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Goh Onitsuka Akihiko Morimoto Tetsutaro Takikawa Atsushi Watanabe Masatoshi Moku Yutaka Yoshikawa Tetsuo Yanagi 《Estuarine, Coastal and Shelf Science》2009,81(3):401-408
The relationship between island-induced cyclonic eddies and chlorophyll a (chl-a) was investigated using field data and satellite images in the eastern channel of the Tsushima Straits. The maximum chl-a concentration around the leeward eddy of the Tsushima Islands was two or three times greater than that of outside the eddy. Two different mechanisms of chl-a enhancement associated with island-induced cyclonic eddies were found in the post-bloom periods. In summer, when nutrients were depleted in the surface layer, eddy pumping increased the nutrient supply in the euphotic zone, resulting in enhanced chl-a around the shallow thermocline near the eddy core. In late autumn, when the mixed layer deepened over the euphotic zone, the mixed layer depth became shallow due to the doming effect of the cyclonic eddy, therefore, the improved irradiance condition led to an increase in the chl-a concentration in the surface mixed layer. Nighttime satellite visible images showed a number of fishing vessels in the lee region of the Tsushima Islands, implying that the enhanced phytoplankton biomass may have resulted in good feeding conditions for fishes and squids in the Tsushima Straits. 相似文献
3.
Seasonal variation of horizontal material transport through the eastern channel of the Tsushima Straits 总被引：2，自引：2，他引：0
Akihiko Morimoto Tetsutaro Takikawa Goh Onitsuka Atsushi Watanabe Masatoshi Moku Tetsuo Yanagi 《Journal of Oceanography》2009,65(1):61-71
We conducted hydrographic observations ten times in the Tsushima Strait to reveal seasonal variations of horizontal material
transports such as of heat, freshwater, chlorophyll a, and dissolved inorganic nitrogen (DIN) and phosphorus (DIP) through the eastern channel of the Tsushima Strait (ECTS). The
volume, freshwater, and heat transport results are of nearly the same order as results reported in previous studies. The annual
mean DIN and DIP transports of 3.59 kmol/s and 0.29 kmol/s are large relative to those of the Changjiang and the Taiwan Strait
and are horizontally transported through the ECTS. Nutrient transports are high in July–August and October and low in April
and November. Increased nutrient transports in July–August and October are due to the appearance of a cold saline water mass
in the bottom layer of the ECTS. Changes in DIN transports in summer and autumn, which account for two-thirds of the total
annual DIN transport, would have a large effect on the nitrogen budget and biological productivity in the Tsushima Warm Current
region. 相似文献
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Hideyuki Kawamura Toshimichi Ito Naoki Hirose Tetsutaro Takikawa Jong-Hwan Yoon 《Journal of Oceanography》2009,65(4):439-454
The branches of the Tsushima Warm Current (TWC) are realistically reproduced using a three-dimensional ocean general circulation
model (OGCM). Simulated structures of the First Branch and the Second Branch of the TWC (FBTWC and SBTWC) in the eastern Japan
Sea are mainly addressed in this study, being compared with measurement in the period September–October 2000. This is the
first numerical experiment so far in which the OGCM is laterally exerted by real volume transports measured by acoustic Doppler
current profiler (ADCP) through the Tsushima Straits and the Tsugaru Strait. In addition, sea level variation measured by
tide-stations along the Japanese coast as well as satellite altimeters is assimilated into the OGCM through a sequential data
assimilation method. It is demonstrated that the assimilation of sea level variation at the coastal tide-stations is useful
in reproducing oceanic conditions in the nearshore region. We also examine the seasonal variation of the branches of the TWC
in the eastern Japan Sea in 2000. It is suggested as a consequence that the FBTWC is continuous along northwestern Honshu
Island in summertime, while it degenerates along the coast between the Sado Strait and the Oga Peninsula in other seasons.
On the other hand, a mainstream of the SBTWC exists with meanders and eddies in the offshore region deeper than 1000 m to
the north of the Sado Island throughout the year. 相似文献
6.
Taketoshi Kodama Akihiko Morimoto Tetsutaro Takikawa Masashi Ito Yosuke Igeta Shoko Abe Ken-Ichi Fukudome Naoto Honda Osamu Katoh 《Journal of Oceanography》2017,73(6):759-769
To identify water with an excess nitrate concentration to phosphate ratio and its potential source, the nutrient concentrations in the Tsushima Strait (TSS) were investigated over ten cruises in August and September 2007–2014, excluding 2010. On the basis of the Redfield ratio, water with an excess nitrate concentration of >1 μM (positive ExNOx water) was identified below the surface mixed layer during four cruises in 2011–2013. Positive ExNOx water was present mainly in less-saline (<34) waters with a density of 22–25 σ θ , and 25–75 m depth. However, in August 2012, positive ExNOx was detected in dense (25–25.5 σ θ ) and deep (50–110 m depth) waters near the salinity maximum, although the salinity during this period was significantly lower than that in other years. The horizontal length of positive ExNOx water was >100 km across the TSS during two cruises in August 2012 and September 2013, respectively. According to multi-regression analysis conducted on the silicate concentration, temperature, and salinity, the silicate concentration was increased in the less-saline subsurface water. The required amount of original freshwater was 108–9 m3 day?1 based on the excess nitrate concentration. This evidence indicates that the positive ExNOx water originated from large river waters such as the Changjiang. Thus, discharged water from the rivers of the East Asia is contributing to the increased N:P ratio in the Tsushima Warm Current, southern Japan Sea. 相似文献
7.
