Osaka Bay Research Articles

Expansion of blooming in the toxic dinoflagellate Alexandrium tamarense and environmental fluctuation analyzed from long-term monitoring data in Osaka Bay, eastern Seto Inland Sea, Japan

Expansion of blooming in the toxic dinoflagellate <i>Alexandrium tamarense</i> and environmental fluctuation analyzed from long-term monitoring data in Osaka Bay, eastern Seto Inland Sea, Japan

Morphology and distribution of juveniles of three cynoglossid fishes occurring in Osaka Bay from August to October

Morphology and distribution of juveniles of three cynoglossid fishes occurring in Osaka Bay from August to October

大阪湾で麻痺性貝毒により毒化したアカガイ，トリガイにおける毒量および毒成分の経時変化と種間の差異

大阪湾で麻痺性貝毒により毒化したアカガイ，トリガイにおける毒量および毒成分の経時変化と種間の差異

Osaka Bay in Japan as a model for investigating the factors controlling temporal and spatial persistence among introduced marine and brackish species in a heavily industrialized harbor

Osaka Bay in Japan as a model for investigating the factors controlling temporal and spatial persistence among introduced marine and brackish species in a heavily industrialized harbor

Distribution of Parent and Alkylated PAHs in Bivalves Collected from Osaka Bay, Japan

Distribution of Parent and Alkylated PAHs in Bivalves Collected from Osaka Bay, Japan

Distribution of perfluoroalkyl compounds in Osaka Bay and coastal waters of Western Japan

Perfluoroalkyl acids (PFAAs) including perfluoroalkyl sulfonates (PFSAs) and perfluoroalkyl carboxylates (PFCAs) were analyzed in sediment samples taken from Ajifu Waterway in Osaka city, from Osaka Bay, and from Kagoshima Bay, as well as in fifteen seawater samples collected from Osaka Bay and coastal waters of Western Japan. In all sediment samples, only PFCAs were detected, and the highest concentration was determined in Ajifu Waterway, where ΣPFAA was 58990 ng kg−1 dry weight. The total concentrations of PFAAs in sea water samples ranged between the limit of quantification and 53.4 ng L−1, and perfluorohexanoic acid was the most prevalent and had the highest concentration of 37 ng L−1. The changes in the patterns and concentrations of PFAAs in Osaka Bay and coastal waters of Western Japan indicate that the PFAAs in surface waters are influenced by sources from Keihanshin Metropolitan Area, mainly the Yodo River basin, and the dilution effect which naturally occurs during their transport to the Pacific Ocean.

Estimation of oil overflow due to sloshing from oil storage tanks subjected to a possible Nankai Trough earthquake in Osaka bay area

Sloshing of oil storage tanks is a great threat to industrial complexes when huge earthquakes occur. Overflow of oil due to sloshing could lead to serious tank fire and to oil dispersion due to Tsunamis. Since liquid sloshing is characterized as a highly nonlinear free-surface flow, numerical approaches are more suitable than theoretical ones to estimate the overflow from oil storage tanks caused by sloshing. The moving particle simulation (MPS) method, which is a mesh-free and Lagrangian particle method, is applied to the sloshing simulation. Thanks to the perfect mass conservation of the particle method, the overflow amount of oil can be accurately estimated by simply counting the number of overflowed fluid particles.There is high-possibility of occurrence of huge earthquakes along the Nankai Trough subduction zone, and the worst scenario is presumed as MW9.0, which is the same as the 2011 Tohoku earthquake. In order to simulate sloshing of oil storage tanks subjected to a possible Nankai Trough earthquake, ground shaking characteristics of the site need to be evaluated. Therefore we carried out microtremor measurements with high density in an industrial complex in Osaka bay area. A strong ground motion during a scenario earthquake with MW9.0 along the Nankai Trough is estimated based on the SMGA models considering the empirical site amplification and phase effects.Fully nonlinear sloshing simulations, using an in-house GPU computing code based on the explicit MPS method, are performed for a large-size oil storage tank installed with a floating roof by imposing the estimated strong ground motion of Nankai Trough earthquake as the external oscillation. As a result, significant amount of oil flows onto the floating roof and large amount of oil overflow from the tank is confirmed. The numerical result suggests the entire fire is one of major concerns for the assumed earthquake scenario. Finally sloshing simulations are repeated for small- and medium-size tanks, and then the total amount of outflow oil is estimated for the industrial complex of interest in the estimated Nankai Trough earthquake.

