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Vertical profiles of potential temperature (θ), salinity (S), dissolved oxygen (O) and potential density (σ θ ) at Stn. 7. Low temperature, low salinity and high dissolved oxygen water is seen at depths of 380-500 m.
Source publication
Intermediate intrusion of low salinity water (LSW) into Sagami Bay was investigated on the basis of CTD data taken in Sagami
Bay and off the Boso Peninsula in 1993–1994. In October 1993, water of low temperature (<7.0°C), low salinity (<34.20 psu)
and high dissolved oxygen concentration (>3.5 ml I−1) intruded along the isopycnal surface of {ie29-1}...
Contexts in source publication
Context 1
... June [15][16]1994 Seiyo Maru 19 July [25][26]1994 Seiyo Maru 19 August [24][25][26]1994 Seiyo Maru 13 August 29- September 1, 1994 Seiyo Maru 11 September [18][19]1994 Seiyo Maru 30 October [13][14][15][16][17][18]1994 Shin'yo Maru 41 November [10][11]1994 Seiyo Maru 21 (S), dissolved oxygen (O) and potential density (σ θ ) at Stn. 7 are shown in Fig. 3 as a typical profile of the LSW. The water of low temperature, low salinity and high dissolved oxygen concentration is discernible between depths of 380 and 500 m. Since the temperature and salinity distributions compensate each other to the density, the intruding structure cannot be found in the σ θ profile. The salinity and dissolved ...
Context 2
... was observed during October 14-18, 1993. The location of CTD stations in the survey and the bottom topography of Sagami Bay are shown in Fig. 2 that of low salinity (less than 34.15 psu). This two-core system (low temperature core and high oxygen core) shows a splitting intrusion of the LSW, as seen in the salinity and dissolved oxygen profiles (Fig. 3). A similar distribution of water characteristics is found in Line C (not ...
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Citations
... However, there could be an opposite situation that temperature and salinity increase and decrease in the middepth of profiles, that is, temperature or salinity inversions (Chrysagi et al., 2022;Kim et al., 2020;Roden, 1964). These inversions are widely observed near fronts, fjords, and basins (Alford et al., 2005;Chrysagi et al., 2022;Hopkins et al., 2012;Lentz, 2003;Senjyu et al., 1998). The water inversions have an indicative and validating effect on hydrological circulation and water masses. ...
... The water inversions have an indicative and validating effect on hydrological circulation and water masses. It also correlates with the distribution of biochemical elements such as dissolved oxygen and chlorophyll-a in the water, and can have a significant effect on the distribution of fish resources (Holtermann et al., 2017(Holtermann et al., , 2020Pang et al., 2017;Senjyu et al., 1998;Takeoka et al., 1993;Yamamoto et al., 2000;Zhou et al., 2008). The understanding of water inversions must facilitate the The presence of water inversions can play an important role in modulating local ecological activities. ...
In the southern Yellow Sea (SYS) there are temperature and salinity inversions associated with the presence of middepth low temperature and salinity water. Many questions regarding with the inversions, such as the seasonal variation and transformation mechanism, still remain unexplained. In this study, based on hydrographic measurements obtain from 12 cruises within 6‐year (2017–2022), we explored the distribution, seasonality, generation, and transformation mechanism of temperature and salinity inversions in the SYS. Observations reveal widespread temperature and salinity inversions in the Yellow Sea (YS) during both spring and summer. More temperature and salinity inversions are found in spring and summer, respectively. The relative motion between the fresh, cold, high‐dissolved‐oxygen (DO) water at the local shelf/slope and the salty, warm, low‐DO water at the central trough is the key to answering the formation of temperature/salinity inversions. The salinity at the low‐salinity water (LSW) layer increases towards the central YS suggesting the origin of LSW at the local shelf/slope region. Assuming the gain of salinity is caused primarily by vertical diffusion at the upper and lower boundary of the LSW, the propagation speed of the LSW lense is estimated which compares favorably with the magnitude of observed residual currents at the LSW layer. We further note that the depth of subsurface dissolved oxygen maximum agrees well with the LSW layer depth, especially for summer. The influence of the lateral transport of nutrients, and dissolved oxygen on the local biogeochemical environment in the YS is worth further examination.
