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1.
In order to understand the actual formation process of the North Pacific Intermediate Water (NPIW), structure of subsurface intrusions of the Oyashio water and the mixing of the Oyashio and the Kuroshio waters in and around the Kuroshio Extension (KE) were examined on the basis of a synoptic CTD observation carried out in May-June 1992. The fresh Oyashio water in the south of Hokkaido was transported into KE region through the Mixed Water Region (MWR) in the form of subsurface intrusions along two main paths. The one was along the east coast of northern Japan through the First Branch of the Oyashio (FBO) and the other along the eastern face of a warm streamer which connected KE with a warm core ring through the Second Branch of the Oyashio (SBO). The fresh Oyashio water extended southward through FBO strongly mixed with the saline NPIW transported by the Kuroshio in the south of Japan (old NPIW) in and around the warm streamer. On the other hand, the one through SBO well preserved its original properties and extended eastward beyond 150°E along KE with a form of rather narrow band. The intrusion ejected Oyashio water lens with a diameter of 50–60 km southward across KE axis and split northward into the MWR involved in the interaction of KE and a warm core ring, which were supposed to be primary processes of new NPIW formation. 相似文献
2.
Since the Intermediate Oyashio Water (IOW) gradually accumulates in Sagami Bay, it can reasonably be supposed that the IOW
also flows out from Sagami Bay, even though it may be altered by mixing with other waters. We have occasionally observed a
water less than 34.2 psu with a potential density of 26.8 at the southeastern area off Izu Peninsula in July 1993 by the training
vessel Seisui-maru of Mie University. Observational data supplied by the Japan Meteorological Agency and the Kanagawa Prefectural
Fisheries Experimental Station show that the IOW of less than 34.1 psu was observed at northern stations of the line PT (KJ)
off the Boso Peninsula and to the east of Oshima in the late spring 1993. Based upon these observations, it is concluded that
the IOW flows out from Sagami Bay into the Shikoku Basin along southeastern area off the Izu Peninsula. The less saline water
(<34.2 psu) was also observed to the west of Miyake-jima during the same cruise, and the westward intrusion of IOW from south
of the Boso Peninsula to the Shikoku Basin through the gate area of the Kuroshio path over the Izu Ridge was detected. This
event indicated that the IOW branched south of the Boso Peninsula and flowed into Sagami Bay and/or into the gate area over
the Izu Ridge. The southward intrusion of IOW into the south of the Boso Peninsula is discussed in relation to the latitudinal
location of the main axes of the Kuroshio and the Oyashio.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
3.
基于1982-2016年的OISST资料分析了西-亚北极锋(The Western Subarctic front,WSAF;37°N-45°N,146°E-152°E)强度与位置的季节及年际变化特征,结果表明:冬季WSAF强度最大,平均位置最靠南;夏季WSAF强度最小,平均位置最靠北;春秋两季WSAF强度、平均位置相当,位于冬夏之间;1982-2016年,WSAF强度逐渐增强,分布位置逐渐缓慢南移;各季节WSAF强度最大值稳定位于149°E附近,WSAF平均位置自西向东不断北移。在此基础上,分析了不同季节WSAF强度与黑潮-亲潮交汇区(The Kuroshio-Oyashio Confluence Region,KOCR)内水体性质的关系:KOCR内黑潮水特征显著时WSAF强度小,黑潮水特征不显著时WSAF强度大;利用EOF分析探寻了WSAF强度年际变化与KOCR内海温的关系:不同季节内WSAF年际变化与KOCR内海温相关性不显著,春、夏、秋季,随着KOCR内海温升高,WSAF强度减弱,而冬季WSAF强度随KOCR内海温升高而增强。 相似文献
4.
