浙江近海海域近百年来的沉积硅藻记录及定量古环境重建

Climate change over the last century was largely impacted by human activities, and it's a key link of ancient geologic records and instrumental data, a basis for predicting climate change in future. The north of coastal area in Zhejiang is near to the Changjiang Estuary, so it's sensitive to changes in the strength of East Asian Monsoon and the flow direction of Changjiang River diluted water. The distribution of diatoms from surface sediments around the coastal area in Zhejiang will be studied in this project, with a purpose of constructing a database of diatom-environmental variables(including winter sea-surface temperature SST and summer sea-surface salinity SSS). Besides, changes in abundance of diatoms from three gravity cores along the coastal area in Zhejiang will also be analyzed in this project, and diatoms' response to oceanic environmental change over the last century will be discussed. On the basis of the diatom-environmental variables database, an approprite transfer function will be selected to reconstruct changes in SST and SSS over the last century in the study area. The final aim for this project is to reconstruct the SST/SSS along the coastal area in Zhejiang over the last century, and discuss palaeoceanic environment change and its response to East Asian Monsoon or El Ni?o-Southern Oscillation.

近百年来是人类活动对气候影响的最重要时期。近百年来的气候变化是衔接地质记录与器测资料的关键环节，也是预测未来气候变化的基础。浙江近海北部紧邻长江口，对东亚季风及其作用下长江冲淡水的季节性转向反应灵敏。本项目将分析浙江近海海域的表层沉积硅藻样品，建立该区的硅藻-环境变量数据库。并系统分析浙江近海3个高分辨率钻孔近百年来的沉积硅藻记录，探讨硅藻组合变化与古海洋环境变迁（如温度和盐度）之间的关系。在硅藻-环境变量数据库基础上，建立适合于对浙江近海钻孔硅藻数据进行古温度/古盐度计算的转换函数，其最终目标是重建浙江近海海域近百年来的古温度/古盐度变化曲线，以此为依据定量研究浙江近海近百年来的气候变化规律，讨论其与季风气候、厄尔尼诺-南方涛动以及全球变化的关系。

项目系统地对浙江近海表层沉积硅藻及浙江外海一高分辨率沉积钻孔中的硅藻面貌进行了分析，建立了反映不同气候条件下不同海洋环境的硅藻组合。我们在已有环太平洋边缘海表层沉积硅藻-环境变量数据库的基础上，在浙江近海增加了表层站位，并定量重建了浙江外海，东海西南部一钻孔中全新世以来的冬季表层海水温度和夏季表层海水盐度变化。结果表明，近千年来的冬季表层海水温度变化反映的东亚冬季风变化与北极涛动之间相关关系与北极海冰覆盖面积有关，当海冰覆盖面积减少时，冬季风与北极涛动呈显著的正相关关系，而当海冰覆盖面积增加时，冬季风与北极涛动并无明显的相关关系，即北极海冰覆盖面积的减少会导致北极涛动对冬季风的影响增强，从而进一步引起东海海洋环境的变化。中全新世以来东海夏季海水表层盐度逐渐升高的趋势与董哥洞石笋记录的中全新世以来东亚夏季风逐渐减弱的特征有很好的一致性，表明中全新世以来东海表层海水盐度的增加与东亚夏季风减弱导致的降雨量减少有关。此外，中全新世以来东海夏季海水表层盐度升高的趋势还与格陵兰冰芯记录的中全新世以来温度逐渐降低的特征以及生物标志物IP25反映的北极地区春季海冰覆盖不断增加的趋势有较强的相关性。这表明北极海冰覆盖面积的变化不仅会加强北极涛动对冬季风的影响，还与东亚夏季风降雨量变化存在一定的关联，北极春季海冰覆盖减少，对应夏季风降雨减少，东海夏季表层海水盐度升高；海冰增加，则夏季风降雨也增加，东海夏季表层海水盐度则降低。