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Geomagnetic polarity timescale from marine magnetic anomalies for 0–160 Ma, after Lowrie and Kent (2004); largely based on Cande and Kent (1995) and Channell et al. (1995). Filled and open blocks represent intervals of normal and reverse geomagnetic field polarity. Those intervals, known as “chrons”, are labelled in an elaborate way to account for the fact that shorter chrons (subchrons) and possible but not firmly identified even shorter chrons (cryptochrons) have progressively been included (for details see e.g. Gee and Kent 2007). Only key chrons that were used as calibration tiepoints are identified by their names above the bar graph (C1n, C3n, etc.). Correlated positions of geologic period boundaries are otherwise indicated by ticks below the bar graph (N/P, Neogene/Paleogene; P/K, Paleogene/Cretaceous, K/J, Cretaceous/Jurassic). KQZ is the Cretaceous Quiet Zone, an unusually long chron also known as the Cretaceous Normal Superchron. JQZ is the Jurassic Quiet Zone, corresponding to times with low field strength (see Sect. 4.3.2)

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The magnetic field of the Earth is by far the best documented magnetic field of all known planets. Considerable progress has been made in our understanding of its characteristics and properties, thanks to the convergence of many different approaches and to the remarkable fact that surface rocks have quietly recorded much of its history. The usefuln...

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... sedimentary records, and ra- diometrically dated igneous rocks, both of which obviously also have the ability to pro- vide direct evidence of geomagnetic reversals. Combining all this information, the calibra- tion of sea-floor spreading to absolute age makes it possible to provide a reliable record of reversals for the past 160 My (see Fig. 13 and Gee and Kent 2007 for a recent de- tailed review). Most sea-floor magnetic anomalies from earlier times have unfortunately been subducted along with the oceanic crust so that longer term data only comes to us in a piecemeal fashion from the available geological record. Nevertheless, there are records of the reversal history quite ...
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... than the dominant time-scales of the secular variation (see Fig. 19). Each data must then be seen as a sample of the core field value at a given known location and at a roughly known time. Fortunately this time is often known with enough accuracy that the data belonging to a common chron in the geomagnetic polarity times scale (GPTS, recall Fig. 13) can still be used for some statistical analysis of the field at times of stable polarity. Of course, not all data correspond to such stable polarity periods and some will correspond to times of transitional (reversals) or unstable polarity (excursions). Fortunately these times can be identified and the behavior of the field during such ...
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... for very long time scale changes in geomagnetic field behavior is primarily pro- vided by three different types of paleomagnetic observations: the sequence of reversals as provided by the GPTS over the past 160 My (recall Fig. 13) and by additional more ancient, but more sparse magnetostratigraphic sequences (see e.g. Gallet 2005, 2010); a collection of paleointensity measurements (see e.g. ), a few of which date back to 3.2 Ga (e.g. Tarduno et al. 2007); and PSV estimates (up to 2.8 Gy ago, see e.g. Smirnov and Tarduno 2004;Biggin et al. 2008a). As noted in ...
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... rate is known to have slowly decreased over geological times (see e.g. Varga et al. 1998). Since all of those changes affect parameters that are important in defining planetary dynamo behavior (see e.g. Christensen and Wicht 2007), it is inevitable that they must have produced some signature in the paleomagnetic data. Both the GPTS (re- call Fig. 13) and the temporal power spectrum shown in Fig. 27, reveal long-term changes in the field behavior over periods of time commensurate with mantle convection timescales ( Schubert et al. ...
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... conditions imposed at the core surface ( ). However, an alternative interpretation of the observed tran- sition to the superchron can also be proposed, based on the more recent reversal rate estimate proposed by Hulot and Gallet (2003) for the Upper Jurassic to Lower Cretaceous time period (Fig. 28 (right), consistent with the GPTS shown in Fig. 13). As can be seen, this revised estimate no longer shows any unambiguous sign of decrease before the superchron. A care- ful look at the GPTS itself (Fig. 13) shows that the transition to the superchron may well have been very sudden. This suggests an alternative interpretation that the geodynamo could have entered the superchron as a ...
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... based on the more recent reversal rate estimate proposed by Hulot and Gallet (2003) for the Upper Jurassic to Lower Cretaceous time period (Fig. 28 (right), consistent with the GPTS shown in Fig. 13). As can be seen, this revised estimate no longer shows any unambiguous sign of decrease before the superchron. A care- ful look at the GPTS itself (Fig. 13) shows that the transition to the superchron may well have been very sudden. This suggests an alternative interpretation that the geodynamo could have entered the superchron as a result of a sudden change in its boundary conditions (for example, following the rapid arrival of a cold subducted slab at the core surface, the most effective ...
