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The residual currents in Tokyo Bay during four seasons are calculated diagnostically from the observed water temperature, salinity and wind data collected by Unokiet al. (1980). The calculated residual currents, verified by the observed ones, show an obvious seasonal variable character. During spring, a clear anticlockwise circulation develops in t...
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... In previous studies (2015unpublished), comparisons with other eelgrass bed (Ikuno-shima Is., Nanao Bay, and Mutsu Bay) around Japan, Futtsu showed a faster tidal flow. Guo and Yanagi (1996) also demonstrated strong residual currents in the middle of Tokyo Bay. In this area, some anthropogenic disturbance, such as raking for clams by local fisherman, was constantly observed (Yamakita et al., 2011). ...
Zostera marina (eelgrass) is classified as one of the marine angiosperms and is widely distributed throughout much of the Northern Hemisphere. The present study investigated the microbial community structure and diversity of Z. marina growing in Futtsu bathing water, Chiba prefecture, Japan. The purpose of this study was to provide new insight into the colonization of eelgrass leaves by microbial communities based on leaf age and to compare these communities to the root-rhizome of Z. marina, and the surrounding microenvironments (suspended particles, seawater, and sediment). The microbial composition of each sample was analyzed using 16S ribosomal gene amplicon sequencing. Each sample type was found to have a unique microbial community structure. Leaf-attached microbes changed in their composition depending on the relative age of the eelgrass leaf. Special attention was given to a potential microbial source of leaf-attached microbes. Microbial communities of marine particles looked more like those of eelgrass leaves than those of water samples. This finding suggests that leaf-attached microbes were derived from suspended particles, which could allow them to go back and forth between eelgrass leaves and the water column.
... The area north of the line connecting those two points is very shallow, with an average depth of 17 m (hereafter, the inner bay). In the inner bay, salinity is low throughout the year due to large river inflows (Guo and Yanagi 1996). The outer bay (south of the line to another line between Sunosaki point to Tsurugizaki point), in contrast, faces the open ocean and Sagami Bay, where the bottom depth drops sharply from 70 to 900 m in the southward direction. ...
The estimated biomass of mesopelagic fishes has been revised recently, indicating the importance of their roles in oceanic ecosystems and global biogeochemical cycling. This study clarified the occurrence patterns of larval mesopelagic fish species in the surface layers of the highly eutrophic Tokyo Bay. Oceanographic observations and larval fish sampling were conducted across four seasons in 2003 and 2005–06 from the inner area to the mouth of the bay. The number of mesopelagic fishes sampled was 2,276 individuals of 78 species (14 families), accounting for 0.4% of total specimens and 25.4% of the total species number. Myctophidae comprised the largest number of species, with 43 species/morphotypes, followed by Gonostomatidae (seven species). Most larvae in Tokyo Bay were found to belong to tropical/subtropical species. The number of mesopelagic species was negatively correlated with the distance from the Kuroshio Current axis to the mouth of the bay, suggesting that these species were transported by the Kuroshio Current. A thermohaline front likely functions as a barrier preventing mesopelagic fish larvae from entering the inner bay area. Species in the outer bay and mouth of the bay clearly differed, likely due to the differing vertical distributions innate to each species. On the other hand, some species occurred in surface layers penetrated by inner bay water. In addition, the abundances of a myctophid species and copepods, which are potential food items for larvae, were positively correlated, suggesting that some mesopelagic larvae actively approach productive coastal waters due to the advantage of food availability.
... Although the 1st layer at site E7 on the east side is where the tidal mean was found directed toward the ocean (Figure 3a), it is quite possible that the water mass becomes an oceanic environment owing to the great and frequent inflow from the ocean (Figure 5a). This variability might be caused by variation in river discharge (Guo and Yanagi 1998), wind-induced currents in the bay (Guo and Yanagi 1996;Nakayama et al. 2014), penetration of oceanic water into the bay (Yanagi and Hinata 2004), and interaction between the penetration and the Coriolis force at the bay mouth (Nagashima and Okazaki 1979;Yagi et al. 2003). ...
