HIGH-RESOLUTION RECORDS OF BIOGENIC COMPONENTS AND THEIR PALEOCEANOGRAPHIC IMPLICATIONS IN THE UPWELLING AREA OF THE SOUTH CHINA SEA OFF EASTERN VIETNAM OVER PAST 480 ka
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摘要: 南海西部越南岸外MD05-2901孔沉积物分析显示,该孔覆盖氧同位素1-12期,底界年龄约为48万年。生源组分记录显示表层古生产力冰期高、间冰期低,体现间冰期海平面下降、陆源物质输入增强的影响。生产力在末次冰期达到最高,体现末次盛冰期海陆差异增强,东北风发育对生产力提高的促进作用。碳酸钙含量变化呈现冰期早期含量低、冰消期和间冰期含量高的趋势。其冰消期的高值在MIS1/2、MIS3/4和MIS5/6分界处,与浮游有孔虫碳同位素低值对应,揭示该地区的碳酸钙沉积旋回是"稀释旋回"。同时碳酸钙含量变化领先于同一地区浮游有孔虫氧同位素的变化,证明低纬海区碳酸钙泵作用对大气二氧化碳浓度和温度有影响。滤波分析结果显示碳同位素存在23 ka的岁差周期和偏心率长周期,生源组分的含量变化显示出典型的岁差周期,体现南海季风环流的轨道响应,证明低纬热带过程是调节气候变化的重要因素。Abstract: Based on the study of sediment samples from core MD05-2901 which is in the upwelling area in the South China Sea off eastern Vietnam, we obtained high-resolution records of biogenic components over the past 480 000 years. The records provide us paleoproductivity and paleoceanographic information associated with East Asian monsoon system. There were high total organic carbon (TOC) and high biogenic opal content during the glacial periods, and low TOC and low biogenic opal content occurred during interglacial periods. This indicates the intensified terrigenous sediment input during glacial periods, which is due to the low sea level. Particularly, both the TOC and biogenic opal content reached their maximum values during the last glacial period, which shows high productivity in this area caused by the strong northeast wind during the last glacial maximum (LGM). The variation of carbonate concentration displayed opposite trend to TOC and opal, and high value occurred during the deglaciation periods, indicating that CaCO3 cycle in this area was influenced by terrigenous dilution and the effect of "Carbonate pump" caused the high CaCO3 content during deglaciation periods. Moreover, the variations in paleoproductivity proxies exhibit a distinct cyclicity with a frequency of nearly 23 000 years, mainly responding to precession cycles, suggesting an influence of low latitude process, such as the monsoon climate in the South China Sea.
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Keywords:
- biogenic sediments /
- paleoproductivity /
- orbital-forcing /
- South China Sea
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