Relative paleointensity of the geomagnetic field during Brunhes Chron recorded in North Pacific deep-sea sediment cores: orbital influence?

Relative paleointensity records of the geomagnetic field during the Brunhes Chron were obtained from two sediment cores in the North Pacific near the Hess Rise. The cores, taken below the carbonate compensation depth (CCD), showed an oxidized environment, and accompany little paleoclimatically induced lithological changes. Homogeneity of magnetic mineralogy and magnetic grain size, which are prerequisites for sedimentary paleointensity, were thoroughly examined using various techniques including low-temperature magnetometry, room-temperature hysteresis parameters, and S ratio. Isothermal remanent magnetization (IRM) was used as a normalizer of the natural remanent magnetization (NRM). The appropriateness of the normalization was checked by the absence of correlation between the normalized intensity (NRM/IRM) and the normalizer (IRM). The relative paleointensity records obtained are generally similar to the datasets from the east and central equatorial Pacific. Spectral analysis showed significant power at the orbital eccentricity (100 kyr) frequency in the relative intensity record, but not for the normalizer. This suggests orbital influence on the geomagnetic field intensity, but the possibility of paleoclimatic contamination through rock-magnetic changes should be examined further using cores from different sedimentary regime.