Institute of Earth Sciences, Academia Sinica, Taipei, TaiwanInstitute of Oceanography, National Taiwan University, Taipei, Taiwan

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22 Φεβ 2014 (πριν από 3 χρόνια και 6 μήνες)

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M
odern (<100 years) sedimentation in the Taiwan Strait
: Rates and pathways


Chih
-
An Huh
a
,
Hui
-
Ju Kao
a
, b
,

Jui
-
Kun Chiu
b
,

Char
-
Shine Liu
b
,

Chih
-
Chieh
-
Su
b

and

Saulwood Lin
b
,


a

Institute of Earth Sciences, Academia Sinica, Taipei, Taiwan

b

Institute of
Ocean
ography
, National
Taiwan

University,
Taipei
, Taiwan


Sixty
-
two gravity cores and 20 box cores collected from 10 cruises during
200
5
-
2008 onboard R/V
Ocean Researcher I

and
II

were analyzed for
210
Pb and
137
Cs
to estimate sedimentation rates and nuclide inv
entories. In addition, surficial
sediments from many of these cruises were analyzed for
7
Be and grain size
distribution. The results are integrated with information derived from Chirp sonar
survey about the structure and distribution
pattern

of shallow s
ediment strata to
elucidate the sources, pathways and budget of sediment in the Taiwan Strait from
seasonal to annual, decadal and centennial timescales.



Based on profiles of
210
Pb and
137
Cs
, the calculated s
edimentation rates largely
fall in the range f
rom 0.1 to 2.4 g cm
-
2

yr
-
1
, averaging 0.6 g cm
-
2

yr
-
1
. The highest
sedimentation rates as well as nuclide inventories are found at the top of the eastern
Yun
-
Chan Ridge near the Choshui River

s estuary and in the northwestern corner of
the Taiwan Strait.

In much of the Taiwan Strait, sedimentation rates are highly
variable with time, as indicated by non
-
steady state
210
Pb profiles. In the eastern part
of the strait, sedimentation rates appear to have increased in the last few decades,
probably reflecting

intensified soil erosion in Taiwan in wake of accelerated
exploitation of land and more frequent occurrence of intense precipitation in the
region.

On the other hand, in the northwestern part of the strait, sedimentation rates
appear to have decreased in

the last few decades
, which may be related to reduced
sediment supply to the Chinese coast from the Yangtze River
.



7
Be and grain size distribution in surface sediments, coupled with Chirp sonar
survey of shallow sediment strata, indicate that coarse san
d is distributed mainly
along part of the west coast of Taiwan and the Kuanyin depression
where the
accumulation of fine sediments

is limited by swift along
-
shore or bottom flows.

The
distribution of fine sand
and mud
in the Taiwan Strait is controlled ma
inly by tidal
currents which transport
fine sand

from the Yun
-
Chang Ridge northward toward the
middle of the Taiwan Strait where fine sand from the south merges into mud derived
from western Taiwan Rivers. As for the mud in the northwest of the Strait, it

is
derived from Chinese rivers and transported alongshore toward the south.


In summary, shallow (<1 m) sediments in the Taiwan Strait are composed of
relict sand and modern (<100 years) sediment derived mainly from Taiwanese rivers.
Dispersal and deposi
tion of such sediments are controlled by modern hydrodynamics
in the strait.