Current patterns at the mouth of Tokyo Bay have been observed since the 1970s. However, earlier studies using short-term observations and numerical analyses were too limited in their spatiotemporal scale. This study analyzed long-term observations (over a decade) obtained using an acoustic Doppler current profiler mounted on a ferry that crosses the mouth of the bay. This long-term observation dataset revealed that tidal currents dominated at the bay mouth, and that an estuarine circulation of residual current was associated with inflow into the bay along topographic pathways formed by the Tokyo Submarine Canyon and the Uraga Channel. The water volume of the inflow was substantially greater than the discharge of the four major rivers flowing into Tokyo Bay. Although the mean residual current of the surface layer on the east side was outflow, it was variable with substantial and frequent inflow from the ocean, which might have caused an oceanic environment on the east side. Analysis of the long-term observations elucidated the spatial mean picture and temporal variability of the current patterns at the mouth of Tokyo Bay. This improved knowledge and the extended dataset will help answer remaining questions regarding the water quality in Tokyo Bay.
... The residual current also enhances the accumulation of organic matter in the inner bay. Several studies have indicated that the residual current in the inner bay, a horizontal anticlockwise circulation driven by wind curl stress that often develops in the head region of the bay has a large influence on the mass transport of particulate matter (Nakayama et al. 2014;Guo and Yanagi 1996). The center of this circulation is located at a latitude of 35.56° and moves longitudinally to 139.85° ~ 140.00° because of the average wind velocity in the SE-NW direction (Suzuki et al. 2012), which coincides with areas that have the highest TOC content, as shown in Figure 3. ...
Hypoxia and blue tide are the most significant environmental issues in Tokyo Bay as they have been damaging fisheries for a long time. Although studies on modeling these two associated phenomena have been conducted for decades, the scarcity of relevant observational datasets has greatly hindered the progress, and no study has successfully reproduced the entire processes of blue tide or predicted the time and place of its outbreak. To address the problems from limited data, this study proposed a relatively conventional benthic flux model and developed a novel method that converts the total organic carbon content into the fluxes of sediment oxygen consumption and sulfide release to represent the spatial differences in benthic fluxes. A pelagic sulfur model with only three key chemical reactions of blue tide that includes the disproportionation of elemental sulfur was proposed. The method significantly improved the results of dissolved oxygen in bottom water, as seen by the root mean square error decreasing by 15.9% and 18.9% in two simulations with largely different forcings. The sulfur model also accurately predicted the outbreaks of blue tides in each simulation, which is significant to the stakeholders as it facilitates the forecast of blue tides in Tokyo Bay.
... Since dead leaves decay and immediately get buried, a certain level of similarity may exist in microbial compositions between leaves laying above the sediment and in the bottom sediment just underneath. Based on these results, torn-off dead leaves may not be embedded in the bottom sediment, they appear to be transported out of the eelgrass bed by wind and residual currents unique the central part of Tokyo Bay (Guo and Yanagi, 1996). In previous studies (2015; unpublished), the physical and chemical properties of the following domestic eelgrass meadows were examined: Futtsu, Takehara (Ikuno-shima Is.), Nanao Bay, and Mutsu Bay (Table S4). ...
... In comparisons with other eelgrass meadows, Futtsu possessed a low-carbon and higher granular sediment, which implies its unique condition, namely, leaf litter is easily transported away by wind and/or water currents (Fig. S4). Guo and Yanagi (1996) showed the formation of residual currents in Tokyo Bay during the four seasons. Winddriven and tide-induced residual currents were calculated from hydraulic-observed data. ...
... Winddriven and tide-induced residual currents were calculated from hydraulic-observed data. They found that the north bank of Futtsu-Misaki was washed and swept by a clockwise circulation, the flow velocity of which may peak at approximately 5 cm/s (Guo and Yanagi, 1996;Tanaka, 2001). Strong residual currents in the middle of Tokyo Bay, as demonstrated by Guo and Yanagi (1996), are one of the transport mechanisms dispersing decayed leaves or suspended particles to surrounding water areas. ...
Zostera marina (eelgrass) is a widespread seagrass species that forms diverse and productive habitats along coast lines throughout much of the northern hemisphere. The present study investigated the microbial consortia of Z. marina growing at Futtsu clam-digging beach, Chiba prefecture, Japan. The following environmental samples were collected: sediment, seawater, plant leaves, and the root-rhizome. Sediment and seawater samples were obtained from three sampling points: inside, outside, and at the marginal point of the eelgrass bed. The microbial composition of each sample was analyzed using 16S ribosomal gene amplicon sequencing. Microbial communities on the dead (withered) leaf surface markedly differed from those in sediment, but were similar to those in seawater. Eelgrass leaves and surrounding seawater were dominated by the bacterial taxa Rhodobacterales (Alphaproteobacteria), whereas Rhodobacterales were a minor group in eelgrass sediment. Additionally, we speculated that the order Sphingomonadales (Alphaproteobacteria) acts as a major degrader during the decomposition process and constantly degrades eelgrass leaves, which then spread into the surrounding seawater. Withered eelgrass leaves did not accumulate on the surface sediment because they were transported out of the eelgrass bed by wind and residual currents unique to the central part of Tokyo Bay.
