Data Al
Resume:
Journal of Oceanography, Vol. **, pp. *** to ***, 2010
Review
Review on Current and Seawater Volume Transport
through the Taiwan Strait
J IANYU HU 1,2*, HIROSHI KAWAMURA2, CHUNYAN LI 3,4, H UASHENG HONG1 and Y UWU J IANG1,2
1
State Key Laboratory of Marine Environmental Science, College of Oceanography and
Environmental Science, Xiamen University, Fujian 361005, China
2
Center for Atmospheric and Oceanic Studies, Graduate School of Science, Tohoku University,
Sendai 980-8578, Japan
3
Department of Oceanography and Coastal Sciences, Coastal Sciences, School of the Coast and
Environment, Louisiana State University, Baton Rouge, LA 70803, U.S.A.
4
College of Marine Sciences, Shanghai Ocean University, Shanghai 201306, China
(Received 30 September 2009; in revised form 27 July 2010; accepted 29 July 2010)
Patterns and features of currents and seawater volume transports in the Taiwan Strait Keywords:
Review,
have been reviewed by examining the results from more than 150 research papers in
current pattern,
recent decades. It is noted that there are diverse or even conflicting viewpoints on
seawater transport,
these subjects. Here both common and different opinions are summarized. This re-
Taiwan Strait,
view paper covers the studies involving in situ measurements and numerical modeling
winter,
of current velocity, analyses of hydrographic data, and classification of water masses.
summer.
Generally speaking, there are three currents in the Taiwan Strait: the China Coastal
Current along the Fujian coast in the western Taiwan Strait, the extension of the
South China Sea Warm Current in the western and central Taiwan Strait, and the
Kuroshio s branch or loop current intruding through the eastern Taiwan Strait. The
current pattern in winter is quite different from that in summer, and the currents
also exhibit differences between the upper and lower layers. The seawater volume
transport through the Taiwan Strait is about 2.3 Sv northward in summer but about
0.8 Sv northward in winter. Both the current pattern and the seawater transport vary
with local winds in the Taiwan Strait. This is particularly true in winter when the
currents and the transport in the upper layer are significantly affected by strong
northeasterly winds.
1. Introduction tends between the Penghu Islands and the Zhang-Yun
The Taiwan Strait, located between the South China Ridge (or Changyun Rise, Chang-yuen Ridge in some
Sea (SCS) and the East China Sea (ECS), is an important references) from the Penghu Channel.
channel for seawater transport. It connects with the Luzon The Taiwan Strait is in a subtropical monsoon re-
Strait on its southeastern side. gime. According to its climatological features, summer
As shown in Fig. 1, the Taiwan Strait is character- is usually from June to August, while winter is from De-
ized by variable bottom topography even though the depth cember to February. Northeasterly winds prevail in the
is about 60 m for the most part. A shallow bank, i.e. the Taiwan Strait in winter; and the frequency of northeast-
Taiwan Bank, is located in the southern Taiwan Strait with erly winds reaches 58% with an average wind speed of
10.2 m s 1. In summer, southwesterly and southerly winds
a depth of less than 30 m. In the southeastern Taiwan
Strait, the deep Penghu Channel lies along the southwest- dominate in the Taiwan Strait with a frequency of 45%
and a mean speed of 5.1 m s 1 (Ke and Hu, 1991). There-
ern coast of Taiwan Island and the Pengbei Channel ex-
fore, the wind-driven currents are mostly southwestward
in winter but northeastward in summer, though their wind-
* Corresponding author. E-mail: abpnzo@r.postjobfree.com driven properties have not been observed in detail. The
difficulty in observing the wind-driven component is due
Copyright The Oceanographic Society of Japan/TERRAPUB/Springer
5 91
Yuan (2005), Sun (2006) and Liu et al. (2008) summa-
rized the circulation dynamics in the coastal oceans near
China and in the SCS. Isobe (2008) reviewed the recent
advances in ocean circulation research in the Yellow Sea
and the ECS continental shelves. However, these papers
did not elaborate sufficiently on the current patterns and
seawater volume transport in the Taiwan Strait.
