Extending Global Continuous Geomagnetic Field Reconstructions on Timescales Beyond Human Civilization

Abstract

Study of the late Quaternary geomagnetic field contributes significantly to understanding the origin of millennial‐scale paleomagnetic secular variations, the structure of geomagnetic excursions, and the long‐term shielding by the geomagnetic field. A compilation of paleomagnetic sediment records and archeomagnetic and lava flow data covering the past 100 ka enables reconstruction of the global geomagnetic field on such long‐term scales. We use regularized inversion to build the first global, time‐dependent, geomagnetic field model spanning the past 100 ka, named GGF100k (Global Geomagnetic Field over the past 100 ka). Spatial parametrization of the model is in spherical harmonics and time variations with cubic splines. The model is heavily constrained by more than 100 continuous sediment records covering extended periods of time, which strongly prevail over the limited number of discrete snapshots provided by archeomagnetic and volcanic data. Following an assessment of temporal resolution in each sediment's magnetic record, we have introduced smoothing kernels into the forward modeling when assessing data misfit. This accommodates the smoothing inherent in the remanence acquisition in individual sediment paleomagnetic records, facilitating a closer fit to both high‐ and low‐resolution records in regions where some sediments have variable temporal resolutions. The model has similar spatial resolution but less temporal complexity than current Holocene geomagnetic field models. Using the new reconstruction, we discuss dipole moment variations, the time‐averaged field, and paleomagnetic secular variation activity. The new GGF100k model fills the gap in the geomagnetic power spectrum in the frequency range 100–1,000 Ma−1.

The Role of Geomagnetic Field Intensity in Late Quaternary Evolution of Humans and Large Mammals

“…A recently published RPI stack for 10‐40 ka based on high‐deposition‐rate sediments from the Iberian Margin and elsewhere (Figure ) is supported by paleointensity estimates from revised calculation of 10 Be flux in Greenland ice cores (Channell et al, ) using the GICC05 Greenland ice‐core age model (Svensson et al, ). Models and stacks covering the same 0‐ to 40‐ka interval that use RPI data from lower sedimentation rate sequences (e.g., Panovska et al, ) cannot resolve the detail that is revealed by higher sedimentation rate sequences and by 10 Be flux in ice cores.…”

One Hundred Thousand Years of Geomagnetic Field Evolution

“…Summary diagram of geomagnetic field models, paleointensity stacks, and dipole moment reconstructions covering timescales from the Holocene to 5 Ma. References: OH1992 (Ohno & Hamano, ), OH1993 (Ohno & Hamano, ), CALS10k.1b (Korte et al, ), CALS10k.2 (Constable et al, ), HFMx, HFM.OL1 (Panovska et al, ), HFM.OL1.A1 (Constable et al, ), YOS2000 (Yang et al, ), SHA.DIF.14k (Pavón‐Carrasco et al, ), MS1982 (McElhinny & Senanayake, ), GEOMAGIA VADM (Knudsen et al, ), C2018‐Overall stack (Channell et al, ), NAPIS‐75 (Laj et al, ), IMOLE (Leonhardt et al, ), LSMOD.1 (Brown et al, ), LSMOD.2 (Korte, Brown, Panovska, & Wardinski, ), GLOPIS‐75 (Laj et al, ), SAPIS (Stoner et al, ), GGF100k (Panovska, Constable, & Korte, ), sint‐200 (Guyodo & Valet, ), IMIBE (Lanci et al, ), NOPAPIS‐250 (Yamamoto et al, ), SAS‐300 (Hofmann & Fabian, ), SASC‐300 (Hofmann & Fabian, ), RADM (Ziegler & Constable, ), S1999 (Shao et al, ), IMMAB4 (Leonhardt & Fabian, ), IT2008 (Ingham & Turner, ), sint‐800 (Guyodo & Valet, ), PISO‐1500 (Channell et al, ), HINAPIS‐1500 (Xuan et al, ), M1995 (Mazaud, ), sint‐2000 (Valet et al, ), PADM2M (Ziegler et al, ), EPAPIS‐3Ma (Yamazaki & Oda, ), NARPI‐2200 (Channell et al, ), SK1990 (Schneider & Kent, ), GK1993 (Gubbins & Kelly, ), MM1977 (Merrill & McElhinny, ), LN1, LR1 (Johnson & Constable, ), MMM1996 (McElhinny et al, ), LSN1, LSR1 (Johnson & Constable, ), KG1997 (Kelly & Gubbins, ), CC1998 (Carlut & Courtillot, ), MF‐1, MF‐2, MF‐3 (Shao et al, ), LN3, LN3‐SC (Cromwell et al, ).…”

“…Roberts () discussed the strengths and limitations of u‐channels and suggested strategies for mitigating the limitations of these measurements. In field modeling, however, it is preferable to take account of the instrument convolution in the forward modeling thereby directly predicting the smoothed observations (Panovska et al, ).…”

“…Archeomagnetic/volcanic data usually have a priori uncertainties assigned and published in the original studies, in contrast to the majority of sediment studies. In all cases when uncertainties are not available, or are smaller than a certain plausible threshold, it has become customary to allocate minimum uncertainties (e.g., Korte et al, ; Panovska, Constable, & Korte, ). Other methods include introducing a modeling error and adding it in quadrature to the original data uncertainty (Licht et al, ), assigning minimum errors based on the number of samples/specimens used to calculate the mean (Nilsson et al, ), grouping the data in different categories based on paleomagnetic quality criteria (Korte et al, ; Pavón‐Carrasco et al, ), and via comparison with historical data, considering error estimates for the difference (Arneitz et al, ).…”

“…Age range of the sediment records (colored by component) used to build the GGF100k model (Panovska, Constable, & Korte, ). Record names are omitted.…”