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... the case can also be found in marine magnetic anomaly profiles which happen to be particularly weak during the 167-155 Ma time period (e.g., Tivey et al. 2006;Tominaga et al. 2008). This portion of the magnetic anomaly record, found in the Pacific, displays many small amplitude fluctuations and is known as the Pacific Jurassic Quiet Zone (JQZ in Fig. 13). However, this is also an epoch for which magnetostratigraphic evidence for polarity reversals is ambiguous (as re- flected by the grey area in the GTPS of Fig. 13, also reproduced below the intensity plot in Fig. 31), and it is still unclear whether the observed anomalies truly reflect fluctuations of a weak field with few reversals, ...
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... et al. 2008). This portion of the magnetic anomaly record, found in the Pacific, displays many small amplitude fluctuations and is known as the Pacific Jurassic Quiet Zone (JQZ in Fig. 13). However, this is also an epoch for which magnetostratigraphic evidence for polarity reversals is ambiguous (as re- flected by the grey area in the GTPS of Fig. 13, also reproduced below the intensity plot in Fig. 31), and it is still unclear whether the observed anomalies truly reflect fluctuations of a weak field with few reversals, or a rapid succession of reversals ( Tivey et al. 2006;Tominaga et al. ...

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... Solar magnetic reversals show the striking feature of being periodic, in contrast to some other late-type stars like M dwarfs and T Tauri stars (age 100 Myr), whose magnetic activity shows more erratic behavior (Stauffer et al. 2017). Also, geomagnetic reversals seem to result from a chaotic (or stochastic) process (e.g., Ryan & Sarson 2008;Hulot et al. 2010;Raphaldini et al. 2021). ...
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Low-mass M dwarf stars, T Tauri stars, as well as planets such as the Earth and Jupiter are permeated by large-scale magnetic fields generated by the convection-driven dynamo operating in their convection zones. These magnetic fields are often characterized by a significant time variability, most prominently expressed by the inversions of their polarity, denoted as reversals, whose mechanism has not been completely understood. This work aims to gain some insights into the mechanism that generates these reversals. With this purpose, a simplified nonlinear model is developed to investigate the role played in polarity reversals by the convective heat transfer occurring in stellar and planetary convection zones. A model result is the enhancement of the global heat transport before polarity reversals, showing the crucial role that heat transport might play in their occurrence. This role is elucidated by considering that a reversal has a greater than 70% probability of occurring during a burst of convective heat transport. This high probability has been found in 94 out of 101 numerical simulations obtained by changing characteristic model parameters. Moreover, the causal relationship between the convective heat flux growth and the magnetic field variations is highlighted by the temporal antecedence of the former relative to the latter and by convergent cross mapping, namely a statistical test for detecting causality. It would thus be expected that higher levels of temporal variability in the planetary and stellar magnetic fields may be correlated to a higher heat transfer efficiency achieved in the interior of these celestial bodies.
... Geological records from volcanic rocks are considered highly appropriate for determining the statistical properties of paleofield behaviour over the past few million years. These materials offer instantaneous readings of the paleomagnetic field in contrast to the smoothed recording in sedimentary rocks (Hulot et al., 2010). Over the past 14 years, global compilations of high-quality paleomagnetic data (from lava flows and thin dykes) have been produced for the last 5 Myr (Johnson et al., 2008;Opdyke et al., 2015) and 10 Myr (Cromwell et al., 2018) to constrain PSV and TAF models. ...
Article
Improvements in the spatial and temporal coverage of paleomagnetic data are essential to better evaluate paleofield behaviour over the past 10 Myr, especially due to data scarcity at low latitudes in the South American region. Here, we provide new Pleistocene-Holocene (0–2 Ma age interval) paleodirectional data from three volcanic systems (Doña Juana Volcanic Complex, Galeras Volcanic Complex and Morasurco Volcano) in southwestern Colombia between latitudes 1.2 and 1.4°N. A total of 38 paleodirectional sites were studied using progressive alternating field and thermal demagnetization treatments. After excluding transitional data, we obtain thirty site-mean directions for analysis of paleosecular variation (PSV) and the time-averaged field (TAF) in the study area. The mean direction (Dec = 351.2°, Inc. = −3.4°, α95 = 6.2°, k = 20.0) and the paleomagnetic pole (Plat = 80.7°N, Plon = 173.1°E, A95 = 5.2°, K = 29.1) of these sites are not statistically compatible with the expected geocentric axial dipole (GAD) field direction and geographic north pole, respectively. Virtual geomagnetic pole dispersion (SB) for our filtered dataset (SB(2Ma) = 15.2(12.0; 17.6)°) and the Brunhes chron (SB(Bru) = 16.0(11.6; 19.1)°) are consistent at the 95% confidence level with South American studies at equatorial latitudes and recent PSV models for the 0–10 Ma and Brunhes intervals. Likewise, the corresponding inclination anomaly (ΔI) for two age groups ΔI2Ma = − 5.9(−12.1; 0.3)° and ΔIBru = − 5.3(−13.7;3.1)° suggests large deviations relative to the GAD model, in accordance with predictions from zonal TAF models. The high VGP dispersion could be linked to strong longitudinal variability of the magnetic equator position over South America. This feature reflects the presence of significant non-dipole field components in this region that have been detected in geomagnetic field models for the most recent centuries and millennia, probably associated with the presence of the South Atlantic Magnetic Anomaly in the South American region.