In summarizing more than 150 articles in this field,
it is evident that there are several viewpoints on current
patterns and seawater transport through the Taiwan Strait.
The purpose of this paper is to provide a comprehensive
summary of these studies. Sections 2 and 3 give reviews
on the current patterns and seawater transport, respec-
tively. And a summary with some discussions is given in
Section 4.
2. Current Patterns in the Taiwan Strait
2.1 Early viewpoints on current patterns
Early studies on the current patterns in the Taiwan
Strait were usually based on the following data sources:
(1) the current charts published by the Japanese Hydro-
logical Office in 1925; (2) the current vectors derived from
ship drift; (3) the measured current data from the Chi-
nese National Comprehensive Oceanographic Survey
Fig. 1. Map of the Taiwan Strait and its adjacent seas, with
(1958 1960) (Guan and Chen, 1964); and (4) tempera-
depth contours in meters. PT, XM, DS, NA, ST, ZYR, PBC,
ture and salinity distributions from a few oceanographic
PH, PHC and TB denote Pingtan, Xiamen, Dongshan, Nan-
observation cruises. Moreover, these early studies were
ao, Shantou, the Zhang-Yun Ridge, the Pengbei Channel,
mostly associated with studying the current systems in
the Penghu Islands, the Penghu Channel and the Taiwan
the ECS (such as Japanese Hydrological Office, 1925;
Bank, respectively.
Uda, 1934; Nino and Emery, 1961; Chu, 1963, 1971; Guan
and Chen, 1964; Nitani, 1972). As a typical early under-
standing of the currents in the Taiwan Strait, the monsoon
to the fact that the currents are also strongly affected by system was regarded as the primary force causing the flow
other components from both the northern SCS and the variations around Taiwan (Wyrtki, 1961).
Luzon Strait. An important study was conducted by Nitani (1972)
It has been accepted that the Taiwan Strait has sev- who described the surface currents around Taiwan both
eral major currents, i.e. the China Coastal Current, the in summer and in winter. It was indicated that a coastal
extension of the South China Sea Warm Current (SCSWC) current flows southwestward in winter but northeastward
(Guan, 1998, 2002; Guan and Fang, 2006) and the intru- in summer in the western Taiwan Strait. In the eastern
sion from the Kuroshio. Affected by monsoon winds, the Taiwan Strait, the current flows northeastward in both
currents demonstrate great seasonal variations. Especially, summer and winter seasons. This was the early viewpoint
the China Coastal Current in the western Taiwan Strait is on current patterns in the Taiwan Strait. Combining the
considered as the southwestward Zhemin Coastal Cur- charts from Nino and Emery (1961) and Nitani (1972),
rent in winter but the northeastward Yuedong Coastal Jan et al. (2002) summarized the current patterns as shown
Current in summer, which appears to be associated with in Fig. 2, specifying that the current in the western Tai-
the monsoon winds. wan Strait is the China Coastal Current (i.e. the Zhemin
The study on the currents and seawater volume trans- Coastal Current) in winter and the SCS surface current in
ports in the Taiwan Strait has been conducted for dec- summer. In contrast, the current in the eastern Taiwan
ades. Hu et al. (2000) and Hu et al. (2003) reviewed the Strait is the Kuroshio branch current.
SCS circulation and the Taiwan Strait upwelling, respec- As indicated in the following sub-sections, these
tively. Wang (2000), Liu et al . (2002) and Xiao et al . early viewpoints on the current patterns were too simpli-
(2002) described the hydrographic features in the Taiwan fied. For example, they did not represent currents in the
Strait. Su (2001, 2004), Wang G. H. et al. (2003), Su and central Taiwan Strait.
5 92 J. Hu et al .
Fig. 2. Summarized early viewpoint of current patterns in the Taiwan Strait in (a) summer and (b) winter (cited from Jan et al.,
2002 after Nino and Emery, 1961 and Nitani, 1972). In (b), the China Coastal Current may include the Zhemin Coastal
Current.
