contours, (2) the ratio of a mass input rate into the lower layer to that in total (Q ₂/Q), which controls the vertical structure of the inter-gyre flow, and (3) the measure of the wind forcing effect relative to the β effect, which determines the horizontal extent of the area influenced by the mass input. The other parameter regimes with respect to Q/T _Sv ^max and Q ₂/Q are also presented.  相似文献   

Impact of in-consistency between the climate model and its initial conditions on climate prediction     

Liu  Xueyuan  Köhl  Armin  Stammer  Detlef  Masuda  Shuhei  Ishikawa  Yoichi  Mochizuki  Takashi 《Climate Dynamics》2017,49(3):1061-1075

We investigated the influence of dynamical in-consistency of initial conditions on the predictive skill of decadal climate predictions. The investigation builds on the fully coupled global model “Coupled GCM for Earth Simulator” (CFES). In two separate experiments, the ocean component of the coupled model is full-field initialized with two different initial fields from either the same coupled model CFES or the GECCO2 Ocean Synthesis while the atmosphere is initialized from CFES in both cases. Differences between both experiments show that higher SST forecast skill is obtained when initializing with coupled data assimilation initial conditions (CIH) instead of those from GECCO2 (GIH), with the most significant difference in skill obtained over the tropical Pacific at lead year one. High predictive skill of SST over the tropical Pacific seen in CIH reflects the good reproduction of El Niño events at lead year one. In contrast, GIH produces additional erroneous El Niño events. The tropical Pacific skill differences between both runs can be rationalized in terms of the zonal momentum balance between the wind stress and pressure gradient force, which characterizes the upper equatorial Pacific. In GIH, the differences between the oceanic and atmospheric state at initial time leads to imbalance between the zonal wind stress and pressure gradient force over the equatorial Pacific, which leads to the additional pseudo El Niño events and explains reduced predictive skill. The balance can be reestablished if anomaly initialization strategy is applied with GECCO2 initial conditions and improved predictive skill in the tropical Pacific is observed at lead year one. However, initializing the coupled model with self-consistent initial conditions leads to the highest skill of climate prediction in the tropical Pacific by preserving the momentum balance between zonal wind stress and pressure gradient force along the equatorial Pacific.

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Tidal Mixing in the Kuril Straits and Its Impact on Ventilation in the North Pacific Ocean     

Tomohiro Nakamura  Takahiro Toyoda  Yoichi Ishikawa  Toshiyuki Awaji 《Journal of Oceanography》2004,60(2):411-423

A numerical study using a 3-D nonhydrostatic model has been applied to baroclinic processes generated by the K ₁ tidal flow in and around the Kuril Straits. The result shows that large-amplitude unsteady lee waves are generated and cause intense diapycnal mixing all along the Kuril Island Chain to levels of a maximum diapycnal diffusivity exceeding 10³ cm²s⁻¹. Significant water transformation by the vigorous mixing in shallow regions produces the distinct density and potential vorticity (PV) fronts along the Island Chain. The pinched-off eddies that arise and move away from the fronts have the ability to transport a large amount of mixed water (∼14 Sv) to the offshore regions, roughly half being directed to the North Pacific. These features are consistent with recent satellite imagery and in-situ observations, suggesting that diapycnal mixing within the vicinity of the Kuril Islands has a greater impact than was previously supposed on the Okhotsk Sea and the North Pacific. To examine this influence of tidal processes at the Kurils on circulations in the neighboring two basins, another numerical experiment was conducted using an ocean general circulation model with inclusion of tidal mixing along the islands, which gives a better representation of the Okhotsk Sea Mode Water than in the case without the tidal mixing. This is mainly attributed to the added effect of a significant upward salt flux into the surface layer due to tidal mixing in the Kuril Straits, which is subsequently transported to the interior region of the Okhotsk Sea. With a saline flux into the surface layer, cooling in winter in the northern part of the Okhotsk Sea can produce heavier water and thus enhance subduction, which is capable of reproducing a realistic Okhotsk Sea Mode Water. The associated low PV flux from the Kuril Straits to the open North Pacific excites the 2nd baroclinic-mode Kelvin and Rossby waves in addition to the 1st mode. Interestingly, the meridional overturning in the North Pacific is strengthened as a result of the dynamical adjustment caused by these waves, leading to a more realistic reproduction of the North Pacific Intermediate Water (NPIW) than in the case without tidal mixing. Accordingly, the joint effect of tidally-induced transport and transformation dominating in the Kuril Straits and subsequent eddy-transport is considered to play an important role in the ventilation of both the Okhotsk Sea and the North Pacific Ocean. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Application of Sensitivity Analysis Using an Adjoint Model for Short-Range Forecasts of the Kuroshio Path South of Japan     

Yoichi Ishikawa  Toshiyuki Awaji  Nobumasa Komori  Takahiro Toyoda 《Journal of Oceanography》2004,60(2):293-301

