Modern sedimentation in the northern Taiwan Strait: Rates andathways
Date Issued
2009
Date
2009
Author(s)
Kao, Hui-Ju
Abstract
Sixty-two gravity cores and 20 box cores collected from 10 cruises onboard R/V Ocean Researcher I and II were analyzed for 210Pb and 137Cs to estimate sedimentation rates and nuclide inventories. In addition, surficial sediments from many of these cruises were analyzed for 7Be and grain size distribution. The results are integrated with information derived from Chirp sonar survey about the structure and distribution trend of shallow sediment 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 210Pb and 137Cs, the calculated sedimentation rates largely fall in the range from 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 210Pb 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. 7Be and grain size distribution in surface sediments, coupled with Chirp sonar survey of shallow sediment strata, indicate coarse sand is distributed mainly along part of the west coast of Taiwan and the Kuanyin depression with swift along-shore or bottom flows. The distribution of fine sand in the Taiwan Strait is controlled mainly by tidal currents which transport such particles 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 deposition of such sediments are controlled by modern hydrodynamics in the strait.
Subjects
Taiwan Strait,
sedimentation rate,
210Pb
137C
7Be
grain size analysis
Type
thesis
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