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Bibliographies thématiques / Geomagnetic field variations and reversals

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Littérature scientifique sur le sujet « Geomagnetic field variations and reversals »

Auteur : Grafiati

Publié le 10 mars 2023

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Articles de revues sur le sujet "Geomagnetic field variations and reversals"

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Kocharov, G. E., A. V. Blinov, A. N. Konstantinov, and V. A. Levchenko. "Temporal 10Be and 14C Variations: A Tool for Paleomagnetic Research." Radiocarbon 31, no. 2 (1989): 163–68. http://dx.doi.org/10.1017/s0033822200044829.

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Temporal variations of cosmogenic radionuclide atmospheric concentrations can be caused by such global phenomena as solar activity and geomagnetic field changes as well as atmospheric circulation processes. These causes can be distinguished by the comparison of several isotope records corresponding to the same time period. We discuss a possibility for reconstructing the geomagnetic moment during the last 30,000 years from the comparison of 10Be and 14C concentrations in terrestrial archives. The results agree with conventional paleomagnetic data and promise to enrich our knowledge of geomagnetic field variations and reversals.

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Kočí, Alois, and A. Janáčková. "Variations of the geomagnetic field at the time of reversals." Studia Geophysica et Geodaetica 29, no. 3 (1985): 280–89. http://dx.doi.org/10.1007/bf01638439.

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Dobretsov, N. L., D. V. Metelkin, and A. N. Vasilevskiy. "Typical Characteristics of the Earth’s Magnetic and Gravity Fields Related to Global and Regional Tectonics." Russian Geology and Geophysics 62, no. 1 (2021): 6–24. http://dx.doi.org/10.2113/rgg20204261.

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Abstract —We present a summary and analysis of current views on the magnetic and gravity fields of the Earth as a reflection of global and regional tectonic processes. The discussion concerns the probable interconnection between the distribution of the geomagnetic field characteristics, gravity anomalies and the manifestations of mantle plume magmatism as the most remarkable geologic indicator of deep geodynamics. We demonstrate that the distribution of the characteristics of the main geomagnetic field has a qualitative similarity to anomalies of the gravity field. Brief variations of the geomagnetic field are due to high-frequency oscillations in the ionosphere, do not affect the general state of the field, and are useless when considering issues of global tectonics. On the contrary, variations with long periodicities, first of all geomagnetic reversals, can be among the main indicators of the evolution of the geodynamo – the heat mechanism controlling the entire series of global tectonic processes. The frequency of reversals is determined by the intensity of mantle plumes that cause the cooling of the core, increase the convection rate in the asthenosphere, and respectively, the periodic changes in the tectonosphere. We assume the existence of three modes of behavior for this system. The first one corresponds to steady convection, in which reversals are extremely rare or do not happen at all. These episodes – superchrons – compose no more than 20% of the duration of the Phanerozoic. The second mode occurs significantly more often in the geologic history and is characterized by active convection with frequent reversals happening at least once every 5 Myr. Finally, the third mode, which is rare for the Phanerozoic but was probably more prevalent in the early Precambrian, corresponds to hyperactive turbulent convection, when the frequency of reversals reached 20 and possibly more during one million years. Although the demonstrated qualitative similarity in the position of extreme values of the main geomagnetic field, the centers of free air gravity anomalies, and manifestations of large igneous provinces does not yet have a credible explanation, we consider it to be fundamental and requiring special study and detailed elaboration.

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Maffei, Stefano, Philip W. Livermore, Jon E. Mound, Sam Greenwood, and Christopher J. Davies. "Fast Directional Changes during Geomagnetic Transitions: Global Reversals or Local Fluctuations?" Geosciences 11, no. 8 (2021): 318. http://dx.doi.org/10.3390/geosciences11080318.

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Paleomagnetic investigations from sediments in Central and Southern Italy found directional changes of the order of 10∘ per year during the last geomagnetic field reversal (which took place about 780,000 years ago). These values are orders of magnitudes larger than what is expected from the estimated millennial timescales for geomagnetic field reversals. It is yet unclear whether these extreme changes define the timescale of global dipolar change or whether they indicate a rapid, but spatially localised feature that is not indicative of global variations. Here, we address this issue by calculating the minimum amount of kinetic energy that flows at the top of the core required to instantaneously reproduce these two scenarios. We found that optimised flow structures compatible with the global-scale interpretation of directional change require about one order of magnitude more energy than those that reproduce local change. In particular, we found that the most recently reported directional variations from the Sulmona Basin, in Central Italy, can be reproduced by a core-surface flow with rms values comparable to, or significantly lower than, present-day estimates of about 8 to 22 km/y. Conversely, interpreting the observations as global changes requires rms flow values in excess of 77 km/y, with pointwise maximal velocities of 127 km/y, which we deem improbable. We therefore concluded that the extreme variations reported for the Sulmona Basin were likely caused by a local, transient feature during a longer transition.

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Merrill, R. T., and P. L. McFadden. "Secular variation and the origin of geomagnetic field reversals." Journal of Geophysical Research 93, B10 (1988): 11589. http://dx.doi.org/10.1029/jb093ib10p11589.

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Ryan, David A., and Graeme R. Sarson. "A coupled low order dynamo/turbulent shell model for geomagnetic field variations and reversals." Physics of the Earth and Planetary Interiors 188, no. 3-4 (2011): 214–34. http://dx.doi.org/10.1016/j.pepi.2011.09.003.

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Ultré-Guérard, Pascale, and José Achache. "Core flow instabilities and geomagnetic storms during reversals: The Steens Mountain impulsive field variations revisited." Earth and Planetary Science Letters 135, no. 1-4 (1995): 91–99. http://dx.doi.org/10.1016/0012-821x(95)00149-7.

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MOCHIZUKI, Nobutatsu, and Hideo TSUNAKAWA. "Geomagnetic Field Variations at the Beginning of the Polarity Reversal." Journal of Geography (Chigaku Zasshi) 114, no. 2 (2005): 194–200. http://dx.doi.org/10.5026/jgeography.114.2_194.

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Pal, Poorna C. "The palaeogeomagnetic field strength, variations in reversal frequency, and geomagnetic dynamo models." Geophysical & Astrophysical Fluid Dynamics 44, no. 1-4 (1988): 189–205. http://dx.doi.org/10.1080/03091928808208885.

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Abrahamsen, Niels, and Peter W. Readma. "Geomagnetic secular variation in Late Weichselian Allerød sediments from Nr. Lyngby (Denmark)." Bulletin of the Geological Society of Denmark 44 (March 15, 1997): 45–58. http://dx.doi.org/10.37570/bgsd-1998-44-03.

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Palaeomagnetic measurements on 400 specimens from lake sediments exposed in the cliff of the classic Late Glacial Allerød site at Nørre Lyngby in North Jutland, Denmark, are presented. Two profiles in the 7 m sequence of sand, silt and gyttja, spanning the time interval between c. 12 000 and c. 10 700 BP show about 5 cycles in the declination and about 2 cycles in inclination. Secular variation features as observed at this site are also recognizable at sites in southern Sweden and Soviet Karelia. Comparisons with Holocene records indicate that the short time-scale behaviour (i.e. < 103 y) of the geomagnetic field appears to have been similar since 14 000 BP, i.e. for a period considerably longer than the timescale of the variations themselves, thus suggesting that this type of behaviour is a permanent feature of the geomagnetic field. These secular variation features may be useful in local as well as more regional stratigraphical correlations for the Late Glacial and Holocene on a much more detailed timescale than is obtained from the magnetic reversal timescale used for older materials.

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