Wavelet-based verification of a relative paleointensity record from the North Pacific

Ji Young Shin,Yongjae Yu,Wonnyon Kim

doi:10.1186/s40623-019-1067-x

Abstract

We present a relative paleointensity (RPI) record for the last ~ 1.1 Myr estimated from a sediment core in the central North Pacific, with quality verification using wavelet analysis. Rock magnetic analysis reveals that a stable remanence is carried mainly by single-domain (SD) biogenic magnetite and pseudo-SD detrital magnetite and that concentration- and grain-size-related bulk magnetic parameters vary by a factor of 3, initially meeting a conventional standard for RPI estimation. However, a further test using wavelet spectra of RPI proxies normalized by anhysteretic remanent magnetization (ARM) or isothermal remanent magnetization (IRM) shows intermittent orbital contamination at period of 100 kyr. A part of the 100-kyr orbital frequency in ARM-normalized RPI has a coherence and physical relationship with the normalizer. For the same time interval, a prominent 100-kyr cycle in the ARM/IRM wavelet spectra is also coherent with RPI, indicating that relative changes in biogenic and detrital magnetite were not well compensated by ARM normalization. For the selected RPI proxy using IRM normalization, a significant physical relationship with the lithology of magnetic minerals was not detected in the wavelet analysis, and thus, its intermittent orbital cycles could be of climatic origin, probably induced by non-magnetic factors. Nevertheless, our RPI record is consistent with global RPI stacks and provides a successful reconstruction of paleointensity with geomagnetic field origin in the North Pacific.

Highlights

Temporal variations in geomagnetic paleointensity are fundamental for understanding the geodynamo process and have been closely investigated via geological materials such as rocks and sediments (e.g., Tric et al 1992; Laj et al 2000; Channell et al 2014)
We present a high-quality relative paleointensity (RPI) record for the last ~ 1.1 Myr from the Hess Rise in the North Pacific, verified using wavelet analysis
As the demagnetizations display the stable component commonly from 10 to 40 mT, where the remanence intensities account for ~ 48–89% of the total natural remanent magnetization (NRM), a principal component analysis (PCA) method was applied to six consecutive alternating field (AF) data points of each sample to isolate the characteristic remanent magnetization (ChRM)

Summary

Introduction

Temporal variations in geomagnetic paleointensity are fundamental for understanding the geodynamo process and have been closely investigated via geological materials such as rocks and sediments (e.g., Tric et al 1992; Laj et al 2000; Channell et al 2014). Searches for orbital periods in paleointensity have been performed for high-resolution and globally stacked RPI signals such as SINT-800, SINT-2000, and PISO-1500 (e.g., Heslop 2007; Channell et al 2009), as well as deep-sea floor magnetization records and beryllium production records (e.g., Thouveny et al 2008; Saracco et al 2009). Some studies have suggested relationships between orbital signals and paleomagnetic intensity and directional changes (e.g., Fuller 2006; Thouveny et al 2008), but no statistically significant orbital periods have been detected from global RPI stack records (e.g., Heslop 2007; Channell et al 2009; Ziegler et al 2011)

Methods

Results

Discussion

Conclusion