... Both field observations and numerical modeling have been applied to the study area (Dube et al., 1995;Goodrich et al., 1987;Guo and Valle-Levinson, 2008;Imasato, 1983;Zhai, Sheng, and Greatbatch, 2008). Some research has focused on the mechanism associated with local residual currents (Cai, Huang, and Long, 2003;Foreman et al., 2006;Guo and Yanagi, 1996;Kashiwai, 1984), although there has not been much work conducted on the west coast of Anmyeon-do; previous studies focused mainly on the Chunsu Bay area (Choi, 2004;Jung, Ro, and Kim, 2013a,b;Jung et al., 2015;Ro and Choi, 2004). ...
... Research on residual flows in bay waters has shown that residual flows are formed by lagrangian residual currents which form eddies that vary with the seasons [8,10]. Increasing the tidal amplitude at the open boundary significantly causes the residual flow regime to become more complicated at the bay, the effect of bottom friction on the residual current is relatively weak compared to the tidal effect [11]. ...
Research has been carried out to model current patterns and residual current in Tomori Bay using Mohid Studio 2016. The model using a finite volume approach with a tidal model driven by the results of Geospatial Information Agency (BIG) predictions placed on the open boundary of the model. The modeling results are compared with the measurement results in Tomori Bay. The tidal current velocity in the high tide conditions increases the current velocity at the bay neck and weakens after passing Tokobae Island. The current velocity on the west side of Tokobae island is higher than that of the east of Tokobae. At the mouth of the bay, the current velocity on the north side is higher than at the south side of the bay mouth. The tidal current velocity is higher than the residual current with a maximum tidal current velocity of 25.3 cms ⁻¹ and a maximum velocity of residual current 12.6 cms ⁻¹ . The residual current that describes the fate of pollutants while in the Tomori Bay waters. The residual flow pattern shows a vortex on the north side of the bay mouth and to the southeast of Tokobae Island.
... The heat content in Tokyo Bay is mainly dominated by advective heat transfer related to residual currents (Hinata et al. 2001). Observations and modeling have demonstrated that the residual currents in Tokyo Bay are characterized by strong cyclonic and weak anti-cyclonic circulation at the bay head and bay center, respectively; these circulations are strongly influenced by wind forcing (Unoki et al. 1980;Guo and Yanagi 1996). When southerly/northerly winds prevail, upwelling occurs along the southwest/east coast, inducing internal Kelvin waves propagating cyclonically along the coast (Suzuki and Matsuyama 2000); consequently, bay head water temperatures increase/decrease (Tabeta and Fujino 1996;Hinata et al. 2001). ...
... The model results demonstrate that the Tokyo Bay summer circulation is characterized by anticlockwise circulation at the bay head area and clockwise circulation behind Futtsu cape in the central bay. The model effectively reproduces observed (Unoki et al. 1980) and modeled (Guo and Yanagi 1996) circulation variations characteristics in Tokyo Bay (the results for spring, fall, and winter are not shown). Figure 3 presents time serials of simulated surface water temperature (red line) and 10-year averaged observations from 2003 to 2013 (black line) at station A (thick lines) and station B (thin lines). ...
The effect of wind on summer water temperature trends in a semi-closed bay (Tokyo Bay, Japan) is examined through several numerical experiments using a high-resolution three-dimensional ocean model. The model is executed under no-wind and uniform southerly/northerly wind conditions, and monthly mean currents and temperature distributions and heat transport in Tokyo Bay for July are calculated. The model results show that wind has a significant effect on heat transport and temperature distribution in the bay. (1) When a southerly wind prevails northward cool water transport intensifies while southward warm water transport declines, thus decreasing the water temperature in the central bay area while increasing temperature at the bay head. (2) A northerly wind has an opposing effect and decreases the water temperature in coastal bay head area while increase the temperature along the southwest coast. The results also suggest that the trend of increasing southerly wind amplitude may have affected water temperature trends in Tokyo Bay from 1979 to 1997. The model results demonstrated that the an intensified southerly wind lowers water temperatures in most areas of the bay by enhancing upwelling and open ocean-water intrusion near the bay mouth while increases temperatures in the bottom layer of the bay head by suppressing southward warm water transport.