The relations between the volume transport and the sea level difference across the Tsushima Straits have been investigated using current data provided by ADCP mounted on the ferry Camellia, plying between Hakata and Pusan. Empirical formulas to deduce the volume transports using the sea level differences across the eastern and western channels are proposed, considering the seasonal variation of the vertical current structure. The interannual variation of volume transport through the Tsushima Straits for 37 years from 1965 to 2001 is estimated using the empirical formulas. The total volume transport through the Tsushima Straits, averaged for 37 years, is 2.60 Sv and those of the eastern and western channels are 1.13 Sv and 1.47 Sv, respectively. The total volume transport through the Tsushima Straits tends to decrease with a roughly 15 year variation until 1992, then begins to increase. 相似文献
8.
Tetsutaro Takikawa Goh Onitsuka Ken-ichi Fukudome Jong-Hwan Yoon Akihiko Morimoto Masatoshi Moku Atsushi Watanabe 《Estuaries and Coasts》2011,34(4):775-784
Horizontal, vertical and temporal distribution of a cyclonic (counterclockwise) eddy, where biological productivity is high,
downstream of the Tsushima Islands in the eastern channel of the Tsushima Straits in November 2007 was revealed using conductivity–temperature–depth
and acoustic Doppler current profiler data. The eddy had a horizontal scale of approximately 40–60 km, and the accompanying
baroclinic current was more than 15 cm s−1 at the edge of the eddy. The island-induced cyclonic eddy moved east-northeastward at about 10 km day−1 (∼10 cm s−1) along the Tsushima Warm Current and was intensified by the barotropic instability in the current shear. The cyclonic eddy
with high surface chlorophyll a concentrations intensified in the vicinity of the Tsushima Islands and was advected by the Tsushima Warm Current towards
the southwestern Japan Sea. 相似文献
9.
Seasonal volume transport variation in the Tsushima Warm Current through the Tsushima Straits from 10 years of ADCP observations 总被引：2，自引：1，他引：1
Ken-Ichi Fukudome Jong-Hwan Yoon Alexander Ostrovskii Tetsutaro Takikawa In-Seong Han 《Journal of Oceanography》2010,66(4):539-551
The seasonal variation in the structure and volume transport of the Tsushima Warm Current through the Tsushima Straits is
studied using the acoustic Doppler current profiler (ADCP) data obtained by the ferryboat Camellia between Hakata, Japan and Pusan, Korea from February 1997 to February 2007. A robust estimation method to eliminate the effects
of aliasing and tidal signals more accurately leads to a significant increase in the volume transport in winter time compared
to the previously reported one by Takikawa et al. (2005) who analyzed this ADCP dataset for the first 5.5 years. The 10 years average of volume transport through the Tsushima
Straits is 2.65 Sv, and those through the channels east (CE) and west (CW) of the Tsushima Islands are 1.20 Sv and 1.45 Sv,
respectively, which represent a 13% increase and an 8% decrease from those of Takikawa et al. (2005). The transport through the CE increases rapidly from winter to spring and then decreases gradually as winter approaches.
On the other hand, the transport through the CW increases gradually from winter to autumn and then decreases rapidly as winter
approaches. The transport through the CE is larger than that of through the CW from February to April. The contribution of
the Ekman transport near the sea surface, which is not measured with the ADCP, to the seasonal volume transport variation
across our ADCP section is not significant. 相似文献
10.
Tidal currents in the Tsushima Straits have been analyzed using measurements obtained since February 1997 by an acoustic Doppler
current profiler (ADCP) mounted on the ferryboat Camellia. Tidal current constituents (M
2, S
2, K
1, O
1) are dominant among the ten tidal current constituents (Q
1, O
1, P
1, K
1, N
2, M
2, S
2, K
2, MSf, Mf), and generally 1.4–2.1 times stronger at the western channel of the straits than those at the eastern channel. The ratio
between amplitude of M
2, S
2, K
1 and O
1 averaged along the ferryboat track is 1:0.45:0.59:0.51. The major axis directions of tidal current ellipses are generally
SW to NE, exceptionally in the vicinity of the Tsushima Islands. Approaching the Tsushima Islands from the Korean Peninsula
side, the major axis gradually rotates clockwise. At the western channel, the M
2 and K
1 constituents change the rotation direction of current vectors from clockwise to counterclockwise at about 90–130 m depth.
The contributions of the tidal currents to the mean kinetic energy and the mean eddy kinetic energy along the ferryboat track
are, on average, 0.56 and 0.71, respectively. This suggests that tidal current activities are generally more dominant than
the mean current activities and much more dominant than eddy activities. The only region where the eddy activities are comparable
to the tidal current activities is located on the east side of the Tsushima Islands.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献