Magnetic anisotropy and environmental changes in two sedimentary cores from the Norwegian Sea and the North Atlantic

We have studied the magnetic properties and the magnetic anisotropy (AMS and AARM) of cores MD95-2010 from the Voering Plateau and SU90-33 from the south Icelandic basin. In the first core, the study has been focussed on climatic stage 3 during which the record of magnetic susceptibility is correlated with the δ18O signal from the Greenland ice cores. Minima (maxima) in susceptibility, anhysteretic remanent magnetization and isothermal remanent magnetization coincide with cold (warm) periods and reflect a modulation in the amount of deposited magnetite. In the second core six climatic stages have been studied. The AMS and the AARM changes are tightly correlated, showing that both are related to changes in the organization of magnetite grains in the sediment. Both magnetic fabrics are oblate and the variations of the degree of anisotropy are climatically controlled with higher values during short warm events or interglacial periods compared to cold periods. Different possible mechanisms leading to the observed fabrics are discussed. It appears that, although a differential compaction might have been active, the fabrics mainly result from depositional effects, in connection with climatic changes. Although the exact mechanisms of the link between magnetic fabrics and bottom current dynamics are, as yet, open to discussion, the study of magnetic anisotropy, which reflects the sedimentary structure, may ultimately lead to a better understanding of the coupling between atmospheric temperature changes and paleocirculation pattern in the North Atlantic and Nordic Seas.