Magnetic Variations and Possible Milankovitch Cycles in a Deep-Sea Core from the Central North Atlantic

Magnetic measurements on 265 samples from an 8 m long deep-sea sediment gravity core, 450 km SW of Dakar, West Africa, are presented. The core is normally magnetized, thus being of Brunhes age (younger than 730 ka). Cyclic variations in the NRM intensity, the susceptibility, and especially 10 major and 20 minor cycles in the Q-ratio (Koenigsberger ratio) are discussed in relation to climatic variations. The possible effects of secondary magnetizations are not known, but because of the regular pattern in the Q-ratio, it is suggested that the periodicities in this ratio correspond to Milankovitch cycles with periods of 21 ka and 41 ka years, and therefore that the Q-ratio may be used as an easily-obtained time scale, and hence as a stratigraphical tool, in these kinds of deep-sea sediments.