2.2 Modified viewpoints on current patterns in the 1980s exists a northeastward current, the Taiwan Warm Current,
In the 1980s, many hydrographic surveys were con- in the southern ECS. As shown in Fig. 3(b), it is clearly
ducted in the Taiwan Strait by several oceanographic and indicated that these two warm currents connect with each
fishery institutions in China (e.g., Fan, 1982; Qiu et al., other in the Taiwan Strait in summer. In contrast, there
1985; Chuang, 1985, 1986; Wang and Weng, 1987; Weng was not enough evidence to link these two currents in the
et al., 1987, 1988; Xiao and Cai, 1988; Li and Li, 1989; central Taiwan Strait in winter (Fig. 3(a)) though such
Wang, 1989). The observational data from these surveys link had been hypothesized. Guan (1986b) argued with
urged modifications to the earlier viewpoints on the cur- more evidence that the SCSWC extends northeastward
rent patterns in the Taiwan Strait. and flows through the central Taiwan Strait even in win-
At the beginning of the 1980s, Wu (1982a, 1982b, ter. During the 1980s, several other studies (e.g., Ma,
1983) studied the currents in the Taiwan Strait. On con- 1987; Su and Wang, 1987; Fang and Zhao, 1988) pre-
structing a current system in the China Seas, Guan (1986a) sented the possible mechanism for such a warm current
proposed a conceptual current pattern in the Taiwan Strait system.
(Fig. 3), in which three currents appear in the Taiwan Strait
in summer as well as in winter. One current flows south- 2.3 Further modified viewpoints on current patterns in
westward in winter but northeastward in summer in the the 1990s
western Taiwan Strait. Another current was suggested to A better understanding of the current patterns in the
originate from the Kuroshio and flow northward in the Taiwan Strait was given in the 1990s by intensive in situ
eastern Taiwan Strait (Fan, 1982; Guan, 1985). Between current observations (e.g., Hong et al., 1991; Li and Liang,
both currents, a northeastward current exists in the cen- 1991; Fang et al., 1992; Weng et al., 1992, 1993; Wang
tral Taiwan Strait in summer and was supposed to appear and Chern, 1992, 1993; Chen and Tang, 1993; Huang et
in winter as well. al., 1993; Fang, 1995; Xu et al., 1995; Wang, 1995; Xu
As revealed by Guan and Chen (1964) and Guan and Su, 1997; Chen et al ., 1999; Hu et al., 1999a, b, c)
(1978a, b), there exists an SCSWC offshore of the and numerical model studies (e.g., Li et al., 1993; Jan et
Guangdong coast, which flows northeastward all the year al., 1994a, 1994b, 1998; Lu et al., 1997; Wang and Yuan,
round. It should be noted that the SCSWC flows against 1997a, b; Cai and Wang, 1997; Cai et al., 1998a, b).
the prevailing northeasterly wind in winter. There also Using the measured current data at several day-night
R eview on Taiwan Strait Current and Seawater Transport 593
Fig. 3. Modified current patterns in the Taiwan Strait and its
adjacent seas in (a) winter and (b) summer (redrawn after
Guan, 1986a). In (a), a is the Kuroshio; b, the Tsushima
Warm Current; c, the Huanghai Sea Warm Current; d, the
Bohai Sea Circulation; e, the Taiwan Warm Current; f, the
China Coastal Current; g, the SCS Warm Current; and h,
the West Korea Coastal Current. The portion of the China
Coastal Current along Zhejiang and Fujian coasts is the
Zhemin Coastal Current.
anchored stations, Hu et al . (1990) proposed a schematic
wintertime current pattern in the Taiwan Strait (Fig. 4). It
was indicated that there is a coastal current flowing south-
southwestward along the Fujian coast with a width of
about 40 km and a mean speed of about 0.45 m s 1. It is
stronger in the north of the Taiwan Strait, and then be-
comes weaker as it heads south-southwestward (Fig. 4(a)).