... However, transitional species, pseudoceanic species and wide-ranging species were distributed in both the outer bay and bay mouth areas (Fig. 9). For the transitional species of L. ochotensis, eggs or larvae are likely advected by the IOW, which is a cold current flowing from the northeast of Japan that is consistently present in the mesopelagic layer in Sagami Bay and the mouth of Tokyo Bay (Senjyu et al. 1989;Yanagi et al. 1999;Sekine and Uchiyama 2002). Larvae of that species are distributed in the 300-700 m layer in Sagami Bay, which is consistent with the depth of IOW (Miya 1995). ...
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.
... The first survey around the islands (K6 and K7) also showed higher densities in the immediate and eastern regions, especially in the lower epipelagic layer ( Figure 3b). As it is known that one of the branches of Oyashio, the western boundary current of the western subarctic gyre, reaches Sagami Bay or flows westward from the Izu Islands (Marumo, 1966;Sekine & Uchiyama, 2002;Senjyu, Asano, Matsuyama, & Ishimaru, 1998;Taira & Teramoto, 1985;Yang, Nagata, Taira, & Kawabe, 1993a, 1993b, the higher densities are attributed to the influence of Oyashio water. In the Kuroshio Extension area, the highest water density (lowest temperature and salinity) was shown north of the axis (Oyashio side) on the eastern side of F I G U R E 4 Horizontal distribution maps of planktonic stage of Japanese sardine (Sardinops melanostictus), planktonic stage of mackerels including chub mackerel (Scomber japonicus) and spotted mackerel (Scomber australasicus), and planktonic copepods (adult and juvenile). ...
The sustainable use of marine resources requires understanding the surrounding ecosystem and elucidating mechanisms of variation. However, we still lack a comprehensive understanding of environmental variation in the spawning and nursery grounds of important fisheries species Japanese sardine (Sardinops melanostictus) and mackerels (Scomber japonicus and Scomber australasicus) in the northwest Pacific. Here, we investigate detailed physical, chemical, and biological environment variations in the spawning and nursery grounds along the Kuroshio and Kuroshio Extension area from intensive investigation in spawning season (April) of 2013. We found similar water mass property and copepod community in the egg‐rich Kuroshio area and the larvae‐rich downstream Kuroshio Extension area, indicating environmental variability is small during transportation and development processes. The egg‐rich northern Izu Islands region showed high copepod abundance, although low nutrient and chlorophyll concentrations were observed. Eggs were scarce or absent in the second survey 10 days after abundant eggs were observed in the region, along with differences in water property and copepod community. This indicates that not only the location but also the specific water characteristic and copepod community are a determining factor for spawning. Indicator communities of copepod found in our study (indicator community of transportation process from spawning ground, of non‐spawning ground, and of reproductive area in the Kuroshio Extension area) would be a key factor for recruitment prediction.
... By contrast, in the eastern side of the study area, the K of G. leonina was significantly higher than that of G. punctata at the tip of the Miura Peninsula (S3) or almost equal to that of G. punctata on the Pacific side of the Boso Peninsula (B1) (Fig. 6; Table 6). It is well known that nutrient-rich water from the Oyashio Current intrudes into Sagami Bay along the coast of the Boso Peninsula (Senjyu et al. 1998). The ocean dynamics differ between the eastern and western zones of Sagami Bay. ...
The early life history of girellid fishes in Japanese waters is unclear, and little is known about their species-specific reproductive strategies. We examined seasonal changes of distribution patterns for settlement-stage juveniles of Girella punctata and Girella leonina on the rocky shore in the regions of Kanto and Izu, Japan, to infer the influence of the Kuroshio Current on their reproduction. We collected 813 settlement-stage juveniles mainly in Sagami Bay and genetically identified the species. The juveniles of G. punctata were collected on the rocky shore in Sagami Bay during April to August, with the abundant catch in May and June. Thus, we infer that juvenile G. punctata ubiquitously inhabit the rocky shore in the area in spring and summer. By contrast, juveniles of G. leonina were rarely collected in Sagami Bay, with a total catch of only 66. Notably, no juveniles were collected during the wintertime in Sagami Bay, although an abundant catch of G. leonina had been previously reported for Sagami Nada off Sagami Bay during January to March. This clear-cut difference between the areas likely reflects the difference in proximity to the path of the Kuroshio Current. We expect that the Kuroshio Current strongly influences the reproductive success of G. leonina.