Ryuichiro Inoue Jiro Yoshida Yutaka Hiroe Kousei Komatsu Kiyoshi Kawasaki Ichiro Yasuda 《Journal of Oceanography》2003,59(2):211-224
The mixing processes in the Mixed Water Region (MWR) that lead to changes in the properties of North Pacific Intermediate
Water (NPIW) have been studied using observational data sets obtained in May–June 1998. Neutral surfaces, the equation of
water mass conversion rate on neutral surfaces and the equation of vertical velocity across neutral surfaces have been used
to distinguish dominant processes by assuming the horizontal scale to be the streamer scale (under 100 km). The possibility
of double diffusive convection is also discussed in relation to the density ratio. These results may be summarized as follows:
(1) the difference between the potential density surface and the neutral surface may rise to −0.04 kg/m3 around the source water of NPIW; (2) horizontal diffusion causes strong modifications of the source water of NPIW; (3) the
density range within which strong modification of the source water of NPIW occurs becomes dense from the northern part of
MWR near the Oyashio Front to the southern part near the Kuroshio Front, and to the eastern part. Our modeling of these processes
shows that cabbeling has effects on the density increment of the source water of NPIW in the northern and southern part of
MWR. Double diffusive convection has effects on the density increment of the source water of NPIW, mainly in the northern
part of MWR. The possible density increment due to cabbeling in these areas is estimated to be 0.01≈0.03 kg/m3. The possible density increment due to double diffusive convection is 0.01≈0.03 kg/m3. The total density increment due to cabbeling and double diffusive convection amounts to 0.06 kg/m3.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
5.
The annual transport of anthropogenic carbon (Canth) to the North Pacific Intermediate Water (NPIW) from the Western Subarctic Gyre (WSG) has been re-estimated by using newly
estimated Oyashio transport and Canth concentration, the latter calculated by the recently-established “ΔC*” method with some modifications. Estimated annual Canth transport through the nearshore Oyashio west of 146°E was 0.020 ± 0.010 GtC y−1, closely approximating the previous estimation based on a 1-D model calibrated with the CFC vertical distribution. The present
study, however, found that an additional 0.025 ± 0.010 GtC y−1 of Canth was transported into NPIW in the region east of 146°E. Total Canth transport, 0.045 GtC y−1, contributes about 35% of annual Canth accumulation of the whole temperate North Pacific.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
6.
Tomoharu Senjyu Noriko Asano Masaji Matsuyama Takashi Ishimaru 《Journal of Oceanography》1998,54(1):29-44
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} at depths of 320–500 m from the Oshima East Channel to the center of the
bay. On the other hand, the LSW was absent in Sagami Bay in the period of September–November 1994, though it was always found
to the south off the Boso Peninsula. Salinity and dissolved oxygen distributions on relevant isopycnal surfaces and water
characteristics of LSW cores revealed that the LSW intruded from the south off the Boso Peninsula to Sagami Bay through the
Oshima East Channel. The LSW cores were distributed on the continental slope along 500–1000 m isobaths and its onshore-offshore
scales were two to three times the internal deformation radius. Initial phosphate concentrations in the LSW revealed its origin
in the northern seas. These facts suggest that the observed LSW is the submerged Oyashio Water and it flows southwestward
along the continental slope as a density current in the rotating fluid. The variation of the LSW near the center of Sagami
Bay is closely related to the Kuroshio flow path. The duration of LSW in Sagami Bay is 0.5 to 1.5 months. 相似文献
7.
In order to confirm the results of the authors’ previous work, which found that the existence of disturbances smaller than
meso-scale eddies is important in large-scale mixing process between the Oyashio and Kuroshio waters in the intermediate layer,
the results of an eddy-resolving model experiment are analyzed and compared with those of an eddy-permitting model. The intermediate
salinity minimum given in the initial condition weakens as integration advances in the eddy-permitting model, while it recovers
rapidly and is maintained thereafter in the eddy-resolving model, initialized from the unrealistic salinity distribution of
the former. Filament-like fine structures in temperature and salinity develop actively in the latter, which are much smaller
in horizontal width than meso-scale eddies, suggesting the importance of such disturbances in the large-scale mixing. The
mixing ratio of the Oyashio water defined by the original Oyashio and Kuroshio waters shows that its value is generally higher
in the intermediate lower sub-layer than in the intermediate upper sub-layer in the Mixed Water Region, and the salinity minimum
exists between layers with low and high values of the mixing ratio with its strong vertical gradient. The eddy transports
of the Oyashio and Kuroshio waters in an isopycnal layer are divided into four components, usual isopycnal mixing of temperature
and salinity being dominant, followed by the component associated with the thickness flux. The southward eddy transport of
the Oyashio water and the northward eddy transport of the Kuroshio water are not symmetric to each other because the thickness-flux-associated
components are in the same direction (southward). 相似文献
8.