Brief sea‐level fall event and centennial to millennial sea‐level variations during Marine Isotope Stage 19 in Osaka Bay, Japan

ABSTRACTDetailed sea‐level variation was investigated for Marine Isotope Stage (MIS) 19, based on diatom and grain size analyses of a marine sequence in a core of the Osaka Group. Diatom sea‐level proxies represent precession‐related signals correlated with highstands MIS 19.3 and 19.1, and lowstand MIS 19.2. Astronomical tuning shows the marine sequence has a uniform accumulation rate of about 60 cm ka−1. A rapid sea‐level fall event was found in the earliest MIS 19, demonstrated by several independent sea‐level proxies of diatom and grain size. This event began with a rapid sea‐level drop, followed by a gradual recovery, at about 783–782 ka. A maximum abundance of pelagic diatom taxa at a core depth of 402.20 m evidently shows the highest sea‐level peak in MIS 19, supported by many other proxies. Based on the diatom data, sea‐level change across MIS 19.1 is characterized by centennial to millennial fluctuations. The sea‐level fall event began just after the onset of a cooling event previously reported from the same core. Observations of a comparable sea‐level fall signal in many deep‐sea core records suggest the event is global.

Isotach Elastoplasticity: A Case Study on Osaka Bay Clay

The theory of isotach elastoplasticity (IEP) is applied to investigate the strain rate and time effects in Osaka Bay clay from Japan. The IEP theory considers geomaterials like clays as an overdamped oscillatory physical system, for which the strain rate (analogous to the vibration frequency) decays in an exponential manner. This feature can be captured by a characteristic strain rate and time relationship. The evolutionary change of strain rate is found to affect the mechanical response of soft clays in an isotach manner. A loading–isotach (LI) yield curve is proposed in the stress and strain rate plane. Combination of the characteristic strain rate and time relationship in an isotach manner into the framework of critical state soil mechanics renders an isotach (rate-dependent) elastoplastic (IEP) constitutive model. A total of 9 model parameters is required, and their values can be properly determined via conventional laboratory tests. The validity of the proposed IEP is demonstrated using experimental data for Osaka Bay clay under various stress paths and strain rates, namely, long-term creep, constant rate of strain loading, relaxation, and their combination. Comparison of the model predictions and experimental results demonstrates that the theory of isotach elastoplasticity can be successfully applied to capture the strain rate and time effects on the mechanical behaviour of Osaka Bay clay.

DISASTER PREVENTION COASTAL MAP PRODUCTION BY MMS &amp; C3D

Abstract. In March 2011, Eastern Japan suffered serious damage of Tsunami caused by a massive earthquake. In 2012, Ministry of Land, Infrastructure and Transport published “Guideline of setting assumed areas of inundation by Tsunami” to establish the conditions of topography data used for simulation of Tsunami. In this guideline, the elevation data prepared by Geographical Survey Institute of Japan and 2m/5m/10m mesh data of NSDI are adopted for land area, while 500m mesh data of Hydrographic and Oceanographic Department of Japan Coast Guard and sea charts are adopted for water area. These data, however, do not have continuity between land area and water area. Therefore, in order to study the possibility of providing information for coastal disaster prevention, we have developed an efficient method to acquire continuous topography over land and water including tidal zone. Land area data are collected by Mobile Mapping System (MMS) and water area depth data are collected by interferometry echo sounder (C3D), and both data are simultaneously acquired on a same boat. Elaborate point cloud data of 1m or smaller are expected to be used for realistic simulation of Tsunami waves going upstream around shoreline. Tests were made in Tokyo Bay (in 2014) and Osaka Bay (in 2015). The purpose the test in Osaka Bay is to make coastal map for disaster prevention as a countermeasure for predicted Nankai massive earthquake. In addition to Tsunami simulation, the continuous data covering land and marine areas are expected to be used effectively for maintenance and repair of aged port and river facilities, maintenance and investigation of dykes, and ecosystem preservation.

