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Twenty‐two sites, subjected to an IZZI‐modified Thellier‐Thellier experiment and strict selection criteria, recover a paleomagnetic axial dipole moment (PADM) of 62.2 ± 30.6 ZAm2 in Northern Israel over the Pleistocene (0.012–2.58 Ma). Pleistocene data from comparable studies from Antarctica, Iceland, and Hawaii, re‐analyzed using the same criteria and age range, show that the Northern Israeli data are on average slightly higher than those from Iceland (PADM = 53.8 ± 23 ZAm2, n = 51 sites) and even higher than the Antarctica average (PADM = 40.3 ± 17.3 ZAm2, n = 42 sites). Also, the data from the Hawaiian drill core, HSDP2, spanning the last half million years (PADM = 76.7 ± 21.3 ZAm2, n = 59 sites) are higher than those from Northern Israel. These results, when compared to Pleistocene results filtered from the PINT database (www.pintdb.org) suggest that data from the Northern hemisphere mid‐latitudes are on average higher than those from the southern hemisphere and than those from latitudes higher than 60°N. The weaker intensities found at high (northern and southern) latitudes therefore, cannot be attributed to inadequate spatiotemporal sampling of a time‐varying dipole moment or low quality data. The high fields in mid‐latitude northern hemisphere could result from long‐lived non‐axial dipole terms in the geomagnetic field with episodes of high field intensities occurring at different times in different longitudes. This hypothesis is supported by an asymmetry predicted from the Holocene, 100 kyr, and 5 million year time‐averaged geomagnetic field models. Plain Language Summary According to the Geocentric Axial Dipole hypothesis, the geomagnetic field may be approximated by a dipole that is aligned with the spin axis and positioned in the center of Earth. Such a field would produce field strengths that vary with respect to latitude with high latitudes associated with high intensities, or, converted to equivalent “virtual” dipole moments, would be essentially independent of latitude. It has long been suggested that high latitudes have had lower field strengths than predicted by such a model, when compared to data from mid‐latitudes, but these claims have always been accompanied by caveats regarding differences in temporal coverage or methodological approaches. Here, we present new data from Pleistocene aged rapidly cooled cinder cones and lava flow tops from Israel. We compare these data to other recent data sets obtained from rapidly cooled materials collected in Hawaii, Iceland, and Antarctica. These confirm that virtual dipole moments from mid northern hemisphere latitudes are higher than those from high latitudes and from the southern hemisphere. Global compilations spanning the Pleistocene, when filtered for quality also shows this behavior as do time averaged field models. Therefore, field strengths over even millions of years can have persistent non‐dipole field contributions. Key Points We present 26 40Ar/39Ar ages from volcanic rocks from Northern Israel (90 ka to 3.3 Ma) Twenty‐two Pleistocene intensity estimates have a mean paleomagnetic dipole moment of 62.2 ± 30.6 ZAm2 The northern hemisphere had persistently higher fields than the southern during the Pleistocene

Paleointensity records are vital for understanding the Earth's evolution, but obtaining accurate paleointensity is a challenging task. The Shaw‐type method, a widely‐used paleointensity protocol, produces biased results occasionally despite strict selection criteria. By examining the relationships between paleointensities and rock magnetic parameters from a pseudo‐Tsunakawa‐Shaw experiment, we ascertain that changes in the ratio of thermal to anhysteretic remanent magnetization (R) are proportional to bias in paleointensity, especially prominent in samples with hundred‐nanometer‐scale magnetic grains, and thus proved to be the culprit for the bias. Furthermore, we develop a method exploiting the Linear regression of R with Diverse cut‐off coercivity intervals for estimating Shaw‐type paleointensities (LoRD‐Shaw). Combined with a curve fit technique for samples with “folding\" phenomenon, the LoRD‐Shaw method yields high‐accuracy results in all tested samples, demonstrating its efficiency in mitigating paleointensity bias from thermal alteration. The new method will enhance acquisition of high‐precision paleointensities for constraining the geodynamo evolution. Plain Language Summary Precise retrieval of ancient geomagnetic field strength is instrumental in elucidating the evolutionary history of the Earth's interior. Nevertheless, various paleointensity protocols including the widely used Shaw‐type method are struggling to get enough authentic data to satisfy the demand for clarifying crucial questions such as the solidification time of the Earth's inner core and interactions between different geospheres. Here, we figure out the culprit of biased results derived from Shaw‐series protocols and propose a new calculation method (LoRD‐Shaw) to solve the problem. The LoRD‐Shaw method achieves accurate results in both laboratory‐tested and modern volcanic samples with a high success rate, which will promote the acquisition of abundant high‐precision paleointensities for geomagnetic study, and thus contribute to the geoscience community. Key Points Changes in the ratio of thermal remanent magnetization to anhysteretic remanent magnetization (R) lead to bias in the Shaw‐type method Samples with magnetic grains of hundreds of nanometers are more susceptible to the R changes during thermal treatment The LoRD‐Shaw method is developed to derive accurate paleointensity results from samples even with large thermal alteration

