南海東北部過去四萬年古海洋沉積作用和氣候變遷紀錄

Records of the Past 40k Years Sedimentation and Climatic Variations in the Northeastern South China Sea

施迎瑩(Ying-Ying Shih)

指導教授 ： 林曉武

國立臺灣大學/理學院/海洋研究所/碩士(2011年)

https://doi.org/10.6342/NTU.2011.10610

摘要

南海東北部周遭環繞台灣、菲律賓、中國大陸及許多小島，每年承接大量河川帶來之懸浮顆粒物質，沉積物之組成深受河川輸出陸源物質所影響；鈣質或矽質生物殼體沉降，也是另一種重要的沉積物來源。沉積物組成受到氣候、海平面狀態升降和陸海源物質輸入改變之影響，隨時序分布記錄下不同沉積環境的特徵。本研究利用海岩一號901航次活塞岩心採集器所取得南海東北部沉積物岩心，經由沉積物中浮游孔蟲C14定年結果重建沉積年代，以了解南海東北部過去約4萬年來古海洋環境及氣候變遷記錄。本研究亦分析沉積物中有機物質碳氮比值與有機碳、碳酸鈣、主要金屬離子含量及粒徑大小分布，來探討此段時間內沉積物來源變化及海域環境變遷影響機制。
研究結果發現南海東北部沉積物受古氣候變遷影響，大致上可分成下列三種沉積環境狀態：冰期（低海平面）、轉換期（海平面上升）及全新世（高海平面）。不同沉積環境下物質所表現的特徵也有所差異，冰期時沉積物陸源物質訊號增強，且出現粗顆粒物質沉積的頻率增加，碳酸鈣含量偏低；轉換期期間海平面上升，沉積物中特徵從陸源逐漸偏向海源，細顆粒物質含量逐漸遞增，主要離子受粒徑大小分布也隨之增加；全新世時期沉積物中海源物質訊號較強，碳酸鈣含量也約為冰期的兩倍，細顆粒物質含量也較冰期高；本研究結果顯示南海東北部沉積物組成受古氣候影響從冰期到間冰期由陸源物質沉積為主轉換成海源物質沉積。
沉積速率在南海東北部空間上之分布顯示研究測站於全新世時期，深受台灣小河傳輸陸源物質所影響。全新世氣候較溫暖且降雨量大，加上台灣小河山高水急懸浮顆粒輸出量大之特性，可藉由河川傳輸大量陸源物質至研究區域沉積；然而在過去冰期為低海平面狀態，沉積物中陸源物質訊號增強，顯示河川輸入陸源物質於冰期時可能有更重要之影響。

關鍵字

沉積環境 ； 南海東北部 ； 氣候變遷

並列摘要

Northeastern South China Sea receive particles from Taiwan, China, Philippines and other islands. Large amounts of terrigenous suspended sediments from the surrounding rivers control composition of sediments in the South China Sea. Another major source of sediment entering the South China Sea is the biogenic calcium and siliceous biogenetic particles. In addition to terrigenous and biogenic sediments, the type and amount of sediments may vary during glacial and interglacial transitions. Little data are available in addressing variations of particles entering the South China Sea during climatic changes and temporal variations.
The objective of this study is to verify if climatic and subsequent sea-level changed were recorded in the study area. Age model was constructed using AMS 14C dating over foraminifera in the sediment to delineate 400,000 years sedimentation and climatic variations in the area. This study also analyzed carbon and nitrogen ratio of organic matter in sediments, organic carbon, calcium carbonate content, major element compositions, and particle size distribution, to understand sources of sediment.
The results showed that sediments in the northeastern South China Sea strongly controlled by climate change. Based on their geochemical variations, the following three types of sedimentary environments can be identified : glacial (lower sea level), transition (sea-level rise) and Holocene (higher sea level). Each type of sedimentary environment showed different depositional pattern, with the glacial sediments (lower sea level) showing stronger terrigenous signal with more frequent of coarse particles, low calcium carbonate content, while the transition (sea-level rise) sediment showing a gradual trend from a more terrigenous type sediments to more biogenous sediment, more finer grain particulate matter, in accompany with less terrigenous major ions characters.
The Holocene sediments were deposited during higher sea level with a stronger biogenous signal, twice as much of calcium carbonate content than glacial period, more fine-grained substances.

並列關鍵字

Sedimentation ； Northeastern South China Sea ； Climatic variations

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sedimentation in the South China Sea : Changes since the last glaciations. SCIENCE IN CHINA