... The Oyashio, the western boundary current of the western subarctic gyre, flows southward and partially sinks under the Kuroshio Water along the east coast of Japan. One of its branches, the Intermediate Oyashio Water (IOW) characterized by its salinity minimum layer (SML), passes between the Boso Peninsula and the Kuroshio axis at a depth of 400-500 m in the opposite direction of the Kuroshio and then either flows into Sagami Bay or passes through a deeper layer between two of the Izu Islands, Miyake and Hachijo (Marumo 1966;Taira and Teramoto 1985;Yang et al. 1993a, b;Senjyu et al. 1998;Sekine and Uchiyama 2002). ...
A continuous survey examined short-term variations in the zooplankton community and physical ocean environment from the northeastern Izu Islands to Boso Peninsula in Japan. High copepod abundance and small upwellings in the surface layer and salinity minimum layer in the subsurface were observed on the north side of coastal fronts in the westernmost transect, moving southward as the Kuroshio Current left the Boso Peninsula. Thus, the salinity minimum layer might be a key factor forming upwelling and the fronts, leading to large abundance of coastal copepods off the northeastern Izu Islands. A community structure analysis of calanoid copepods revealed an intermediate belt assemblage between coastal and offshore (Kuroshio) assemblages. Copepod abundance was remarkably low and Ctenocalanus vanus dominated (nearly 37%) in the intermediate belt zone, indicating that C. vanus has a relatively high tolerance to adverse environments for calanoid copepods. As the Kuroshio Current left the Boso Peninsula, the coastal assemblage expanded in the same direction, and the intermediate belt assemblage off the northeastern Izu Islands disappeared. The largest population of Calanus sinicus was found along the two western transects off the northeastern Izu Islands (>1000 m depth), which was assumed to be transported from Sagami Bay and advanced southwestward while growing from copepodite stages CIII to CV. Larvae of C. sinicus would be an important food for fish larvae in addition to Paracalanus parvus s.l., the numerically dominant species in the coastal assemblage, and C. vanus under the adverse conditions for coastal copepods.
... However, it is also one of the most complex bays, hydrographically speaking. Indeed, as well as seasonal stratification events, waters in the Bay can be periodically influenced, at the surface, by runoff water from the surrounding land and from Tokyo Bay, by branches of the Kuroshio Current and, in the mesopelagic zone, by mixtures of Low Salinity Water, and, at times, by intrusions of Oyashio Intermediate Water (Senjyu et al. 1998;Yang et al. 1993b), as well as by periodic passages of typhoons in the summer and autumn months. ...
... The lowest salinity value (34.32) was recorded at night between 497 and 502 m on 15 March. The Low Salinity Water (LSW), found between the 26.5 and 27.1 isopycnals (Senjyu et al. 1998), was located between 235.5 and 635.4 m during the day and between 281.9 and 614.1 m at night. These depth differences were most likely due to the fact that the net samplings were not performed consecutively but over a period of up to 9 days (Night on 15 March, Day on 24 March), rather than to any diel pattern. ...
... These depth differences were most likely due to the fact that the net samplings were not performed consecutively but over a period of up to 9 days (Night on 15 March, Day on 24 March), rather than to any diel pattern. The LSW has been associated with Oyashio Intermediate Water (Senjyu et al. 1998;Yang et al. 1993a), but in the b Estimated from other Desmophyes species; bracts unknown present dataset, the salinity was consistently higher than the 34.2 indicative of that water mass (Sekine and Uchiyama 2002;Senjyu et al. 1998), therefore possibly representing a mixture of waters of northern origin. ...