In this study we focus on the investigation of the absolute intensity records of two volcanic subsequences, aiming to enrich the global paleointensity database for the last 5 Ma, which currently shows important dispersion. We present new absolute paleointensities obtained from the Plio‐Pleistocene volcanic sequence of Korkhi (Djavakheti Highland, Georgia) (41°27′31″N, 43°27′55″E). Korkhi is divided into two lava flow subsequences dated at 3.11 ± 0.20 Ma and 1.85 ± 0.08 Ma. Paleomagnetic directions previously published (Sánchez‐Moreno et al., 2018, https://doi.org/10.1029/2017GC007358) show a normal polarity in the lower Korkhi subsequence and a reverse‐to‐intermediate polarity in the upper Korkhi subsequence. The new paleointensity determinations are obtained through two different Thellier‐type protocols (Thellier‐Thellier and IZZI) and the corrected multispecimen method. We utilize different selection criteria and interpretation approaches (TTB, CCRIT, BiCEP and multimethod), and we make a critical evaluation on their application on complex magnetic behaviors, such as often found in volcanic rocks. Finally, we obtained a paleointensity of 70 μT in upper Korkhi and 14 paleointensities in lower Korkhi that vary between 5.2 and 37.2 μT. These results agree with a recently proposed non‐Geocentric Axial Dipole (GAD) hypothesis for the last ∼1.5 Ma (Cych et al., 2023, https://doi.org/10.1029/2023JB026492), and with low field strength for the 3–4 Ma. Plain Language Summary The Earth's magnetic field undergoes variations in both time and space. Secular variation is the continuous change in direction and intensity of the Earth's magnetic field over decades to centuries, while polarity reversals and geomagnetic excursions are long term changes, over millennia to millions of years. The nature and causes of both short‐ and long term variations are still not well known. Obtaining good quality data from the direction and intensity of the ancient magnetic field recorded in rocks allows us to reconstruct past geomagnetic variations and thus better understand the past geomagnetic field's behavior and patterns. Absolute paleointensity determinations require laborious, time‐consuming and low success rate experiments with a variety of different protocols and selection criteria. In this work, we apply different paleointensity protocols, quality selection criteria and interpretation approaches to obtain new paleointensity results from the Korkhi volcanic sequence (Georgia), which is divided into two subsequences dated at 1.85 and 3.11 Ma respectively. The main goals of the study are to obtain new paleointensity data of validated reliability to understand the behavior of the Earth's magnetic field during the last 5 Ma and to compare different protocols and selection criteria broadly used in absolute paleointensity studies. Key Points New paleointensities from Plio‐Pleistocene lava flow sequence from Georgia Determination of paleointensity with Thellier‐type protocols under RCRIT selection criteria, BiCEP methodology and multimethod approach Variable behavior of the geomagnetic field for the last 5 Ma

Determining the age of the geomagnetic field is of paramount importance for understanding the evolution of the planet because the field shields the atmosphere from erosion by the solar wind. The absence or presence of the geomagnetic field also provides a unique gauge of early core conditions. Evidence for a geomagnetic field 4.2 billion-year (Gy) old, just a few hundred million years after the lunar-forming giant impact, has come from paleomagnetic analyses of zircons of the Jack Hills (Western Australia). Herein, we provide new paleomagnetic and electron microscope analyses that attest to the presence of a primary magnetic remanence carried by magnetite in these zircons and new geochemical data indicating that select Hadean zircons have escaped magnetic resetting since their formation. New paleointensity and Pb-Pb radiometric age data from additional zircons meeting robust selection criteria provide further evidence for the fidelity of the magnetic record and suggest a period of high geomagnetic field strength at 4.1 to 4.0 billion years ago (Ga) that may represent efficient convection related to chemical precipitation in Earth’s Hadean liquid iron core.

