Deposition of Terrestrial Organic Materials from Small Mountainous Rivers on the Narrow Continental Shelf, Southwest of Taiwan
Date Issued
2008
Date
2008
Author(s)
Hsu, Feng-Hsin
Abstract
Huge amount of suspended materials together with organic carbon exported from Kaoping River, Tsengwen River and Erjen River could serve as a major carbon source and may influence biogeochemical carbon cycle in offshore area, southwest of Taiwan. However, little is know concerning fate of this terrestrial organic carbon. This study aims at understanding fate of this terrestrial organic carbon exported to the continental margin, offshore southwestern Taiwan through investigating spatial variations of organic carbon, organic nitrogen, grain size, and organic carbon isotopic compositions in surface sediments to evaluate net terrestrial organic carbon burial flux in the narrow continental shelf settings. Results show that surface sediments in offshore area, southwest of Taiwan were strongly influenced by terrigenous materials exported from Kaoping River, Tsengwen River and Erjen River. Organic carbon and nitrogen content in surface sediments increased from offshore Penghu island to offshore Kaoping River. Organic carbon and nitrogen content showed strong positive linear relationships with mud content, which indicates that grain size is one important factor in controlling distribution of organic carbon and nitrogen in this study region. The appearance of lighter organic carbon near Kaoping River, Erjen River and Tsengwen River mouth and gradually shifting from lighter at shelf to heavier at slope demonstrated that organic carbon are shifting from terrigenous domination to predominant marine away from the shore. Comparing to those predominantly terrigenous sediments near rivers , sediments offshore Penghu Island are characterized by mostly coarse-grained and biogenic in origin. Offshore Tsengwen and Erjen River are mostly silty to coarse-grained sediments with a major fraction composed of terrigenous sediments. Offshore Kaoping River were dominated by terrigenous fine-grained muddy sediments. In addition, patches of higher organic carbon with lighter isotopic compositions were found offshore north of the Kaoshiung Harbor, probably a result of organic pollutant from sewage outlets. Terrestrial organic carbon burial flux in our study area is 0.063 Mt/yr, which is only 12 % of the total particle organic carbon exported from Kaoping river, Erjen River and Tsengwen River. Higher fraction(>90%) of terrestrial organic carbon occurred in the lower Koaping Canyon indicates that a very important part of the terrestrial organic carbon exported from Kaoping River may transport directly into deep ocean through the Kaoping Canyon. Kaoping Canyon is playing a significant role in transportation and burial of terrestrial organic materials from the Kaoping River to deep ocean.
Subjects
Mountainous River
Terrestrial Organic Carbon
Kaoping Canyon
Type
thesis
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