A sensitivity experiment has been performed by assimilating altimetric data into a 1.5-layer primitive equation model as a first attempt to examine the impact of initialization on forecasts of the Kuroshio path variability south of Japan. By exploiting the advantage of an adjoint model, our approach clearly shows that a small meander off Shikoku Island has a large impact on the prediction of meander growth in the Kuroshio region. Further, the strengthening of the Kuroshio current and its recirculation clearly becomes an important factor in the development of the meander. These results demonstrate the effectiveness of our assimilation approach in identifying efficient initialization schemes on numerical forecasting of the Kuroshio south of Japan and should help in the construction of an effective observing system for improving the forecasting. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Rapid and frequent turbidite accumulation in the bottom of Izu-Ogasawara Trench: Chemical and radiochemical evidence   总被引：1，自引：0，他引：1  

Yoshiyuki Nozaki  Yoichi Ohta 《Earth and Planetary Science Letters》1993,120(3-4):345-360

Two sediment cores (pilot gravity and piston) were obtained from the bottom of the Izu-Ogasawara Trench at 9750 m and analyzed for various elements and radioisotopes. The results showed a history of complex and frequent turbidite deposition: In the gravity core, eight layers rich in manganese were observed, of which five are enriched in Cu and Co as well. The other three are also enriched in Mo but no other heavy metals, suggesting the presence of at least two mechanisms of formation. Trapping of iron manganese micronodules can account for the enrichment of Mn, Cu and Co. The other three layers rich in Mn and Mo appear to be formed by a post-depositional diagenetic process of Mn mobilization and redeposition in the sediment column. A strong correlation between ²²⁶Ra and Cu in the gravity core suggests that the ²²⁶Ra was also carried into the bottom of the trench in turbidites in association with Mn micronodules. Little excess of ²¹⁰Pb over ²²⁶Ra was found at the top but the excess was significant at mid-depths from 30 to 70 cm, indicating that those sediments were deposited within the last 200 y.

In the piston core there is a sharp discontinuity of chemical and radiochemical composition around a depth of 250 cm. Below that depth the sediments appear to be dominated by materials derived from terrestrial sources, as compared with those in the upper layer which are of contemporary marine origin. ²²⁶Ra is deficient relative to ²³⁰Th throughout the sediment column down to 6 m. This finding is consistent with the finding that the average rate of sediment accumulation is 1–2 orders of magnitude faster than that in the western North Pacific abyssal plain, suggesting the convergence of materials into the bottom of the trench.  相似文献   

A fluidized landslide on a natural slope by artificial rainfall   总被引：9，自引：5，他引：4  

Hirotaka?Ochiai  Yasuhiko?OkadaEmail author  Gen?Furuya  Yoichi?Okura  Takuro?Matsui  Toshiaki?Sammori  Tomomi?Terajima  Kyoji?Sassa 《Landslides》2004,1(3):211-219

An experiment to induce a fluidized landslide by artificial rainfall was conducted on a natural slope at Mt. Kaba-san in the village of Yamato, Ibaraki Prefecture, Japan. The experimental slope was 30 m long, 5 m wide, and the average slope gradient was 33°. A landslide initiated 24,627.5 s (410 m/27.5 s) after the start of sprinkling at a rainfall intensity of 78 mm/h. The landslide mass was 14 m long and 1.2 m deep (at maximum). It first slid, then fluidized, and changed into a debris flow. The travel distance was up to 50 m in 17s. The apparent friction angle of the fluidized landslide was 16.7°. Formation of the sliding surface was detected by soil-strain probes. Motion of the surface of the failed landslide mass was determined by stereo photogrammetry.  相似文献   

Superconducting gravimeter observations without a tilt compensation system     

Sachiko Iwano  Yoichi Fukuda 《Physics of the Earth and Planetary Interiors》2004,147(4):343-351

This paper examines the possibility of using superconducting gravimeter (SG) observations without a tilt compensation system. SG data obtained at Syowa Station, Antarctica, were recorded without tilt compensation from April 5, 2001 to January 4, 2002, however, tilt signals were registered during this time period. A tilt correction was applied to gravity data from August 2, 2001 to January 4, 2002. After the tilt correction, errors of tidal parameters were dramatically reduced and tidal parameters themselves almost coincide with those from the same length of tilt-controlled gravity data recorded in 2000, when tilt compensation system was used. The noise level of the thermal leveler in the seismic band was also investigated. Averaged power spectra of gravity from 15 quiet days each in 2000 and 2001 recorded with and without the tilt compensation system, respectively, were compared. ‘Quiet’ in this case, means very low earthquake activity and calm wind conditions. No significant difference in the seismic band, except at the frequency of 2 mHz, was noticed. The difference at 2 mHz occurred because of room temperature variations caused by the water cooler, which cools down a compressor by automatically switching on and off.  相似文献   

A geophysical interpretation of the secular displacement and gravity rates observed at Ny-Ålesund, Svalbard in the Arctic—effects of post-glacial rebound and present-day ice melting     

Tadahiro Sato  Jun'ichi Okuno  Jacques Hinderer  Daniel S. MacMillan  Hans-Peter Plag †  Olivier Francis ‡  Reinhard Falk  Yoichi Fukuda 《Geophysical Journal International》2006,165(3):729-743

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