The West Pacific Anomaly (WPA), a low geomagnetic field anomaly observed in the 16th to 18th centuries, represents a recently recognized and complex feature of Earth's magnetic field. However, the history of the WPA is still uncertain due to a scarcity of paleointensity data in Southeast Asia. Here, we conducted archeointensity analyses on pottery shards from the Xiajiaoshan site in southern China, dated to 4107 ± 123 BCE. Using Thellier–Coe and Repeated Thellier‐Series Experiment methods, we obtained high‐fidelity paleointensities ranging from 14.1 to 26.4 μT (20.7 ± 4.4 μT). These values are significantly lower than surrounding archeointensity data. We incorporated this new data into ArchKalmag14k paleomagnetic field model, which shows the presence of a geomagnetic field low‐intensity anomaly in Southeast Asia around 6,000 years ago. Our study provides the first absolute paleointensity data for low‐latitude East Asia at that time, suggesting that the WPA may have recurred approximately 6,000 years ago. Plain Language Summary The possible existence of a geomagnetic field low‐intensity anomaly in the West Pacific region has been suggested based on the observation of polar lights recorded in Korean historical texts. However, this hypothesis remains controversial due to the lack of paleointensity data. In this study, we performed detailed paleointensity analyses on pottery shards unearthed from the Xiaojiaoshan site in southern China, dating back approximately 6,000 years. Our new paleointensity results, ranging from 14.1 to 26.4 μT (20.7 ± 4.4 μT), are substantially lower compared to the present‐day intensity of 45.8 μT at the study site. These results are also significantly lower than the paleointensity data from surrounding areas in the archeointensity database. By combining our findings with other global archeomagnetic data, we updated the paleomagnetic model ArchKalmag14k. The updated model clearly shows a low‐intensity feature in the West Pacific region around 6,000 years ago. This finding provides new constraints on archeomagnetic reference curves and regional geomagnetic models in East Asia, and likely indicates the presence of a geomagnetic field anomaly. Key Points Pottery shards from southern China, dated to 6,000 years ago, recorded paleointensity values ranging from 14.1 to 26.4 μT (20.7 ± 4.4 μT) These low paleointensities suggest an anomalous geomagnetic field behavior The findings indicate the West Pacific Anomaly likely recurred in Southeast Asia 6,000 years ago

Describing the evolution of the neo-volcanic zone in the spreading ridge is essential for understanding the dynamics and environments of abyssal basins. However, the absolute dating of ocean floor basalts is generally difficult. As a characteristic age indicator, absolute intensity of past geomagnetic field (absolute paleointensity, API) is useful to date ocean floor basalts. In this study, we adopted the Tsunakawa–Shaw method to measure APIs of whole-rock seafloor basalts collected from a conical cone on the Central Indian Ridge and performed rock magnetic experiments. We conducted the experiments on a total of 18 specimens (two or three specimens from each of eight lava sites). Six specimens from two lava sites with different morphologies (pillow and sheet), three for each, passed the acceptance criteria. API means at site level are 33.0 ± 1.0 and 35.8 ± 1.7 μT, respectively. The similarity of API site means suggests that they erupted within a short period. These site-level API means are approximately 0.7 to 0.8 times the present geomagnetic intensity of 46.0 μT at the sampling sites. The accepted specimens show higher Curie temperature, lower initial intensity of natural remanent magnetization, higher ratio of saturation remanence to saturation magnetization (M rs /M s ), and signal of harder magnetic mineral than rejected ones. Our primary comparison between the two site-level API means and the 1590–present high-resolution IGRF-13 + gufm1 model constrains that the eruption timing of the conical cone to be < 1590 CE. When we compared the two site-level API means with the paleointensity curves calculated from the BIGMUDI4k.1 and ArchKalmag14 k.r, we found that they overlap in the period of − 7575 to −1675 CE or − 25 to 1590 CE, which may be the eruption timing of the conical cone. We concluded that timing of recent volcanic eruption in abyssal environment could be investigated by using appropriate rock magnetic selection and carefully examined API. Graphical Abstract

Marine sediments contain magnetic mineral particles of detrital, biogenic and authigenic origin that record changes in the direction and intensity of the geomagnetic field over geological time. Previous studies have demonstrated that the recording efficiencies of detrital and biogenic magnetite differ. Varying mixing proportions of these two primary magnetic carriers and the gradual collapse of magnetofossil chains through time should therefore modify and bias the relative paleointensity (RPI) signal. To investigate both effects, we conducted laboratory sedimentation experiments using synthetic magnetite powder of vortex to multidomain state as a detrital magnetization carrier, and extracted magnetosome crystals from Magnetospirillum gryphiswaldense MSR‐1—with and without previous ultrasonic treatment—as a biogenic magnetization carrier. Both magnetite types were suspended in kaolin‐water slurries and deposited in magnetic fields of 50 and 70 μT. RPI values derived from depositional (DRM), anhysteretic (ARM) and isothermal (IRM) remanent magnetization showed that the magnetic recording efficiencies of ordered and disordered magnetofossil were 1.7–5.3 times lower in comparison to ground synthetic magnetite. These experiments show the lower DRM acquisition efficiency of biogenic in relation to detrital magnetite. Our study sheds new light on the contrasting sedimentary magnetic recording efficiencies of detrital and biogenic magnetite, which may imply environmental bias in geomagnetic field intensity reconstructions.