In this study we test Talley's hypothesis that Oyashio winter mixed-layer water (26.5–26.6σ θ) increases its density to produce the North Pacific Intermediate Water (NPIW) salinity minimum (26.7– 26.8σθ) in the Mixed Water Region, assuming a combination of cabbeling and double diffusion. The possible density change of Oyashio
winter mixed-layer water is discussed using an instantaneous ratio of the change of temperature and salinity along any particular
intrusion (R
l
). We estimate the range of R
l
DD
required to convert Oyashio winter mixed-layer water to the NPIW salinity minimum due to double diffusion, and then assume
double-diffusive intrusions as this conversion mechanism. A double-diffusive intrusion model is used to estimate R
l
DD
in a situation where salt fingering dominates vertical mixing, as well as to determine whether Oyashio winter mixed-layer
water can become the NPIW salinity minimum. Possible density changes are estimated from the model R
l
DD
by assuming the amount of density change due to cabbeling. From these results, we conclude that Oyashio winter mixed-layer
water contributes to a freshening of the lighter layer of the NPIW salinity minimum (around 26.70σθ) in the MWR. 相似文献
9.
Eight-year observation results of DIC from 1996 to 2003 in the Oyashio region have been analyzed to obtain a climatological
view of its seasonal variation and interannual variation. Data of DIC obtained by several institutes are synthesized to give
a dataset with an uncertainty lower than 5 μmol/kg. The obtained climatology of NDIC seasonal variation in the Oyashio mixed layer shows a seasonal amplitude of 176 μmol/kg, with a maximum in January and a minimum in September. These features closely resemble those observed in the southern
half of the western subarctic North Pacific (WSNP) including Station KNOT, although the timing of the NDIC maximum is slightly
advanced in the case of the Oyashio. Analysis using a quasi-conservative tracer Cp0 (NDIC - 106NP) shows that among 176 μmol/kg of NDIC seasonal variation, only 16 μmol/kg is attributed to hydrographic processes while the remaining 160 μmol/kg is attributed to biological processes. The Cp0 value in the Oyashio mixed layer also resembles that of the WSNP mixed
layer during the months May to November, suggesting further resemblance of the Oyashio water mass to that of WSNP in terms
of carbon dynamics. The present results also suggest that a single data obtained in Oyashio mixed layer contains 30 μmol/kg of potential uncertainty for the representativity of this region, which leads to a note about a need to treat with
caution results obtained by a single observation in this region. 相似文献
10.
In order to examine the formation, distribution and transport of North Pacific Intermediate Water (NPIW), repeated hydrographic
observations along several lines in the western North Pacific were carried out in the period from 1996 to 2001. NPIW formation
can be described as follows: (1) Oyashio water extends south of the Subarctic Boundary and meets Kuroshio water in intermediate
layers; (2) active mixing between Oyashio and Kuroshio waters occurs in intermediate layers; (3) the mixing of Oyashio and
Kuroshio waters and salinity minimum formation around the potential density of 26.8σθ proceed to the east. It is found that Kuroshio water flows eastward even in the region north of 40°N across the 165°E line,
showing that Kuroshio water extends north of the Subarctic Boundary. Volume transports of Oyashio and Kuroshio components
(relative to 2000 dbar) integrated in the potential density range of 26.6–27.4σθ along the Kuroshio Extension across 152°E–165°E
are estimated to be 7–8 Sv (106 m3s−1) and 9–10 Sv, respectively, which is consistent with recent work.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
11.
A series of numerical experiments were conducted with a high-resolution (eddy-permitting) North Pacific model to simulate the formation and spreading of the salinity minimum associated with the North Pacific Intermediate Water (NPIW). It was found that two factors are required to simulate a realistic configuration of the salinity minimum: a realistic wind stress field and small-scale disturbances. The NCEP reanalyzed wind stress data lead to better results than the Hellerman and Rosenstein wind stress data, due to the closer location of the simulated Oyashio and Kuroshio at the western boundary. Small-scale disturbances formed by relaxing computational diffusivity included in the advection scheme promote the large-scale isopycnal mixing between the Oyashio and Kuroshio waters, simulating a realistic configuration of the salinity minimum. A detailed analysis of the Oyashio water transport was carried out on the final three-year data of the experiment with reduced computational diffusivity. Simulated transport of the Kuroshio Extension in the intermediate layer is generally smaller than the observed value, while those of the Oyashio and the flow at the subarctic front are comparable to the observed levels. In the Oyashio-Kuroshio interfrontal zone the zonally integrated southward transport of the Oyashio water (140-155°E) is borne by the eddy activity, though the time-mean flow reveals the existence of a coastal Oyashio intrusion. In the eastern part (155°E-180°) the zonally integrated transport of the Oyashio water indicates a southward peak at the southern edge of the Kuroshio Extension, which corresponds to the branching of the recirculating flow from the Kuroshio Extension. 相似文献
12.
