In this study, concentrations of organic biomarkers of core MD012404, recovered from central part of the Okinawa Trough, were analyzed, included of unsaturated alkenones and n-alkanes, for reconstructing paleoenviromental and paleoclimatic records for the past 100,000 years.
The unsaturated alkenone index of Uk¡¬37 were calculated for reconstructing past variations of sea surface temperature (SST) in the East Chna Sea (ECS). Through the past 100,000 years, our record revealed that the varied pattern of paleo-SSTs of the ECS was mainly reflecting Interglacial/Glacial cycles. This result indicates that the enhanced East Asian winter monsoon which is induced by the changing orbital forcing is the dominant controlling factor to influence the hydrological conditions in the ECS. Otherwise, except of the warming event of Bølling-Allerød and cooling event of Younger Dryas, no obviously cooling trends were observed in the record indicating that the Uk¡¬37 based SST was not sensitive to the millennial-scaled climate events. This may be caused by the slow response of the SST to the millennial-sclaed events. The concentrations of unsaturated alkenones reconstructed in this study can represent to the surface productivity of the ECS. Our record shows that the values are higher in glacial period than in interglacial period. The higher productivity observed in glacial period may result from the wind-driven water mixing. Therefore, the well-mixing of surface and subsurface water thus can supply higher nutrients upto the surface water than induce the higher productivity in glacial period in the ECS. However, a more complicated pattern is found in MIS 5, the unsaturated alkenones have extremely high values in this interval which is different to the Holocene even though that the climatic conditions and global sea level are similar in these two periods. These high values may be caused by either higher surface production or well preservation, which results from the pool ventilation in the ECS.
In addition, distributed pattern of n-alkanes can represent to the possible sources of organic materials and vegetation changes on land. Our record shows that n-C31 alkane is dominant in n-alkanes, and the distribution pattern of n-alkanes (C31 > C29 > C33 > C27 > C25 ) is similar to the sediments discovered on the continental shelf of ECS and the estuary of the Changjiang River and is different with the sediments from the Lanyang Hsi River. This fact indicates that the organic materials buried in sediments of the Okinawa Trough are mainly contribute from the ECS continental shelf and the Changjiang River is serves as the main contributor of terrestrial sediments in the study region. Our calculated Carbon preference index (CPI) indicates that terrigenous orangic matters are less influenced by degradation and diagenesis in glacial period, especially during LGM, and the changing pattern is highly correlated with the global sea level changes. Lower sea level observed in glacial period shorten the transporting distance of sediments from the Changjiang River to the Okinawa Trough thus causes more terrestrial inputs and deposits in the Okinawa Trough.
| Identifer | oai:union.ndltd.org:NSYSU/oai:NSYSU:etd-0914110-084903 |
| Date | 14 September 2010 |
| Creators | Yang, Yung-hua |
| Contributors | Hung-yu Chen, Yuan-pin Chang, Cheng-wei Fan |
| Publisher | NSYSU |
| Source Sets | NSYSU Electronic Thesis and Dissertation Archive |
| Language | Cholon |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.lib.nsysu.edu.tw/ETD-db/ETD-search/view_etd?URN=etd-0914110-084903 |
| Rights | unrestricted, Copyright information available at source archive |
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