Abstract
Abstract A paleomagnetic study was conducted on a sediment core KR0310-PC1 taken from the central North Pacific in order to obtain a relative paleointensity record in the Matuyama chron from this region. The core reached to about 1.6 Ma. The age control is based on the correlation of the S ratio (S −0.1T) variations with a global oxygen-isotope stack. Isothermal remanent magnetization (IRM) was used as the normalizer of the relative paleointensity estimation; anhysteretic remanent magnetization (ARM) was not adopted because ARM is sensitive to magnetostatic interaction among magnetic particles, which is evidenced in these sediments by an inverse correlation between the ratio of ARM to saturation IRM (SIRM) and SIRM without significant magnetic grain-size changes. For the last 350 kyrs, the record of core NGC65, which was obtained at practically the same site as KR0310-PC1 and covers the Brunhes chron (Yamazaki, 1999), was incorporated because the upper part of KR0310-PC1 was physically disturbed. In the record of NGC65/KR0310-PC1, the average paleointensity in the late Matuyama chron is not lower than that during the Brunhes chron, which does not support the conclusion of Valet et al. (2005) based on their Sint-2000 stack. A spectral analysis on the NGC65/KR0310-PC1 paleointensity record shows a power at the ∼100 kyr eccentricity period. The relative paleointensity and magnetic properties of NGC65/KR0310-PC1 were compared with those of MD982185 from the western equatorial Pacific (Yamazaki and Oda, 2002, 2005). The two sites belong to different oceanographic regimes. Coherent variations in the relative paleointensity despite incoherent changes in the magnetic properties suggest that rock-magnetic contamination to the relative paleointensity is small, if any, and the ∼100 kyr period in the relative paleointensity records would reflect the geomagnetic field behavior.
Highlights
Information on the intensity of the past geomagnetic field is indispensable for understanding the mechanism of the geodynamo
We discuss more about our preference of Isothermal remanent magnetization (IRM) to anhysteretic remanent magnetization (ARM) as the normalizer
Because the difference in the variations between ARM and IRM intensities is smaller than those of natural remanent magnetization (NRM) intensity in the present core, a general pattern of the normalized intensity records such as a succession of peaks and troughs agrees between the normalization by ARM and IRM (Fig. 3(f))
Summary
Information on the intensity of the past geomagnetic field (paleointensity) is indispensable for understanding the mechanism of the geodynamo. Using this strategy, Yokoyama and Yamazaki (2000) suggested that the ∼100 kyr period would be inherent to the geomagnetic field; five relative paleointensity records from the Pacific during the Brunhes chron showed a good coincidence in this time scale despite significant phase differences in magnetic properties.
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