Reliability of relative palaeointensities of a sediment core with climatically-triggered strong magnetisation changes

Abstract

A late Pleistocene deep-sea core was taken in the Central Atlantic near the coast of Mauritania. Large variations of magnetic properties such as natural and anhysteretic remanent magnetisation (NRM, ARM) and low field susceptibility ( k) as well as their ratios, NRM/ k and ARM/ k, coincide with oxygen isotope ratio changes. Warm periods mainly correspond to high magnetisations and cold periods to low ones. These variations are mainly due to concentration changes of fine-grained magnetite and less to changes of chemistry and grain size of ferromagnetic minerals. Therefore, ARM is preferred as a normalisation parameter for NRM. The NRM/ARM ratio reflects to a much lesser degree climatic and mineralogical changes. Previous investigations established quality criteria and limits of the variations of ferromagnetic minerals and related magnetic properties for reliable relative palaeointensity measurements. These limits are largely exceeded in the present study. However, the ages of most prominent NRM/ARM ratio lows and highs are in agreement with published relative palaeointensity data. Therefore, it is concluded that the general trend of the Earth’s magnetic field intensity changes can be preserved even in a sediment core with strong ferromagnetic mineral variations.