The coastal current, with low temperature and low salin-
ity water, is originated from the Zhemin Coastal Current
(one part of the China Coastal Current, see Fig. 3(a)) and
was reported to reach the area near Dongshan (Zeng, 1986;
Xiao and Cai, 1988; Guan, 1994), where the low tem-
perature and low salinity water was still seen in the sur-
face layer in winter. However, the Zhemin Coastal Cur-
rent could not affect as far-away as the southwestern Tai-
wan Strait in the intermediate layer or near-bottom layer
(Figs. 4(b) and (c)). The measured data also showed an
upwind current flowing northeastward in the central Tai-
wan Strait (Fig. 4), with a relatively warmer and saltier Fig. 4. Schematic wintertime current patterns in the Taiwan
water mass from the northern SCS. In the southern and Strait (redrawn after Hu e t al ., 1990). (a) Surface layer,
southeastern areas of the Taiwan Strait, a current changes (b) intermediate layer, and (c) near-bottom layer. The vec-
direction from northwestward in the southwest of Taiwan tors in the figures are from the in situ current measurements.
to southwestward in the south of Taiwan Bank (Fig. 4), The dashed long arrows denoted by A, B, C and D at the
which was regarded as the right flank of the SCS Branch arrow-head are the schematic current patterns deduced from
the measured currents.
of Kuroshio (SCSBK) (Qiu et al., 1985).
5 94 J. Hu et al .
Fig. 5. Schematic summertime current patterns in the southern Taiwan Strait (redrawn after Hu and Liu, 1992). (a) Surface layer,
(b) intermediate layer, and (c) near-bottom layer. The solid vectors are from the in situ current measurements; the dashed long
arrows denoted by A, B and C at the arrow-head are the schematic current patterns deduced from the measured currents; and
the double-arrows in (a) denote the flank of the Kuroshio s loop current in summer.
R eview on Taiwan Strait Current and Seawater Transport 595
With more measurements, Hu and Fu (1991) sum- ter and summer, and shows that the SCSWC extends to
marized the wintertime current patterns in the southern the Taiwan Strait both in winter and in summer (Figs. 4
Taiwan Strait. The currents in the surface, intermediate and 5). In addition, Guan (1986a) suggested a combina-
and near-bottom layers are similar to those in the south- tion of the SCSWC and the Taiwan Warm Current through
ern part of Fig. 4. In the surface layer, there is a the Taiwan Strait. Sun et al. (1996a) collected previous
northeastward upwind current in the western and central current charts (e.g., Institute of Marine Scientific and
Taiwan Strait with a speed of about 0.25 m s 1. In the Technological Data and Information of SOA, 1978, 1982;
near-bottom layer, it flows northeastward (Wang and Guan, 1986b; Chen, 1992) and sea-bed drifter observa-
Weng, 1987; Weng et al., 1990). This current was con- tions (Zhang et al., 1991), and indicated that northward
sidered to be from the sea off Guangdong as an extension and northeastward currents are dominated in the layer
of the SCSWC. Qiu et al . (1985) and Guo et al . (1985) beneath 10 m in the Taiwan Strait and these currents merge
proposed that the SCSBK enters the northeastern SCS with the Taiwan Warm Current after flowing out of the
through the Luzon Strait in winter, forming a cyclonic northern Taiwan Strait, but the surface currents in the
meander with a width of about 130 km and a surface speed Taiwan Strait are affected by local winds. Sun e t al .
of about 1.0 m s 1. Its right flank sweeps over the south- (1996b) summarized the warm current system in the ECS
ern Taiwan Strait. While the SCSBK enters the northeast- and SCS and named it the continental shelf warm cur-
ern SCS, the Kuroshio has another branch flowing north- rents in the East China Sea and South China Sea . This
ward along the western coast of Taiwan. In situ measure- concept pictures the SCSWC as flowing through the Tai-
ments (Fan and Yu, 1981; Wu, 1982a; Wang and Chern, wan Strait in both summer and winter. However, some
1988; Hu et al ., 1999a) and remote sensing observations studies suggested a slightly more complicated current
(Chen, 1983; Xiu and Chen, 1987; Lin et al., 1992) sup- system in the northern Taiwan Strait, e.g., the Zhemin
ported the idea that the Kuroshio may have one branch Coastal Current could have a branch intruding the cen-
entering the eastern Taiwan Strait and its warmer and tral Taiwan Strait in winter (Weng et al., 1988; Wang and
saltier water may reach 24~26 N. Chern, 1989).