... At a given marine energy site, it is essential to understand what signals marine organisms are encountering from natural magnetic fields before drawing any conclusions about the potential impact of a cable. This is complicated by the fact that while Earth's magnetic field intensity remains stable over the long term, intensity, inclination, and declination can vary spatially and temporally with no apparent pattern at any specific location [20]. Geomagnetic declination is better documented than intensity; in our study region of the Pacific Northwest, it is currently decreasing at a rate of 0.1 degree per year, and it is possible that the background intensity could change year to year. ...
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Unknowns around the environmental effects of marine renewable energy have slowed the deployment of this emerging technology worldwide. Established testing methods are necessary to safely permit and develop marine energy devices. Magnetic fields are one potential cause of environmental effects and are created when electricity is generated and transmitted to shore. Further, the existing variation of the background magnetic field at sites that may be developed for marine energy is largely unknown, making it difficult to assess how much additional stress or impact the anthropogenic magnetic field may have. This study investigates two instruments for their ability to characterize the background magnetic fields at a potential marine energy site in Sequim Bay, WA. Based on this evaluation, this study recommends an Overhauser magnetomer for assessing the background magnetic field and demonstrates the use of this sensor at a potential marine energy site.
... Magnetic fields are ubiquitous in the universe. They are observed at a wide range of spatial scales and field strengths; the average magnetic field strength on the surface of Earth is about 0.5 G (Hulot et al. 2010;Guyodo & Valet 1999) and on the Sun about 1 G (Scherrer et al. 1977), while it can reach several thousand Gauss in sun spots (e.g. Jurčák et al. 2018;Schmassmann et al. 2018). ...
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We analyse observational signatures of magnetic fields for simulations of a Milky-Way like disc with supernova-driven interstellar turbulence and self-consistent chemical processes. In particular, we post-process two simulations data sets of the SILCC Project for two initial amplitudes of the magnetic field, $B_0 =$ 3 and 6 $\mu$G, to study the evolution of Faraday rotation measures (RM) and synchrotron luminosity. For calculating the RM, three different models of the electron density $n_e$ are considered. A constant electron density, and two estimations based on the density of ionized species and the fraction of the total gas, respectively. Our results show that the RM profiles are extremely sensitive to the $n_e$ models, which assesses the importance of accurate electron distribution observations/estimations for the magnetic fields to be probed using Faraday RMs. As a second observable of the magnetic field, we estimate the synchrotron luminosity in the simulations using a semi-analytical cosmic ray model. We find that the synchrotron luminosity decreases over time, which is connected to the decay of magnetic energy in the simulations. The ratios between the magnetic, the cosmic ray, and the thermal energy density indicate that the assumption of equipartition does not hold for most regions of the ISM. In particular, for the ratio of the cosmic ray to the magnetic energy the assumption of equipatition could lead to a wrong interpretation of the observed synchrotron emission.
... Geomagnetic data are obtained by measuring the total vector B of the geomagnetic field and its three orthogonal components at different points on the Earth. Observations are carried out by the groundbased magnetometers installed at the full-fledged magnetic observatories and magnetic stations and by the space-based magnetic instruments onboard low Earth-orbiting satellites (Hulot et al., 2010). An additional source of the geomagnetic data is the measurements of the lithospheric magnetic field. ...
... An additional source of the geomagnetic data is the measurements of the lithospheric magnetic field. On the scales from 250 to 3000 km, the lithospheric field can be mapped globally based on the data from low orbiting satellites (Hulot et al., 2010). On the scales shorter than 250 km, the lithospheric field becomes too small to be detected at the height of satellite orbits. ...