The influence of the Kuroshio flow on the horizontal distribution of North Pacific Intermediate Water (NPIW) in the Shikoku
Basin is examined based upon observational data collected by the training vessel “Seisui-maru” of Mie University together
with oceanographic data compiled by the Japan Oceanographic Data Center (JODC). Although it has been stated that the NPIW
with salinity less than 34.2 psu had been confined to the south of the Kuroshio main axis along the PT (KJ) Line on the eastern
side of the Izu Ridge, a similar tendency can be detected on the western side of the Izu Ridge. Namely, the NPIW on the southern
side of the Kuroshio main axis in the Shihoku Basin does not indicate a tendency to go northward across the Kuroshio main
axis without an increase in salinity of more than 34.2 psu. However, the JODC data show that less saline water (<34.2 psu)
was present on the northern side of the Kuroshio main axis south of the Kii Peninsula in May 1992. Satellite observed sea
surface temperature (SST) data suggested that the Kuroshio approaches the Kii Peninsula after forming a small meander off
Kyushu and some intrusions of the NPIW into the northern coastal side of the Kuroshio main axis occurred in this period. It
is concluded that intrusion of the NPIW with salinity less than 34.2 psu to the northern coastal side through the Kuroshio
main axis occurred during the decay period of the small meander path in May 1992. Based on these observational results, the
source of the salinity minimum water on the northern coastal side of the Kuroshio main axis is discussed.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
13.
Vertical distribution of anthropogenic carbon content of the water (exDIC) in the Oyashio area just outside of the Kuroshio/Oyashio Interfrontal Zone (K/O Zone) was estimated by the simple 1-D advection-diffusion model calibrated by the distribution of chlorofluorocarbons (CFCs). The average concentration of exDIC for = 26.60–27.00 is multiplied by the volume transport of Oyashio water into the North Pacific Intermediate Water (NPIW) to estimate the annual transport of exDIC into NPIW through K/O Zone. The estimated transport of exDIC was 0.018–0.020 GtC/y, which corresponds to 15% of the whole total exDIC accumulation in the temperate North Pacific. A simple assessment using the NPIW 1-box model indicates that the current study explains at least 70% of the total annual transport of exDIC into NPIW, and that small exDIC sources for NPIW still exists in addition to K/O Zone. 相似文献
14.
The salinity minimum frequently occurring in the Mixed Water Region between the Oyashio and Kuroshio Fronts seems to originate from the salinity minimum at the density of 26.8σθ called the North Pacific Intermediate Water. We examined water exchange of this region with the Oyashio and the Kuroshio Extension using mixing ratio RK defined as (θ - θOY)/(θK - θOY) × 100, where θOY, θK, and θ represent potential temperature of the Oyashio and Kuroshio Waters and their mixture on the isopycnal surfaces, respectively. CTD data were obtained by repeated observation from January 1990 to May 1991. RK increases southward from the Oyashio Front to the Kuroshio Front with the range of −20 to 120%. The gradient of RK on the isopycnal surfaces is large around the Oyashio Front above the 26.8σθ surface, while it is large around the Kuroshio Front below it. This agrees with the average RK in the Mixed Water Region decreasing greatly with the increase of density at densities less dense than 26.8σθ. We calculated thickness and volume transport of the Oyashio between the isopycnal surfaces near the coast of Hokkaido. They increase largely with density at densities less dense than 26.8σθ. It is supposed that the salinity minimum in the Mixed Water Region is the upper limit of the water largely influenced by the Oyashio Water. Its density could depend only on the density structure of the Oyashio. 相似文献
15.
