渤海沉积记录的末次冰期千年尺度古环境与古气候变化

Millennial-scale paleoenvironment and paleoclimate changes recorded in the Bohai Sea sediments during the last glacial period

  • 摘要: 末次冰期千年尺度古气候变化事件在全球大部分载体中均有不同程度的记录,但在海岸带—陆架区的沉积记录中该事件还未见有报道。对取自渤海的BH08孔上部26m的岩芯进行了高分辨率粒度测试与分析,结合AMS 14C测年结果和微体古生物特征,探讨了研究区末次冰期以来古环境和古气候变化。运用粒级-标准偏差法对粒度数据进行研究,发现BH08孔敏感组分(88.4~148.7μm)的变化记录了末次冰期D-O(Dansgarrd-Oeschger)旋回冷暖事件:在暖期时敏感粒级粗组分(88.4~148.7μm)的含量低,而在冷期时含量高,且可以与反映东亚夏季风的指标对应。在暖期时,强盛的夏季风带来丰富的降水,增加的径流可以将粗粒沉积物搬运至更远的下游区,且暖湿气候有利于植被的发育,使得流域内粗粒沉积物减少;而在冷期呈现相反的变化趋势。我们推测,在末次冰期低海面的背景下,格陵兰和北大西洋等高纬地区气候变化导致大气环流和/或洋流系统发生改变,从而对东亚夏季风降水的调控造成河流输入物质的变化可能是造成BH08岩芯敏感组分变化的主要原因。

     

    Abstract: The millennial-scale paleoclimatic change during the last glacial stage has been recorded in various achieves worldwide, but nothing has been heard from the sedimentary records in a coastal zone. In order to dig out the sedimentary records from the coastal region, we carried out high-resolution grain-size analysis for the upper 26m of the core BH08 collected from the Bohai Sea, together with AMS 14C dating and microfossils studies. Based upon them, the paleoenvironment and paleoclimate changes of the study area since the last glacial stage are discussed. Grain-size data is treated with the grain size and standard deviation method. It is found that the sensitive component (88.4~148.7μm) of the core BH08 sediments well recorded the D-O (Dansgarrd-Oeschger) cycle of the last glacial stage: the content of the sensitive component (88.4~148.7μm) was low in warm periods, but high in cold periods. The cyclicities of sensitive component are also corresponding to the index reflecting the East Asian summer monsoon. During the warm periods, strong summer monsoon would bring in abundant precipitation, and the increased runoff might transport the coarse-grained sediments to the distant downstream areas. In addition, warm and humid climate is conducive to the development of vegetation, resulting in the reduction of coarse-grained sediments in the drainage basin, and vise versa. It is speculated that in the last glacial stage, climate in the high latitudes such as Greenland and the North Atlantic might cause changes in atmospheric circulation and/or ocean current systems by the precipitation of the East Asian summer monsoon, and thus control the changes of the input sediments from rivers. It may be the main reason for the change of grain-size in the core BH08.

     

/

返回文章
返回