... A full-fledged ground-based geomagnetic observatory records the total vector of the geomagnetic field strength and variations of its components, and regularly carries out absolute geomagnetic observations. Data products generated by an observatory are daily files of minute or second values of magnetic field variations and the data of absolute measurements (Hulot et al., 2010). ...
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The term “Big Data” has become very popular over the past decade. The frequency of its use in the research papers, reports, and broad press has been steadily increasing. This work describes the origin and development of the theory and practice of Big Data as a scientific discipline, outlines the main characteristics and methods for Big Data processing and analysis, discusses the formalism and family of Big Data V-characteristics, and presents the examples of the sources of the growing Big Data which have fundamental effect on the development of geophysics and related Earth sciences. The examples of the sources of Big Data in the Earth sciences are remote sensing, meteorology, geoecology (in terms of the global hierarchical network SMEAR (Stations Measuring Earth surfaces and Atmosphere Relations)), and seismic exploration. Besides, we discuss seismic monitoring data which can become Big Data when combined with other geophysical information and consider geomagnetic data which are not Big Data but nevertheless have a great scientific value.
... The internal field in terms of the Lowes-Mauersberger spectrum has its characteristic "knee" (Jackson, 1990) (see Fig. 1). This L-shape curve represents not only the energy with respect to a degree, but it also demonstrates that the two internal fields are substantially separated with respect to depth (Hulot et al., 2010). ...
... In the context of the internal field composed from the core and the lithospheric field, a key question is how the core and the lithospheric field mask each other (Langel and Estes, 1982;Hulot et al., 2010). Deciphering these fields is a classical problem and it cannot be resolved with a single data set (Jackson, 1990). ...
... The long-wavelength part (green) and the short wavelength part (blue) cross near degree 17. Although each part of the spectrum is not related to a particular source, the spectrum of the high-pass component seems to be close to the estimates based on different ideas (Jackson, 1990, fig. 2), (Hulot et al., 2010, fig. 14), (Thébault et al., 2009, fig. ...
Article
In most cases, the magnetic field anomalies from satellite data and models are determined by using a cut-off degree that splits the Earth's internal magnetic field (supposed to be of the core and lithospheric origin) into long-wavelength and a short-wavelength parts. This practice allows to effectively compare the signal of both components with other models and controls the signal content as well. In this study an alternative approach is followed to provide the components in long and short wavelengths without cutting the spectrum. Instead, we seek iteratively for the signal loss when the magnetic signal (from degree 1 to the maximum degree of the model) is propagated from the core-mantle boundary to satellite altitude. The problem is generally non-unique, it is required that the signal fit has to follow the slope of the geomagnetic spectrum over the lowest degrees (the degrees least affected by the magnetic lithosphere). The tool operates in the spatial domain – the spectral slope criterion is met after the procedure ends by selecting an appropriate solution. The method can be applied to the vector components individually as soon as they are given in the Earth-fixed Earth-centered frame, for which the integral equation is valid. The obtained magnetic anomalies have different spectral properties because the transition from the long wavelengths to the short wavelengths becomes smooth, although the appropriate number of iterations is questionable. It is found that the long-wavelength signal hands over the magnitude dominance to the short-wavelength part at around degrees 16 to 18.
... Дополнительным источником данных являются измерения литосферного магнитного поля. В масштабах от 250 до 3000 км оно может быть картировано на глобальном уровне по данным низкоорбитальных спутников [Hulot et al., 2010]. В масштабах меньше 250 км литосферное поле становится слишком малым, чтобы его можно было обнаружить на высоте пролета спутника. ...
... Полномасштабная наземная геомагнитная обсерватория регистрирует полную напряженность вектора геомагнитного поля и вариации его компонент, а также регулярно проводит абсолютные геомагнитные наблюдения. Продукция обсерватории -суточные файлы секундных или минутных значений вариаций геомагнитного поля, а также данные абсолютных измерений [Hulot et al., 2010]. ...
... и требует ручных операций. Такие измерения на обсерваториях выполняются один-два раза в неделю [Hulot et al., 2010]. ...
... Spatial and temporal geomagnetic field variations have been observed over different geological timescales. Ancient field measurements, mainly obtained from geological materials (sedimentary and igneous rocks), allow investigations of directional and intensity variability of the paleomagnetic field that result from processes operating in Earth's fluid core (see, e.g., Hulot et al., 2010). Particularly, information about paleosecular variation (PSV), long-term variations of the order of 10 5 -10 6 years (e.g., Johnson & McFadden, 2015), is essential to better understand temporal geomagnetic field evolution and to constrain numerical geodynamo models Coe & Glatzmaier, 2006;Davies et al., 2008;Meduri et al., 2021;Sprain et al., 2019). ...
