Paleomagnetic inclination variations during the last 200 kyr in the Okhotsk Sea and their relation to persistent non-axial-dipole field

Toshitsugu Yamazaki,Takaya Shimono,Seiko Inoue

doi:10.1186/s40623-016-0561-7

Abstract

Studies on geomagnetic paleointensity using marine sediments revealed that intensity fluctuations contain variations with timescales of 104 years and longer. In contrast, directional secular variations of such timescales were far less studied. In this paper we study inclination variations of longer than a millennial timescale using sediment cores at nine sites in the Okhotsk Sea. Relative paleointensity and magnetic susceptibility variations were used for inter-core correlations and age estimations. The average inclinations of individual cores were close to those of the geocentric axial dipole (GAD) field at the site latitudes. A stacked inclination curve for the last 200 kyr showed intervals of shallower inclinations at about 25–45, 75–90, 110–135, and 185–200 ka. These are synchronous with inclination shifts toward negative previously reported in the western equatorial Pacific, and temporally coincide with paleointensity lows in general. Both the Okhotsk Sea and western equatorial Pacific are within a region of outward directed flux in the persistent non-axial-dipole (NAD) field, and the synchronous inclination shifts may have been caused by a larger contribution of the NAD field when the GAD was weaker.

Highlights

Continuous records of past geomagnetic intensity variations during the last few million years recovered from marine sediments revealed that paleointensity fluctuations between polarity reversals contain variations with timescales of 104 years and longer (e.g., Guyodo and Valet 1999; Yamazaki and Oda 2005; Valet et al 2005; Channell et al 2009; Tauxe and Yamazaki 2015)
We show that synchronous inclination shifts occur in the Okhotsk Sea and western equatorial Pacific and that the inclination variations may correlate with paleointensity
Inclination records of the three major sites are shown in Fig. 3, which suggests that variations of a timescale of a few tens of 1000 years occur in common

Summary

Introduction

Continuous records of past geomagnetic intensity variations during the last few million years recovered from marine sediments revealed that paleointensity fluctuations between polarity reversals contain variations with timescales of 104 years and longer (e.g., Guyodo and Valet 1999; Yamazaki and Oda 2005; Valet et al 2005; Channell et al 2009; Tauxe and Yamazaki 2015). Occurrence of inclination variations with timescales of 104 years and longer was previously reported using sediment cores from the western equatorial Pacific (Yamazaki and Ioka 1994; Yamazaki and Oda 2002; Yamazaki et al 2008).

Results

Conclusion