Detailed study on the anisotropy of magnetic susceptibility of arctic marine sediments

Five sediment cores from three different areas, the Jan Mayen Fracture Zone in the Greenland Sea, the Fram Strait and the Makarov Basin in the Arctic Ocean have been subjected to a detailed analysis of the magnetic fabric by analysing their anisotropy of magnetic susceptibility (AMS) as a supplementary parameter to already existing palaeo- and rock magnetic data sets. Intervals of reversed inclinations documented within the five cores can be interpreted as geomagnetic excursions because all the investigated sediments are characterized by an undisturbed magnetic fabric as expected for layered sediments, that is, an oblate anisotropy ellipsoid with its short principal axis oriented vertically. Excursional directions are also not associated with significant changes in rock magnetic parameters. However, cores from the Arctic Ocean, in particular, exhibit a strong cyclicity in their anisotropy parameters. Here, sand-rich layers are characterized by a low anisotropy, whereas clay rich layers yielded highest anisotropy degrees of up to 9 per cent indicating an AMS mainly controlled by the matrix properties of the sediment. A simple three-axis determination of the anisotropy of anhysteretic remanent magnetization (AARM) on one of these cores surprisingly yielded an even higher degree of anisotropy of the ferrimagnetic fraction of up to 18 per cent, i.e. twice as high as determined for the susceptibility, which is also influenced by the paramagnetic fraction. This implies a strong contribution of this sediment fraction to the overall magnetic susceptibility of the investigated Arctic Ocean deposits.