Grazing impact of the copepod community in the Oyashio region of the western subarctic Pacific Ocean
Kazutaka Takahashi Akira Kuwata Hiroaki Saito Keiichiro Ide 《Progress in Oceanography》2008,78(3):222-240
The role of copepod grazing on the ecosystem dynamics in the Oyashio region, western subarctic Pacific was investigated during six cruises from June 2001 to June 2002. In situ grazing rates of the copepod community (CGR) were measured by the gut fluorescence method in respect to developmental stages of dominant species. In terms of biomass, more than 80% of the copepod community was dominated by six large calanoid species (Neocalanus cristatus, Neocalanus flemingeri, Neocalanus plumchrus, Eucalanus bungii, Metridia pacifica and Metridia okhotensis) throughout the year. Resulting from the observed pattern of the interzonal migrating copepods, the CGR in the Oyashio region was divided into three phases, i.e. spring (bloom), summer (post-bloom) and autumn-winter phase. During the spring bloom, late copepodites of the interzonal migrating species, N. cristatus, N. flemingeri and E. bungii appeared in the surface layer (0-50 m) to consume the production of the bloom, resulting in a high grazing rate of the copepod community (7.9 mg Chl m−2 d−1), though its impact on phytoplankton community was low due to the high primary productivity. During the post-bloom period, although the copepod community which was dominated by N. cristatus, N. plumchrus, M. pacifica and newly recruited E. bungii still maintained a high biomass, the CGR was generally lower (1.8-2.6 mg Chl m−2 d−1 for June and August 2001), probably due to the lower availability of phytoplankton. Nevertheless, the highest CGR was also observed during this period (10.5 mg Chl m−2 d−1 in June 2002). The high CGR on autotrophic carbon accounted for 69% of the primary production, suggesting that the copepod community in the Oyashio region potentially terminates the phytoplankton bloom. Abundant occurrence of young E. bungii, which is a characteristic phenomenon in the Oyashio region, was largely responsible for the high grazing pressure in June 2002 suggesting that success of reproduction, growth, and survival in E. bungii during the spring bloom is an important factor in controlling phytoplankton abundance during the post-bloom season. During autumn and winter, CGR was the lowest in the year (0.29-0.38 mg Chl. m−2 d−1) due to the disappearance of the interzonal migrating copepods from the surface layer. Diel migrant M. pacifica was the most important grazer during this period. The annual ingestion of the copepod community is estimated as 37.7 gC m−2 on autotrophic carbon (converted using C:Chl ratio of 30) or 137.9 gC m−2 on suspended particles (using C:Chl ratio of in situ value, 58-191), accounting for 13% and 46% of annual primary production, respectively. This study confirms that copepod grazing is an important pathway in carbon flow in the Oyashio region and in particular their role in the phytoplankton dynamics is significant for the termination of the spring bloom. 相似文献
16.
Simulation of Formation and Spreading of Salinity Minimum Associated with NPIW Using a High-Resolution Model 总被引:1,自引:2,他引:1
A series of numerical experiments were conducted with a high-resolution (eddy-permitting) North Pacific model to simulate
the formation and spreading of the salinity minimum associated with the North Pacific Intermediate Water (NPIW). It was found
that two factors are required to simulate a realistic configuration of the salinity minimum: a realistic wind stress field
and small-scale disturbances. The NCEP reanalyzed wind stress data lead to better results than the Hellerman and Rosenstein
wind stress data, due to the closer location of the simulated Oyashio and Kuroshio at the western boundary. Small-scale disturbances
formed by relaxing computational diffusivity included in the advection scheme promote the large-scale isopycnal mixing between
the Oyashio and Kuroshio waters, simulating a realistic configuration of the salinity minimum. A detailed analysis of the
Oyashio water transport was carried out on the final three-year data of the experiment with reduced computational diffusivity.
Simulated transport of the Kuroshio Extension in the intermediate layer is generally smaller than the observed value, while
those of the Oyashio and the flow at the subarctic front are comparable to the observed levels. In the Oyashio-Kuroshio interfrontal
zone the zonally integrated southward transport of the Oyashio water (140–155°E) is borne by the eddy activity, though the
time-mean flow reveals the existence of a coastal Oyashio intrusion. In the eastern part (155°E–180°) the zonally integrated
transport of the Oyashio water indicates a southward peak at the southern edge of the Kuroshio Extension, which corresponds
to the branching of the recirculating flow from the Kuroshio Extension.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
17.
Masashi Kusakabe Andrey Andreev Vyacheslav Lobanov Igor Zhabin Yuichiro Kumamoto Akihiro Murata 《Journal of Oceanography》2002,58(5):691-701
Data from the R/V Mirai cruise (May–June 2000) have been examined to discover how mesoscale processes associated with eddy dynamics direct affect
the water masses, the distributions and the vertical fluxes of the dissolved oxygen, nutrients and dissolved inorganic carbon
in the western subarctic Pacific. Using maps of the temperature, salinity, dissolved oxygen, nutrients, chlorophyll and sea-air
pCO2 difference we show that the boundaries of the anticyclone eddies in the study region were composed of high productivity coastal
Oyashio water. The coastal waters were wrapped around the anticyclone eddies (thus creating a high productivity belt) and
intruded inside of them. Using SeaWifs data we demonstrate that temporal variations in the position and the strength of anticyclone
eddies advected the Kuril island coastal high productivity waters to the pelagic part, resulting in temporal variations of
the chlorophyll in the Oyashio region. Computed vertical fluxes of the dissolved oxygen (DO), inorganic carbon (DIC) and silicate
show that the anticylonic eddies in the Kuroshio-Oyashio Zone are characterized by enhanced vertical fluxes of the DO and
DIC between the upper (σθ = 26.7–27.0) and lower (σθ = 27.1–27.5) intermediate layer, probably due to the intrusions of the Oyashio waters into the eddies.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
18.