Hu and Liu (1992) collected in situ current vectors In the 1990s, several numerical model studies on the
in summer, and analyzed the summertime currents in the currents in the Taiwan Strait and its adjacent seas were
southern Taiwan Strait (Fig. 5). In the western sea area, conducted, focusing on mechanisms for these currents.
there exists a northeastward current from the surface layer Jan et al. (1994a, b) used a three-dimensional baroclinic
to near-bottom layer and flows all the way through the ocean circulation model to study influences of the Chang-
western Taiwan Strait. This current could be traced back yuen Ridge and wind stress on the summertime currents
to the SCSWC and was considered as the SCSWC s ex- in the Taiwan Strait. Using a barotropic numerical model,
tension in the Taiwan Strait. This extension is affected Cai and Wang (1997) studied the effects of wind stress
by the Yuedong Coastal Current (Qiu et al ., 1985) on its and the Kuroshio on the circulation of the northeastern
inshore side so that it is sometimes characterized by high SCS and the Taiwan Strait. They indicated that the circu-
temperature and low salinity water in the surface layer. lation in the Taiwan Strait is mainly affected by wind,
On the offshore side of this extension, another bottom topography and the Kuroshio, and that the
northeastward current flows side by side in the southwest Kuroshio plays an important role in the formation of the
of Taiwan Bank, which subsequently turns eastward while SCSBK, the wintertime SCSWC and the Taiwan Warm
bifurcating into two branches in the southwest of Taiwan Current. Cai et al. (1998a, b) further examined the roles
(Fig. 5). One of the branches flows out of the SCS through of the Kuroshio, wind stress and bottom topography on
the northern Luzon Strait, and the other flows northward the circulation in the Taiwan Strait through developing a
along the western coast of Taiwan. Qiu et al. (1984, 1985) barotropic and baroclinic coupled model. Wang and Yuan
and Li and Wu (1989) proposed that the Kuroshio intrudes (1997a, b) used three-dimensional diagnostic models to
the SCS in a loop form in summer, which means that the compute the currents in the Taiwan Strait in summer. Jan
summertime SCSBK enters the SCS through the south- et al. (1998) simulated the wintertime circulation in the
ern Luzon Strait as flowing westward, and then turns anti- Taiwan Strait. However, these models in the 1990s had
cyclonically in the east of Dongsha Islands to flow through relatively low spatial resolutions or small computational
the northern Luzon Strait and back to the Kuroshio main domains though they contributed to further advancement
path. It is clear that the left flank of the northern SCSBK of understanding the mechanisms for the circulation in
loop could affect the southern Taiwan Strait in summer the Taiwan Strait.
(Fig. 5).
These findings on current patterns focus on the south- 2.4 Recent progress in studying current patterns since
ern Taiwan Strait, which indicates that the SCSBK af- 2000
fects the southern Taiwan Strait in different ways in win- Recent progress in understanding the current patterns
5 96 J. Hu et al .
Fig. 6. Schematic charts showing the Taiwan Strait circulation in (a) winter, (b) spring, (c) summer and (d) fall (autumn). The
thick and short-dashed line marks the outer edge of Changyun Rise (cited from Jan et al ., 2002).
has been made with increasing observations using ship- several advanced numerical models in the Taiwan Strait
borne Acoustic Doppler Current Profiler (sb-ADCP), bot- and its adjacent seas (e.g., Chern and Wang, 2000; Chu
tom mounted ADCP (bm-ADCP) and mooring systems and Li, 2000; Xue et al ., 2001; Jan et al., 2002, 2010; Lo
in the Taiwan Strait (e.g., Tang et al., 2000; Lin et al., and Wang, 2002; Liang, 2002; Ren et al., 2002; Lu and
2002, 2005; Liang et al ., 2003; Wang et al ., 2004), and Sha, 2003; Fang et al., 2003, 2005; Wu and Hsin, 2005;
R eview on Taiwan Strait Current and Seawater Transport 597
(a) (b)
Fig. 7. Composite of sb-ADCP current velocity vectors at 30 m depth around Taiwan. (a) and (b) are for the southwesterly and
northeasterly monsoon season, respectively (cited from Liang et al., 2003).