Siphonophores were sampled using stratified 1.67-m2-mouth 330-μm mesh nets during both day- and nighttime in Sagami Bay (35°0.50′N, 139°20′E), off south-eastern Japan during a 9-day period in March 2006, when the Kuroshio Current was in an offshore non-large meander phase. The samples were collected at 50-m intervals spanning from 1,000 m depth to the surface. Fifty-eight species and 11 eudoxid forms of unknown parentage were collected, of which 5 represent first-time records from Japanese waters, and Clausophyes laetmata Pugh and Pagès 1993, Eudoxia cf. galathea Moser 1925 and Lensia panikkari Daniel 1970 were recorded for the first time not only from Japan but from the entire Pacific Ocean. The highest abundance and diversity was found below the thermocline during the day, and above it at night. A second peak in abundance, around 400 m depth, associated with a decrease in diversity, could be linked to the increase in abundance of a single species—Dimophyes arctica (Chun 1897). The siphonophore communities could be related to the different water masses in the Bay, with an important influence of lateral transport of both tropical and subarctic species into the Bay by the different water masses.
... e sampling location, in the midwater zone east of Oshima Island, was chosen as, due to the dynamism of the ow path of the Kuroshio current, this zone is in uenced by many di erent water masses, with Kuroshio, Oyashio, Sagami Bay, and Tokyo Bay signatures (Grossmann & Lindsay 2013, Senjyu et al. 1998, Shimode et al. 2006). e copepod population on which the present study was performed was therefore assumed to be general enough in taxonomic breadth that the regressions obtained may be applicable to all waters o southern, and along the eastern coast of Japan. ...
Computer-automated image capture and analysis techniques are increasingly used for the study of plankton. Unfortunately, because most of the automatic image processing packages recognize only numbers of pixels and grey scale values, although a great many parameters are automatically measured on each image (area, perimeter, average level of grey, etc. . . .), these do not directly equate to variables that appear in the biological literature. The relationships between prosome lengths and computer-generated characters were derived from images acquired using the ZooScan system for two of the most common copepod families off south–eastern Japan: Calanoida and Poecilostomatoida. The equivalent spherical diameter (ESD), a character automatically measured by the ZooScan-ZooProcess system, was found to be highly correlated with prosome length in the two orders, and a single equation could be established (regression coeecient r2 = 0.943) for all Calanoida excepting those of the family Eucalanidae: PL (mm)0.080.023*ESD (pixels).
... Smallscale geographic differences may also explain the higher genetic distance (0.12) found between the two Japanese L. achilles samples. Indeed, although both were sampled in Sagami Bay, KC782554 was collected between 400 and 600 m, a depth at which waters of northern origin such as the Oyashio Intermediate Water (Senjyu et al., 1998) periodically intrude into the Bay, while KC782553 was collected between 750 and 800 m, a more hydrographically stable layer. The depth of the inter-geographic divergences observed in L. achilles, L. havock and L. multicristata, with K2P genetic distances between 0.16 and 0.25, and between 8.0% and 12.2% nucleotide differences, were similar to the inter-specific variations found between the multistriate Lensia, and those between L. campanella and L. cossack, and may reflect the existence of cryptic species rather than intra-specific variations. ...
The greatest challenge in the study of the cnidarian order Siphonophora lies in the identification of all parts of the fragile
colonies usually separated during net sampling. Species are usually established based on the morphology of at least one
swimming bell of the polygastric stage, and a single genus, Eudoxia, has housed the description of free sexual eudoxid
stages until these can be reliably linked to a polygastric stage. This genus, extensively used until the early 20th century, has
progressively been emptied and, at the present day, contains only one form for which the identification of the polygastric
stage has remained completely enigmatic: Eudoxia macra Totton, 1954. DNA barcoding techniques using the mitochondrial
16S gene allowed this eudoxid stage to finally be linked with its polygastric stage, Lensia cossack Totton, 1941.
... The North Pacific Intermediate Water (NPIW), which originates from the subarctic region, enters the bay within the meso-and bathypelagic zones. The salinity of the mesopelagic water fluctuates according to the strength of the intrusions (Senjyu et al. 1998, Yasuda 2003. These characteristics, along with its easy access for repeated sampling, make Sagami Bay an ideal site for examining the seasonal variation of zooplankton and its relationships with oceanographic conditions throughout the water column, including meso-and bathypelagic zones. ...