일본 후쿠시마 근해에서 방출된 오염물질에 미치는 태풍의 영향

We examined the diffusion of contaminants released from the southern coast around Fukushima, Japan, during the passage of typhoons using a three-dimensional numerical model (POM) to track diffusing radioactivity (RA) released from the nuclear power plant at Fukushima following the accident caused by the giant tsunami event in March 2011. Radioactive contaminants released during the passage of typhoons may have significantly affected not only Japanese but also Korean coastal waters. The model domain covered most of the northwestern Pacific including marginal seas such as the East/Japan Sea and the Yellow Sea. Several numerical experiments were conducted case studies focusing on the westward diffusion from the southern coast of Japan of contaminants derived from the source site (Fukushima) according to various attributes of the typhoons, such as intensity, track, etc. The model produced the following results 1) significant amounts of contaminants were transported in a westward direction by easterly winds favorable for generating a coastal air stream along the southern Japanese coast, 2) the contaminants reached as far as Osaka Bay with the passage of typhoons, forced by a 5-day positive sinusoidal form with a (right-) northward track east of Fukushima, and 3) the range of contamination was significant, extending to the interior of the East/Japan Sea around the Tsugaru Strait. The model suggests that contaminants and/or radioactivity released from Fukushima with the passage of typhoons can affect Korean waters including the northeastern East/Japan Sea around the Tsugaru Strait, especially when the typhoon tracks are favorable for generating a westward coastal air stream along the southern Japanese coast.

A cooling event during the last interglacial period from pollen analysis of an Osaka Bay core

A cooling event during the last interglacial period from pollen analysis of an Osaka Bay core

Key biogeochemical processes evaluated by the stable nitrogen isotopes of dissolved inorganic nitrogen in the Yodo River estuary, Japan: significance of estuarine nutrient recycling as a possible source for coastal production

Isotope analysis of dissolved inorganic nitrogen (DIN) and a mixing model along the salinity gradient were used to clarify the dominant biogeochemical processes controlling nutrient dynamics within a shallow eutrophic estuary in Japan. Although delivery of riverine DIN into the estuary is largely dominated by mixing with seawater during most months, internal biogeochemical processes of DIN assimilation by phytoplankton and DIN production by remineralization and subsequent nitrification within the estuary offer the most reasonable explanation for observed deviations in the isotopic compositions of $$ {\text{NO}}_{3}^{ - } $$ from mixing behavior. However, the balance of each process changed over time. During phytoplankton blooming in summer, co-occurrence of $$ {\text{NO}}_{3}^{ - } $$ assimilation and $$ {\text{NO}}_{3}^{ - } $$ regeneration inhibited the accumulation of $$ {\text{NO}}_{3}^{ - } $$ within the estuary. Moreover, assimilation of $$ {\text{NH}}_{4}^{ + } $$ as well as $$ {\text{NO}}_{3}^{ - } $$ by phytoplankton complicates the nutrient dynamics within the estuary. However, mostly conservative or productive behavior of DIN as well as $$ {\text{PO}}_{4}^{3 - } $$ showed that recycled nutrients are significant net source within the estuary. These results suggest recycled nutrients within the estuary could have a non-negligible impact on eutrophication in Osaka Bay.

Closure to “Settlement of the Kansai International Airport Islands” by G. Mesri and J. R. Funk

Closure to “Settlement of the Kansai International Airport Islands” by G. Mesri and J. R. Funk