Jiang, 2007; Jiang et al., 2007; Wu et al., 2007). The ocea- northward intrusion of the SCS Current in summer is rela-
nographers on the eastern side of the Taiwan Strait have tively unimpeded by the Chang-yuen Ridge; only the near-
made contributions to a further understanding of the cur- bottom flow is deflected anti-cyclonically. The Zhemin
rent patterns through several big research projects such Coastal Current does not enter the Taiwan Strait from the
as TSNOW (Nowcast System for the Taiwan Strait) (Jan north in summer (Fig. 6(c)). The autumn (fall) pattern is
et al., 2001) and SWEET (Strait Watch on the Environ- similar to the summer one, except for the emergence of
ment and Ecosystem with Telemetry) (Chen, 2004). the Zhemin Coastal Current in the northwestern Taiwan
Using a numerical model and the data from Strait (Fig. 6(d)). Especially for the winter season, their
hydrographic surveys and SST imagery, Jan et al. (2002) results clearly showed that the Zhemin Coastal Current
studied the seasonal variations of circulation in the Tai- intrudes into the central Taiwan Strait, which was previ-
wan Strait (Fig. 6). They indicated that: in winter, the ously proposed by Wang and Chern (1989) and confirmed
northward intrusion of the Kuroshio-sourced water in the by He et al. (1999) and Hu et al. (1999a) using in situ
eastern Taiwan Strait is blocked by the northeasterly current measurements and CTD data. Moreover, Jan et
monsoon, and the southward penetration of the China al. (2002) showed the Kuroshio s intrusion into the east-
Coastal Current (i.e. the Zhemin Coastal Current in the ern Taiwan Strait, while branching northwestward through
Taiwan Strait) reaches its maximum, but a portion of it is the Pengbei Channel. The circulation pattern around the
deflected by the Chang-yuen Ridge and turns back Penghu Channel was verified later by some ADCP obser-
northeastward (Fig. 6(a)). In spring, relaxation of the vations of Wang et al. (2004) and Lin et al. (2005). Wang
northeasterly monsoon unleashes the northward intrusion et al. (2004) carried out a field survey with sb-ADCP
of the Kuroshio-sourced water, and the Zhemin Coastal across the Penghu Channel, the gate of Taiwan Strait, in
Current retreats northward (Fig. 6(b)). With the aid of May 1999, and observed a uniform northward current in
summer stratification and the southwesterly monsoon, the the Penghu Channel with an average velocity of 0.73
5 98 J. Hu et al .
Fig. 8. Circulation and temperature distribution in the Taiwan Strait from a high resolution model (cited from Wu et al., 2007).
(a) in summer at 20 m depth, (b) in summer at 50 m depth, (c) in winter at 20 m depth, and (d) in winter at 50 m depth. Time
averaging for summer is over the period from June to August, while that for winter is over the period from October to
February of the following year. Velocity scales are in m s 1, and temperature contour interval is 1 C.
m s 1. Evidently, the current patterns proposed by Jan et of the Kuroshio. Figure 7 depicts the current patterns in
al. (2002) made good progress on the circulation study in the 30 m layer of the Taiwan Strait and its adjacent seas
the Taiwan Strait. However, since their model domain was during the southwesterly monsoon season (summer) and
limited to the major part of Taiwan Strait itself, the re- the northeasterly monsoon season (winter). It shows that
sults did not well represent the current patterns in the the Kuroshio intrudes into the eastern Taiwan Strait and
southwestern Taiwan Strait, and neither was the influence flows northward along the coast in both seasons, and that
of SCSWC considered in their model. its branch flows northwestward through the Pengbei
Using sb-ADCP data during 1991~2000, Liang et al. Channel. However, using satellite SST data and in situ
data such as hydrographic and 18O observations, Chen
(2003) studied the upper-ocean ( 3.0
difficulty in observing the wind-driven component is due
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