Normalized Remanence in Sediments from Offshore Wilkes Land, East Antarctica

Abstract

In order to investigate the long-term changes of the geomagnetic field intensity in the Antarctic region, paleomagnetic and rock-magnetic studies have been conducted on a deep-sea sediment core obtained from offshore Wilkes Land, East Antarctica. The core covers the last about 1.1 Ma. Stepwise alternating-field (AF) demagnetization of natural remanent magnetization (NRM) revealed that a great majority of samples are characterized by a single stable component of magnetization, sometimes associated with a secondary component completely demagnetized by a 30 mT AF field. Downcore changes of magnetic concentration represented by magnetic susceptibility (χ) and anhysteretic remanent magnetization (ARM) are a factor of five or less. Variations in magnetic grain size and coercivity are estimated to be small from ratio of ARM to χ and median destructive fields of ARM respectively. These results demonstrate that the core is rock-magnetically homogeneous, and thus could be considered to yield relative paleointensity record. The ratio of the NRM demagnetized at 30 mT (NRM30mT) versus the ARM demagnetized at 30 mT (ARM30mT), which is the reasonable parameter to eliminate the effects of the secondary remanence, is interpreted as our best approximation for paleointensity estimation. Absence of correlation between the normalized intensity (NRM30mT/ARM30mT) and the normalizer (ARM30mT) shows the appropriateness of the normalization. The obtained record is similar in general to other worldwide marine records. Such a global synchronicity might be attributed to dipole intensity changes.