Obtaining accurate estimates of the absolute intensity of the past geomagnetic field (paleointensity) is one of the major challenges in paleomagnetic research. Paleointensity data are typically determined by replacing the ancient thermoremanent magnetization (TRM) acquired in an unknown field with a laboratory TRM acquired under controlled conditions. A major source of uncertainty in paleointensity experiments arises from cooling rate effects, as the two TRMs are acquired under significantly different cooling conditions. Néel theory for single‐domain (SD) particles predicts that ancient (slow‐cooled) TRM is larger than laboratory (fast‐cooled) TRM, and that the ratio between them is linearly proportional to the logarithm of the cooling rate ratios. Here, this relationship is tested for non‐ideal SD materials, providing an empirical basis for the validity of cooling‐rate correction experiments. Eighty‐two archeological baked‐clay artifacts and basalt samples were given eight TRMs under an exponential cooling process, using seven different cooling‐rate constants spanning 2.5 orders of magnitude, resulting in cooling times ranging from 30 min to 1 week. These samples exhibited a range of domain state properties, including SD, vortex, strongly interacting particles, and mixtures of different populations. The results show that the ratio of slow‐to fast‐cooled TRMs is a linear function of the logarithm of the exponential cooling rate constants, regardless of the domain state. Cooling rate corrections, calculated for more than 2,100 archeological specimens using three different exponential cooling constants, are analyzed and provide practical guidelines for TRM effects in typical archeological materials. The results highlight that cooling rate correction should always be measured.

Natural volcanic glasses are well represented in the geologic record, and typically contain near‐ideal single‐domain particles required for standard Thellier‐type absolute paleointensity experiments. Young (<∼50–100 ka) glasses have been demonstrated to reliably record Earth's magnetic field. However, it is unclear how the magnetic mineralogy and magnetization might change with age as the metastable glass structure relaxes. Here, we attempt to systematically address issues surrounding glass relaxation and devitrification. We subjected a set of natural basaltic and rhyolitic glasses to controlled annealing experiments at temperatures between 200°C and 400°C and assessed how the magnetic properties and glass structure (as assessed by the glass transition temperature, Tg) change over time. We compare the results to bulk magnetic properties and Tg for a suite of volcanic glasses spanning over seven orders of magnitude in age. Annealed samples show an increase in isothermal remanent magnetization acquisition, a decrease in coercivity, and basaltic samples show an increase in unblocking temperatures. The results are consistent with a coarsening of pre‐existing magnetic particles rather than precipitation of new oxides. The natural data are more difficult to interpret, but trends in average parameters are consistent with a coarsening of magnetic particles in some—but not all—samples with age, and this appears to be accompanied by a reduction in Tg. While the annealing experiments take place under many different thermodynamic conditions compared to naturally aged samples, we suggest caution when using geologically older glasses for paleointensity analyses.

Paleomagnetic studies typically assume that the long‐term, time‐averaged geomagnetic field behaves as a geocentric axial dipole (GAD). While paleodirectional data over the past five million years generally agree with GAD predictions, mid‐to‐low latitude paleointensity records fail to show GAD, with high values from Hawaii. Possible causes include experimental biases, non‐dipole field contributions, and uneven temporal sampling. In this study, we conduct alternating field and thermal demagnetization measurements, as well as paleointensity experiments, on 12 late Pleistocene (∼0.2–0.5 Ma) lava flows from northern Hainan Island (∼20°N, ∼110°E) of the Brunhes normal polarity chron. Eleven sites yield stable paleomagnetic directions (D = 9.1°, I = 24.3°, α95 = 4.0°), defining a virtual geomagnetic pole (VGP) at 78.7°N, 237.7°E, with VGP dispersion of 12.9°. Paleointensity results from four qualified sites range from 28.8 to 48.9 μT (mean = 37.8 ± 6.9 μT), which are in agreement with the Brunhes Hawaiian data from the same latitude. The directional and intensity results from Hainan are consistent with previous studies at similar latitudes but deviate from GAD predictions. Our results suggest that the high paleointensity values observed in the Hawaiian region may result from differences in age distributions compared with records from other latitudes. Considering these temporal differences, the observed non‐GAD characteristics at mid‐to‐low latitudes may partly reflect comparisons between time‐averaged field properties over distinct geological intervals.