... A star indicates the weighted mean temperature (WMT) and salinity (WMS) for each species. Temperature and salinity indicating Kuroshio water, coastal water, and North Pacific Intermediate Water (NPIW) are shown by the grey symbols; the values are referenced from Iwata (1979) and Senjyu et al. (1998Senjyu et al. ( ). et al. 2000, the Sulu and Celebes seas (Johnson et al. 2006), and the waters south of the Kuroshio (Ozawa et al. 2007). This pattern contrasts with that observed in many other pelagic animals, such as copepods and ostracods (Roe 1972, Angel 1993, Yamaguchi et al. 2002, Shimode et al. 2006, Kuriyama & Nishida 2006, in which species diversity peaks in the mesopelagic layer. ...
... In the present study, these species were distributed below 400 m and occurred in May, September, and November 2005 and January 2006 when low-salinity water (<34.2) was present at 400-800 m. According to Senjyu (1998) salinities of less than 34.2 indicate a strong intrusion of subarctic water in the mesopelagic layer of Sagami Bay, suggesting that the abundance of the two boreal species is strongly influenced by subarctic water. ...
The vertical distribution and seasonal variation of pelagic chaetognaths was investigated in Sagami Bay, based on stratified zooplankton samples from the upper 1,400 m. The chaetognaths were most abundant in the 100– 150 m layer in January and May 2005, whereas they were concentrated in the upper 50 m in the other months. Among the 28 species identified, Zonosagitta nagae had the highest mean standing stock, followed by Flaccisagitta enflata and Eukrohnia hamata. Cluster analysis based on species composition and density separated chaetognath communi-ties into four groups (Groups A–D). While the distribution of Group C was unclear due to their rare occurrence, the other groups were more closely associated with depth than with season. The epipelagic group (Group A) was further divided into four sub-groups, which were related to seasonal hydrographic variation. The mesopelagic group (Group B) was mainly composed of samples from the 150–400 m layer, although Group A, in which the epipelagic species Z. nagae dominated, was distributed in this layer from May to July. Below 400 m, all samples were included in the bathypelagic group (Group D). In this group, Eukrohnia hamata was dominant with larger standing stocks than in other tropical-temperate waters, suggesting that intrusions of subarctic water drive the large standing stock of this species. Combined, these observations suggest that the seasonal and vertical patterns of the chaetognath community in Sagami Bay are influenced by hydrographic changes in the epipelagic layer and the submerged subarctic water in the mesopelagic layer.
... Support for a southern origin is indicated by the shelf fauna of southern Japan, which has been referred to as a tropical or subtropical assemblage (Briggs, 1974). The observed species diversity in Sagami Bay could then be the result of several dispersal routes that are accommodated by southern deepwater currents and the northern Oyashio Water flowing southeastward through the Oshima East Channel along the Bosa Peninsula (Tomoharu et al., 1998). If this could be demonstrated, a general accumulation of hyperbenthic deepsea organisms, including Pseudomma, would be expected, and Sagami Bay would be a diversity ''sink-hole'' rather than a speciation center. ...
We used DNA sequences from 18S rDNA (808 bp) and COI mtDNA (599 bp) to infer evolutionary history of northern groups of the deep-sea mysid genus Pseudomma. The V4–V7 regions of 18S show an average of 1.31% sequence divergence between species. A secondary structure model is constructed and used in phylogenetic analyses to allow for different evolutionary rates in paired and unpaired nucleotide partitions. COI is observed as highly variable with uncorrected p-distance averaging 33%. Phylogenies for these sequences were estimated by maximum-likelihood, Bayesian, and maximum-parsimony analyses. More or less similar tree topologies were obtained for each gene with these methods. Pseudomma longisquamosum was placed in a basal clade, using Parapseudomma and Amblyops as outgroups, but the exact relationship of other basal taxa is less clear when results from the two genes are compared. An ancient presence of Pseudomma in the Tethys Sea is suggested by phylogenetic structure, molecular clock considerations, and present distributions. A well-supported Atlantic clade may have diverged from Indo-Pacific groups in the Miocene because of the closure of the Gibraltar Strait. More recent speciation events are proposed in the Norwegian Sea, and an Arctic intrusion from the North Pacific across the Bering Strait is suggested for the circumpolar species Pseudomma truncatum.