In a previous paper (Oguma and Nagata, 2002), it was shown that frequency distributions of temperature and salinity in the
sea off Sanriku Coast, Japan are skewed, and sometimes observed values exceed m + 5σ (m = mean, σ = standard deviation). This means that, if we apply a 3σ criterion for a range check, many real data would be lost.
We have expanded our analysis to the subarctic North Pacific, the subarctic North Atlantic and their surrounding areas, by
computing the distributions of skewness and kurtosis. It is found that the region of high positive skewness extends in an
east-north-east direction in the Mixed Water Region from off Sanriku, and reaches to about 155°E. A high negative skewness
zone is recognized along the southern margin of the Kuroshio Extension. These are thought to be generated by the breaking
of the meander of the Kuroshio Extension and subsequent ejection of warm and cold eddies to the north and south, respectively.
Other high positive skewness areas are found to the south of Kuril Islands and in the Japan Sea. These are generated due to
very sharp vertical gradients of temperature and salinity. The situation in the North Atlantic is very similar to the North
Pacific, though the detailed nature is changed due to differences of oceanographic condition. The effect of grid size on the
skewed nature of the distribution is also discussed.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
19.
Osamu Shida Tomonori Hamatsu Akira Nishimura Akifumi Suzaki Jun Yamamoto Kazushi Miyashita Yasunori Sakurai 《Deep Sea Research Part II: Topical Studies in Oceanography》2007,54(23-26):2822
The Japanese Pacific walleye pollock (Theragra chalcogramma) stock is the largest stock of this species in Japanese waters. It is a key component of the Oyashio ecosystem. In southern Hokkaido waters, these fish spawn mainly during January and February near the mouth of Funka Bay (FB), and most eggs and larvae are transported into FB. During midsummer juvenile pollock migrate along the southern coast of Hokkaido to a nursery ground on the continental shelf off eastern Hokkaido (Doto area). However, some eggs and larvae are transported southward to the Tohoku region (TR). Transport depends largely on the Oyashio, which generally flows southward along the eastern coasts of Hokkaido and Tohoku. Thus, this stock has two different recruitment routes: FB–Doto and FB–TR. In the 1980s, when the southward flow of the Oyashio was strong, the number of age-2 pollock estimated from a virtual population analysis (VPA) indicated that recruitment to the entire stock remained at a medium level. In the 1990s, when the Oyashio weakened, strong year-classes occurred in 1991, 1994, and 1995, but not in the latter half of the 1990s. Juvenile catches in the TR by commercial fisheries, which can be taken as indices of recruitment level via FB–TR, were high during the 1980s and decreased in the 1990s. Although there was no significant difference in the average number of recruits between the 1980s and the 1990s as estimated from a VPA, the recruitment patterns differed between the two decades. Here, we propose that recruitment routes of this stock shifted in response to environmental changes. 相似文献
20.
The temperature and salinity data obtained by the Iwate Fisheries Technology Center for the 25-year period from 1971 to 1995
were analyzed to clarify the seasonal variations in the sea off Sanriku, Japan. The variations of three typical waters found
in this region, the Tsugaru Current water, the Oyashio water, and the Kuroshio water are discussed in terms, of a T-S scatter
diagram referring to the water mass classification proposed by Hanawa and Mitsudera (1986). The mean temperature and salinity
fields averaged for each month show clear seasonal variation. Distributions of the Tsugaru Current water and the Oyashio water
can barely be distinguished in the fields deeper than 200 m since the Tsugaru Current has a shallow structure; however, the
fields at 100 m depth indicate remarkable seasonal variation in the area of the Tsugaru Current. At 100 m depth, the temperature
and salinity fronts between the Tsugaru Current water and the Oyashio water gradually disappear in January through April,
appear again in May, then become clearest in September.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献