大阪湾における底層貧酸素の変動特性と持続時間

大阪湾をはじめとする閉鎖性海域では, 夏季の底層水の貧酸素化が問題となっている。貧酸素が環境や底生生物に与える影響には, 貧酸素の持続時間が重要な指標となる。国土交通省近畿地方整備局が公開している大阪湾水質定点自動観測データ配信システムの毎時データを用いて, 大阪湾の底層貧酸素の変動状況及び貧酸素状態の持続時間を2011年から2013年まで整理した。その結果, 多くの地点で夏季の底層DO (溶存酸素) の日変動幅は平均1 mg L-1以上, 月内での標準偏差は1 mg L-1以上を示した。大阪湾南東側の地点では, 強風時に貧酸素から回復する事例が多くみられ, 貧酸素が最も強くなる8月を除き, 貧酸素状態から頻繁に回復し, 貧酸素の持続時間は24時間未満となることが多かった。一方, 大阪湾北側の地点では, 強風に対する応答が南東側の地点より弱く, 貧酸素の持続時間も長い傾向にあった。

222Rnを用いた大阪湾における地下水湧出現象の調査解析

Recent studies have reported that submarine groundwater discharge (SGD) is not negligible as a nutrient source from land to coastal sea. In order to evaluate SGD rate and its influence on water quality of sea bottom water in Osaka Bay, field surveys and analyses were conducted utilizing 222Rn as a natural tracer. As the results, 222Rn concentration represented the higher value in the bay head than the offshore. Principal component analysis indicated that the water quality of bottom layer in the north port area was affected by SGD. Moreover, numerical analyses showed that 222Rn flux from the sea bottom was estimated at 0 to 120 Bq/m2/day and that local flow field and estuary circulation played an important role in 222Rn distribution in the bay.

大阪湾における底質環境とマクロベントス群集—2003 年と 2011 年

大阪湾における底質環境とマクロベントス群集—2003 年と 2011 年

A New Risk Evaluation Model for Safety Management on an Entire Ship Route

In this paper, the authors introduce a new risk evaluation model for evaluating the navigation safety zone for an entire ship route. This model considers a new algorithm to determine the navigational safety zone in real-time, and also takes the navigation officers’ perception while navigating a ship into consideration. The risk quantification has been developed using a questionnaire and incorporated into the new model. A simulation was carried out for the Osaka bay area in order to verify the usefulness of the proposed model. A new approach was employed to monitor the level of navigation safety along a ship route. The entire ship route is divided into small sections as a gridded matrix. The level of navigation safety can be quantified by means of a safety index on the basis of the ship’s navigation data within a specified distance range. The results show that the comparison between risks identified for different sections across the entire ship route is easy, which helps determine the navigational safety zone quickly. This model is expected to be able to serve as a new tool for managing safety throughout an entire ship route area in real-time in order to support the port safety authority or vessel traffic service center.

大阪地域における夏季夜間の風系パターンと気温の関係

Since Osaka plain faces the Osaka bay, land and sea breezes tend to develop there. To reveal the relationship between the land and sea breezes and air temperature in summer night, we classified the wind systems in Osaka area by using a cluster analysis and examined the relationship between each wind pattern and air temperature distribution. The result shows that sea breezes at night make air temperature higher in Osaka area. When a land breeze develops, the occurrence of a land breeze is relevant to a decrease of air temperature.

Origin of NOx emission from ships inside major bays in Japan

The amount of NOx emission from ships inside the major bays in Japan, i.e., Tokyo Bay, Osaka Bay and Ise Bay, are analyzed and the strategies in the reduction of NOx emission are discussed. Normally each ship has three sources of NOx emission, i.e., main engine, auxiliary engine and auxiliary boiler. Since wide range of ships are in operation in these bays, each of the ships are categorized in 4 ranks by the size of each ships. The amounts of NOx emission from each source and each rank of ships are estimated separately and compared with each other to understand the origin of NOx emission inside these bays. From the systematic calculations, it was explored that more than half of the amount of NOx was emitted from the auxiliary engines during the anchorage period. Especially the influence of the NOx emission from auxiliary engines of larger sized ships of rank 4, the largest category, is the largest. This should be mainly due to the longer anchorage and cargo work time necessary for handling the larger amount of cargo of larger sized ships. On the other hand the NOx emission from main engines is mainly emitted from the small sized ships of rank 1. Same tendencies are obtained through the NOx emission calculations of three major bays in Japan. From these results, it is suggested that the usage of land electricity in larger sized ships is effective in the reduction of NOx emission in major bays.