The Effect of Environmental Change on Biogenic Silica Temporal Variation in Sediments of the Northeastern South China Sea
Date Issued
2014
Date
2014
Author(s)
Tsai, Hsu-Pin
Abstract
Biogenic silica, as well as carbonaceous particles, are the most important types of biogenic sediments. For the South China Sea area where huge amount of terrigenous particles from small rivers of the surrounding islands and large rivers play a very important role in transporting land derived materials to the ocean, however, the exact amount of terrigenous materials from land to the ocean may subject to climate change and varied in times. In addition, sea temperature fluctuation may also affect ocean productivity in the area. There is little study on the variation(s) of sediment deposition with respect to the temporal variation, in particular, and area subjecting to climatic changes.
Biogenic sediments mainly compose of biogenic silica, organic carbon and calcium carbonate. Biogenic Silica (BSi) is the amorphous silicon content which is usually determined by wet chemical extraction. It is also known as or referred to as biogenic opal (Opal). Main sources of the biogenic silica in sediment come from diatoms, radiolarians, silicoflagellates and sponge spicules and other siliceous organisms, with their skeletons accumulated on the seabed. Biogenic silica content variation in sediments usually indicate a change(s) of oceanic paleoproductivity. Changes of paleoproductivity were closely related to the status of paleoseawater nutrient and the change of paleoclimatic condition. Hence, sedimentary record of biogenic silica could serve as an indicator of large scale changes of the ancient oceans or paleoclimatic (e.g. glacial or interglacial) change.
The result of this study showed that biogenic silica content in sediments in the northeastern South China Sea at sampling site AG (ssAG; Latitude: 20.05° N, Longitude: 118.10° E) range between 3.68% and 9.20%, with an average of 5.64 ± 1.92%, and at site 2914 (ss2914; Latitude: 22.03° N, Longitude: 119.85 ° E) range between 1.63% and 6.40%, with an average of 3.57 ± 1.47%. From the perspective of spatial scales, ssAG is further away from Taiwan compare to ss2914. ssAG has much higher level of biological source of sediment. The amount of biogenic silica in both ssAG and ss2914 are relatively low for Holocene and high during the last glacial. In between, the amount of biogenic silica correlate very well with the amount of organic carbon, especially in glacial period where R2 reach up to 0.70. This correlation is much weaker during Holocene.
In conclusion, large amount of suspended particles from Taiwan do play an important role in diluting biogenic sediments. During the last glacial and the transition period, siliceous shell was a major source of sediment organic carbons in the northeastern South China Sea’s sediments. The amount of biogenic silica in last glacial is relatively higher than in Holocene.
Subjects
南海
古氣候
末次冰盛期
生物矽
化學萃取
SDGs
Type
thesis
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