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Investigations into long-term geomagnetic variations provide useful information regarding paleomagnetic field behavior. In this study, we assess the latitudinal structure of paleosecular variation (PSV) and the time-averaged field (TAF) for the Brunhes normal and Matuyama reverse chrons, and for the 0–10 Ma period, from an updated and reviewed paleodirectional database spanning the past 10 Myr. The new database comprises 2,543 paleomagnetic sites from igneous rocks, providing improvements in the geographic and temporal distributions of high-quality data relative to previous compilations. In addition, the new data collection differs considerably in application of strict selection criteria. Statistical analysis of the virtual geomagnetic pole (VGP) dispersion curve of Model G reveals a low latitudinal dependence of PSV for the last 10 Myr. For this period, we present a zonal TAF model based on the latitudinal distribution of inclination anomaly data. The best estimates found for axial quadrupole and octupole components were about 3% and 1% relative to axial dipole component, respectively. The new statistical models for the Brunhes and Matuyama chrons have different patterns in both PSV and TAF, in compliance with earlier studies. Our quantitative assessments indicate an apparent hemispheric PSV asymmetry, particularly in the Brunhes chron, with a stronger latitudinal signature in the southern hemisphere compared to the north. These findings suggest that equatorial PSV asymmetry, that has previously been found in modern, historical and millennial scale geomagnetic models, has persisted over the past 780 ka.
... The MM variations over long time scales are determined by complex geodynamic processes in the liquid core of the Earth (Hulot et al., 2010). Periods of 20-50 million years are distinguished as the main periods. ...
... Merci mon Ange ! Haller, 1971 ;Higgins et al., 1981 ;Sønderholm & Jepsen, 1991 ;Kontak et al., 2001 ;Higgins et al., 2008 ;Hulot et al., 2010) Les couleurs correspondent à la charte stratigraphique internationale. La bande noire et blanche correspond à l'échelle magnétostratigraphique. ...
... Q. : Quaternaire (d'après e.g. Talwani & Eldholm, 1977 ;Eldholm, 1987 ;Tessensohn & Piepjohn, 2000 ;Engen et al., 2008 ;Hulot et al., 2010 ;Jokat et al., 2016) Paquette et al., 1985 ;Schlichtholz et Houssais, 1999 ;Fahrbach et al., 2001, transect C). ...
... : Silurien (d'après e.g. Haller, 1971 ;Higgins et al., 1981 ;Sønderholm & Jepsen, 1991 ;Kontak et al., 2001 ;Higgins et al., 2008 ;Hulot et al., 2010). ...
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(Diaporama disponible : https://www.terres-du-passe.com/page-153-soutenance-de-these-2021.htm) Ce travail présente une analyse des environnements sédimentaires marins profonds des mers nordiques à l’interface de l’Atlantique nord et de l’Arctique (mers du Groenland, de Norvège, de Barents et d’Islande) au cours du dernier million d’années. Il se base sur une base de données acoustiques (bathymétrie, imagerie multifaisceau) et sédimentologique (carottes calypso) issues de deux campagnes réalisées par le Shom. Les enregistrements sédimentaires ont montré une très grande variabilité des processus de sédimentation en jeu dans ces mers en fonction des périodes climatiques, avec notamment une sédimentation glaciomarine, gravitaire, contouritique, et hémipélagique. Ils ont également permis de se concentrer sur la chronologie des périodes de développement ou de retrait des calottes continentales périphériques (calotte du Groenland, calotte Fennoscandie et calotte de Barents et Svalbard), et du couvert de glace de mer. Une étude stratigraphique détaillée a été réalisée sur la base de différents outils (datations radiocarbones, géochimie isotopique, géochimie élémentaire, biostratigraphie sur microfossiles et nannofossiles calcaires, et analyses sédimentologiques). La reconstitution de l’historique d’évolution des apports sédimentaires et des processus responsables de ces apports depuis le Quaternaire moyen (début de la Mid-Pleistocene Transition, MPT) jusqu’à l’Holocène terminal, a permis de mieux caractériser l’impact des variations d’extension des calottes continentales sur la sédimentation des mers nordiques, mais aussi d’identifier les périodes de forte influence du couvert de glace Arctique (y compris calotte potentielle en maxima glaciaire) sur les mers nordiques, et les variations de l'influence des courants de surface et de fond dans la zone nord et la zone sud de ces bassins boréaux. Notamment, les variations d’influences des eaux de surface chaudes et salées de l’Atlantique nord ont pu être identifiées pour certaines périodes de temps.