Age determination of sediment cores from the North Atlantic Ocean

The clay mineralogy of four 5.5- to 13.5-m-long cores sampled between 45° and 60°N in the North Atlantic Ocean has been investigated at high latitudes within a well-constrained chronostratigraphic scale. Cross-correlation spectral analyses have been performed on both clay mineral and delta18O planktonic records. Detrital clay minerals display strong signals which are coherent with the delta18O record, within the three main Milankovitch frequency bands (eccentricity, obliquity, and precession). The climatic control on clay mineral sedimentation largely depends on the latitudinal location of the sediment cores. The 100,000-year signal occurs as a uniformly acting factor, whereas the 41,000-year signal dominates clay sedimentation at high latitudes and the 23,000-year signal dominates at midlatitudes. We suggest that the latitudinal variations of the orbital forcing on the detrital clay mineral distribution in the North Atlantic Ocean not only result from climatic control of the intensity of physical and chemical weathering, but also from latitudinal control on the detrital clay supply linked to influences of the high-latitude wind-driven and midlatitude ocean-driven transportation processes, respectively.

本研究针对北大西洋北纬45°至60°区间采集的4根长度为5.5至13.5米的岩心，在高纬度区域基于严格约束的年代地层标尺开展了黏土矿物学（clay mineralogy）研究。研究人员同时对黏土矿物数据与浮游生物δ18O（delta18O）记录开展了交叉相关光谱分析（cross-correlation spectral analyses）。结果显示，陆源黏土矿物（detrital clay minerals）在偏心率（eccentricity）、黄赤交角（obliquity）与岁差（precession）这三个主要米兰科维奇频段（Milankovitch frequency bands）内，展现出与δ18O记录高度吻合的强信号。黏土矿物沉积所受的气候调控作用，在很大程度上取决于沉积岩心的纬度位置：10万年尺度的信号表现为全域统一的影响因子，而4.1万年尺度的信号在高纬度区域的黏土沉积中占据主导地位，2.3万年尺度的信号则主导中纬度区域的黏土沉积过程。本研究提出，北大西洋区域陆源黏土矿物分布所受轨道强迫（orbital forcing）的纬度差异，不仅源于物理与化学风化强度的气候调控，还分别受到高纬度风力驱动、中纬度洋流驱动的搬运过程对陆源黏土供给的纬度控制作用。