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

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.

A full sequence of the Matuyama–Brunhes geomagnetic reversal in the Chiba composite section, Central Japan

“…On the other hand, k LF mainly reflects the total amount of magnetic minerals in a specimen, irrespective of the magnetic grain size. Therefore, the k ARM /k LF ratio is a conventional proxy for the grain size of magnetic particles in a specimen; an increase in the k ARM /k LF ratio indicates the relative contribution of finer magnetic particles and vice versa (e.g., Yamazaki 2008;Yamazaki and Ikehara 2012;Shin et al 2019).…”

“…k LF was not used as a normalizer in this study, because it may be less effective due to possible influence from diamagnetic and paramagnetic minerals and large ferrimagnetic grains that do not carry NRM (Shin et al 2019). The Pearson linear correlation coefficient (R-value ARM and R-value IRM ), associated with the slope of the NRM intensity left at certain demagnetization steps against the ARM or IRM left at the same demagnetization steps, was calculated to monitor the goodness of the slope fit (Channell et al 2002;Shin et al 2019). A comparison of the proxies used for relative paleointensity between this study and the previous studies (Okada et al 2017;Simon et al 2019) is in Figure S1.…”

Recording Fidelity of Relative Paleointensity Characteristics in the North Pacific Ocean

“…The model of Ziegler and Constable (2015) is based mainly on records from the equatorial Pacific Ocean, so their documented low-field variability over the Pacific Ocean could be biased; 10.1029/2021JB022068 Figure 9. Comparisons of core NP02 Relative paleointensity (RPI) estimates with (a) global stacks (Sint-2000Valet et al, 2005, PISO-1500Channell et al, 2009, and GLOPIS Laj et al, 2004; regional stacks from the equatorial (West Caroline Basin stack, Yamazaki et al, 2008), midlatitude (NOPAPIS-250, Yamamoto et al, 2007), and subarctic Pacific Ocean (Zhong et al, 2020); and (b) individual RPI records of core BOW-8A (Okada et al, 2005), Site 883/884 (Roberts et al, 1997;Roberts, 2008), core GC1 + PC7 (Inoue & Yamazaki, 2010;, core NGC65 (Yamazaki, 1999), and core NPGP1401-2A (Shin et al, 2019). The Laschamp excursion is denoted by the pink shaded area.…”

“…Relative paleointensity (RPI) variations of Earth's magnetic field have been used as a chronological tool in marine sediments (e.g., Channell et al, 2009;Channell, Hodell, et al, 2016;Guyodo & Valet, 1996, 1999Valet et al, 2005;Yamamoto et al, 2007). This makes RPI variations valuable in environments like the deep North Pacific Ocean (Roberts et al, 1997;Shin et al, 2019;Yamamoto et al, 2007;Yamazaki, 1999). The main advantage of the RPI approach is that dipole geomagnetic variations are recorded synchronously around the world and represent a geophysical measurement that is independent of seawater chemistry and that can be used to develop independent age constraints (Roberts et al, 2013).…”

Dating North Pacific Abyssal Sediments by Geomagnetic Paleointensity: Implications of Magnetization Carriers, Plio-Pleistocene Climate Change, and Benthic Redox Conditions

“…Since the pioneer studies of Ninkovich et al (1966), Opdyke and Foster (1970) and Kent and Lowrie (1974), reversal magnetostratigraphy has been the primary method to date North Pacific abyssal sediments. The sedimentary records of past geomagnetic polarity changes still form the backbone of most more recently published sediment chronologies from that region (Yamazaki and Ioka, 1997;Yamazaki and Oda, 2005;Korff et al, 2016;Shin et al, 2019). However, the temporal resolution of the Neogene geomagnetic polarity timescale is limited by the occurrence of only 3-5 geomagnetic polarity reversals per million years (Valet et al, 2005;Ogg, 2020).…”