摘要
提供了三万年以来草海沉积物有机质的δ13C记录。研究结果表明 ,草海沉积物有机质含量主要由岩性控制。一般粘土的有机质含量仅5 %左右 ,而纯泥炭的有机质含量在90 %以上。泥炭的δ13C值很低 ,而棕色粘土有机碳的δ13C值相对较高。一般认为 ,任何植物体的碳同位素组成主要与光合作用的C3和C4两种碳固定途径有关。C3类植物的δ13C值为 -26‰左右 ,而C4类植物大约为 -13‰。C3类植物在低温、潮湿的地区占有优势 ,而C4类植物适应既干旱又高温的气候条件。气候的变化改变C4和C3植物比例 ,从而改变沉积物有机质的δ13C值。由于C3和C4植物的平衡取决于温度和湿度两个因子 ,沉积物有机质δ13C曲线的解释比较复杂。研究结果证实 ,草海盆地不同地区分布的泥炭层 ,确实是间隙性构造隆升的产物 ,泥炭层特征的低δ13C值与气候变化的关系不大。草海盆地的δ13C值剖面和印度南部高沼地泥炭的δ13C记录对古气候变化的响应正好相反。印度南部的δ13C记录与气候干湿变化有很好的相关性 ,气温较高又潮湿的夏季风盛行时期对应低δ13C值。而草海柱样中气温较高时期对应高δ13C值。这两种情况都可以用C3和C4植物适应不同气候条件来解释。草海ZHJ柱样的δ13C记录显示 ,夏季风在早全新世之初达到最盛 ,中全新世减弱。
A δ13C record of the organic matter in lacustrine sediments spanning the past 30 000 a from Lake Caohai is presented in this paper. It is shown that the content of the organic matter in lacustrine sediments of the core ZHJ ismainly controlled by the lithology. The content of the organic matter in layersof clay usually is around 5%, while in pure peats it is more than 90%. The δ13C values of the peats are very low, but those for the brown clay are relatively high. It is generally accepted that the carbon isotopic composition of plant material is correlated with C3 and C4 pathways of carbon fixation in photosynthesis. δ13C values for C3 plants fall around -26%, while those for C4 plants -13%. C3 plants dominate areas of higher precipitation and low temperature, while C4 plants favor conditions of aridity and hot climates. Climate changescause changes in the ratio of C3 and C4 plants, which will be reflected in changing δ13C values of organic matter in sediments. The balance between C3 and C4plants depends on temperature and humidity, so the interpretation of the δ13Crecord in lake sediments is complicated. Results of this study confirmed that the peat deposits, which developed in different parts of the Caohai basin, formedduring tectonic intermittent uplift, and there is no close relationship betweencharacteristic low δ13C values of these peat deposits and climate fluctuation. δ13C profile of the core ZHJ from the Caohai basin and the δ13C record from highland peats in southern India show opposite trends in response to palaeoclimate changes. A good correlation between δ13C record and wet/arid fluctuation is observed for peats in southern India, and low δ13C values are correspondingto wetter stages of summer monsoon strengthening, when the mean temperature is higher. In the case of Caohai core, periods of higher mean temperature are corresponding to higher δ13C values. Both the two cases could be interpreted in terms of preferences of the C3 and C4 plants for different climate condition. The δ13C record of the core ZHJ from Lake Caohai shows that the summer monsoon reached maximum at the beginning of the early Holocene, then it weakened during the mid Holocene. This is in agreement with the summer monsoon circulation in Qinghai Xizang Plateau of China and southern India. It implies that Yunnan Guizhou Plateau and Qinghai Xizang Plateau of China, and southern India, locatedall in the domain of southwest monsoon, have a similar trend of palaeoclimate and palaeoenvironmental changes during late Pleistocene Holocene period.
出处
《地球化学》
CAS
CSCD
北大核心
2000年第4期390-396,共7页
Geochimica
基金
国家自然科学基金资助项目!(49773185)
关键词
湖泊沉积物
δ^13C值
古气候
草海
贵州
lacustrine sediment
δ13C
palaeoclimate
Lake Caohai
Guizhou Province
