2.5Ma以来地球轨道参数变化对黄土粒度变化的线性驱动

ASTRONOMICAL FORCING OF LOESS GRAIN-SIZE RECORD OVER THE PAST 2.5 Ma

本文对2.5Ma以来宝鸡黄土剖面粒度曲线与ETP曲线做了互功率谱和凝聚函数分析,以期反映风力强度与地球轨道参数变化的关系。结果表明,2.5Ma以来粒度记录中始终存在着与地轴倾斜度、岁差呈线性响应的41000a、23000a和19000a周期;同时,在0.6—0.0MaB.P.时段存在与偏心率呈线性响应的0.1Ma周期,在2.5—1.6MaB.P.时段存在与偏心率0.4Ma呈线性响应的周期。上述结果佐证了地球轨道变化对内陆古气候变化的线性驱动作用,但该理论不能解释在约0.9—0.6MaB.P.和1.6MaB.P.前后出现的二次较大的主导气候周期转型事件。

This paper presents coherency and cross-spectral analyses between the grain-size record at Baoji and the theoretical variations in the Earth's orbital geometry. The Baoji grain-size time series, regarded as a proxy of variations in winter monsoon intensity, is generated by employing orbital tuning approach developed by SPECMAP p roject. Results obtained indicate that the obliquity (with quasi-period of 41 000a) and precession(with quasi-periods of 23 000a and 19 000 a) of the Earth can be regarded as the linear forcings of the Baoji grain-size variations over the last 2.5 Ma. In addition, the linear forcing of the eccentricity of the Earth's orbit is also recorded in the grain-size time series, as reflected by strong periods of about 0.10 Ma in the past 0.6 Ma and of about 0.4 Ma in the interval of 2.5 to 1.6 Ma B.P. The Baoji grain-size time series, therefore, has provided compelling evidence to support the Milankovitch theory of Pleistocene ice ages. However, linear response to orbital forcing can not explain two recognized dominant period shifts, one occurring at about 1.6 Ma B. P., the other between 0.9 and 0.6 Ma B.P.