The fate of sediments in the Taiwan Strait: A
reassessment
Chih-Chieh Su1 (+886-2-33661391; donccsu@ntu.edu.tw)
Man-Shan Chang1
Horng-Ru Liao1
Ho-Shing Yu1
1
Institute of Oceanography, National Taiwan University, No.1, Sec. 4, Roosevelt
Road, Taipei 106, Taiwan
Taiwan Strait which located between Taiwan and southeast Mainland China is a
passage connecting the East and South China Seas. It is more than 300 km long and
varies in width with 160 km in the north to 200 km in the south, while its main water
body is relatively shallow (<60 m) and flat (Boggs et al., 1979). Several complex
bathymetric features such as the Kuanyin Depression, the Wuchu Depression, the
Changyun Ridge, the Penghu Channel, and the Taiwan Banks spread from north to
south in the Taiwan Strait.
For a long time, the sediments in the Taiwan Strait were considered as the relict
sediments which are wide spread on the continental shelves (Nino and Emery, 1961;
Chen and Chen, 1971; Boggs et al., 1974, 1975, 1979). Swift et al. (1971) reviewed
the evidence from the literature and brought up the name “palimpsest sediment” to
describe the relict sediment which influenced by the modern hydraulic regime.
Recently, some researchers reconsidered the so-called “relict sediment” in the Taiwan
Strait and postulated them as the modern tidal deposition systems (Liu et al., 1998;
Liao and Yu, 2005; Liao et al., 2008).
Over 50 surface sediment samples and 8 box cores were collected in the Taiwan
Strait. Grain size analysis, in conjunction with X-ray radiographs and 210Pbex dating
results, have been used to identify the sources, transportations and deposition of the
sediments. The grain size results from the box cores which collected from the
Kuanyin Depression varies from very fine sand in the south to medium silt in the
north. Comparing the grain size of coarse grain samples from the Kuanyin Depression
with the samples collected from Changyun Ridge implied the coarse sediments were
mainly from the Changyun Ridge. The trend analysis of the sediment grain size from
the Changyun Ridge also supported that the sediment were transport from southwest
to northwest (Liao, 2006). Despite the coarse portion of the sediments, the frequency
distribution histograms of the sediments also show a northward increase of the fine
grain sediments in this area. The size distribution of fine grain sediments were similar
to the surface sediments collected from the mouth of the Chosui River and implied
these fine grain sediments may coming from the Chosui River after the flood events
(Milliman et al., 2007).
Comparing the sedimentation rates which calculated from the 210Pbex and 137Cs
profiles, the sedimentation processes in the Taiwan Strait are mainly controlled by the
mixing process. This inference is also supported by the existing of large to very large
sand waves occur on the western Changyun Ridge and the channel which located at
the east side of the eastern Changyun Ridge.
In summary, the Taiwan Strait may be considered as a modern tidal deposition
system and the sediments in the central Taiwan Strait is composed by the coarse
sediments from the Changyun Ridge and the fine sediments from Taiwan.