... Eelgrass was chosen as a model seagrass because it has various diaspores and is a well-studied aquatic plant worldwide. Kurihama Bay was also chosen as a model site because it is located at the mouth of Tokyo Bay, where the spatial gradients of water temperature and salinity are gradual (Guo & Yanagi 1996), and there are other eelgrass beds near the study site (Shoji & Hasegawa 2004, Tanaka et al. 2011). In addition, we used laboratory experiments to examine the watercolumn dynamics of the diaspores, specifically wheth er they have negative or positive buoyancy. ...
Seed production and dispersal are key processes in plant population dynamics and gene flow. However, few quantitative studies have followed these processes in aquatic plants. We investigated the abundance of seeds produced and dispersed by the seagrass Zostera marina L. at a protected site within an enclosed bay. We also examined the buoyancy potential of seed dispersal units (diaspores) in the laboratory. Field observations showed that 31% of the total potentially produced seeds were dispersed as decayed reproductive shoots on the sea bottom of the parent bed, whereas 14% were dispersed in spathes (a component of reproductive shoots; seeds are contained inside) detached from live reproductive shoots. However, more than half of the dispersed spathes were negatively buoyant because of the weight of the ripe seeds they contained. Thus, <6% of potentially produced seeds were dispersed by rafting away from the parent bed. The abundance of ripe seeds dispersed was comparable to that of seeds in the parent bed sediment. The fate of the remaining 54% of total potentially produced seeds was not detected, and they were assumed to be immature or to have been consumed by herbivores. Fewer than 5% of the dispersed seeds had germinated. Our results show that most seeds were dispersed within the parent bed, supporting one of the fitness-related seed-dispersal hypotheses, namely that dispersal mechanisms play a role in bed maintenance and increased genetic diversity.
... However, it is very difficult to obtain the labor, equipment, and financial resources required to engage dozens of survey ships simultaneously to make synchronous observations. In practice, nonsynchronous data (e.g., data collected at different stations at different times by one ship) or so-called climatological mean data (i.e., the statistical means of data measured on several cruises over many years) are most widely used in diagnostic models, and the impact of intratidal variations of temperature and salinity on density-driven currents has seldom been reported [e.g., Fujio and Imasato, 1991;Yanagi and Takahashi, 1993;Guo and Yanagi, 1996;Guo et al., 2004;Lee et al., 2004;Lee and Chao, 2003;Liu et al., 2010]. ...
... The nonsynchronous data and the tidally averaged data were spatially interpolated to all the grid points and fixed throughout the calculation. Sarmiento and Bryan [1982] proposed the concept of robust diagnostic model, which has since been widely used by many studies to calculate density-related currents [Fujio and Imasato, 1991;Yanagi and Takahashi, 1993;Guo and Yanagi, 1996;Guo et al., 2004;Lee et al., 2004;Lee and Chao, 2003;Wright et al., 2006;Liu et al., 2010]. ...
Using synchronous observational water temperature and salinity data collected simultaneously by 21 ships in summer and a three-dimensional robust diagnostic model, we calculated the density-driven current in Jiaozhou Bay (JZB), a semi-enclosed bay in the Yellow Sea. Special attention was paid to the influences of intra-tidal variations in temperature and salinity on the density-driven current. The density-driven current in JZB has a maximum speed of ~0.1 ms-1 and is stronger than the tide-induced residual current in some places. The density-driven current is characterized by the intrusion of high-density (low-density) water in deep (shallow) areas. The results of the diagnostic model depend heavily on the observational data. For example, the density-driven current calculated from non-synchronous data obtained by one ship at the same 21 stations is not consistent with that calculated from synchronous data because the non-synchronous data correspond to different tidal phases at different stations. The intra-tidal variations of the density field result in a false spatial variation of density in the non-synchronous data, which induces a false density-driven current that is of the same order as that calculated from the synchronous data. In contrast, the tidally averaged water temperature and salinity, which were used to remove intra-tidal variations from the synchronous data, diagnosed a density-driven current consistent with that from synchronous data. We therefore conclude that it is not necessary to explicitly resolve the intra-tidal variations in density in the calculation of density-driven current, but it is necessary to remove intra-tidal variations in the density field before the calculation.
