scholarly journals Synchronizing volcanic, sedimentary, and ice core records of Earth’s last magnetic polarity reversal

2019 ◽  
Vol 5 (8) ◽  
pp. eaaw4621 ◽  
Author(s):  
Brad S. Singer ◽  
Brian R. Jicha ◽  
Nobutatsu Mochizuki ◽  
Robert S. Coe
Keyword(s):  
Magnetic Field ◽  
Short Duration ◽  
Ice Core ◽  
Magnetic Polarity ◽  
Lava Flows ◽  
Polarity Reversal ◽  
Field Polarity ◽  
Reversal Process ◽  
Complex Process ◽  
Magnetic Polarity Reversal

Reversal of Earth’s magnetic field polarity every 105 to 106 years is among the most far-reaching, yet enigmatic, geophysical phenomena. The short duration of reversals make precise temporal records of past magnetic field behavior paramount to understanding the processes that produce them. We correlate new 40Ar/39Ar dates from transitionally magnetized lava flows to astronomically dated sediment and ice records to map the evolution of Earth’s last reversal. The final 180° polarity reversal at ~773 ka culminates a complex process beginning at ~795 ka with weakening of the field, succeeded by increased field intensity manifested in sediments and ice, and then by an excursion and weakening of intensity at ~784 ka that heralds a >10 ka period wherein sediments record highly variable directions. The 22 ka evolution of this reversal suggested by our findings is mirrored by a numerical geodynamo simulation that may capture much of the naturally observed reversal process.

Davis Creek silt, an Early Pleistocene or Late Pliocene deposit in the Cypress Hills of Saskatchewan

1989 ◽  
Vol 26 (1) ◽  
pp. 192-198 ◽  
Author(s):  
W. J. Vreeken ◽  
R. W. Klassen ◽  
R. W. Barendregt
Keyword(s):  
Volcanic Ash ◽  
Magnetic Polarity ◽  
Polarity Reversal ◽  
Early Pleistocene ◽  
The South ◽  
Glacial Deposits ◽  
Late Pliocene ◽  
Late Wisconsinan ◽  
Weathering Zone ◽  
Magnetic Polarity Reversal

Davis Creek silt is the informal name for a previously unreported loess and its reworked detritus encountered at several locations to the south of the east and centre blocks of the Cypress Hills. This unit intervenes between a pediment with an estimated age of 10 Ma and Late Wisconsinan glacial deposits. Because the unit has reversed magnetization, it is older than 788 ka, the astronomical age of the Matuyama–Brunhes magnetic polarity reversal. The unit also contains an undated volcanic ash from the Pearlette ash family that could represent the Mesa Falls (1.27 Ma) or the Huckleberry Ridge (2.02 Ma) ash bed. Davis Creek silt overlies an oxidized weathering zone and contains large secondary carbonate nodules near its truncated top that were, in places, reworked into a lag deposit or stone line before accumulation of the glacial overburden. At one location Davis Creek silt is separated from this overburden by a unit of cryoturbated gravelly loam with remnants of a reddish-yellow paleosolic B horizon.

scholarly journals Magnetic cycles of the planet-hosting star τ Bootis - II. A second magnetic polarity reversal

2009 ◽  
Vol 398 (3) ◽  
pp. 1383-1391 ◽  
Author(s):  
R. Fares ◽  
J.-F. Donati ◽  
C. Moutou ◽  
D. Bohlender ◽  
C. Catala ◽  
...  
Keyword(s):  
Magnetic Polarity ◽  
Polarity Reversal ◽  
Magnetic Cycles ◽  
Magnetic Polarity Reversal

scholarly journals Elevated paleomagnetic dispersion at Saint Helena suggests long-lived anomalous behavior in the South Atlantic

2020 ◽  
Vol 117 (31) ◽  
pp. 18258-18263 ◽  
Author(s):  
Yael A. Engbers ◽  
Andrew J. Biggin ◽  
Richard K. Bono
Keyword(s):  
Geomagnetic Field ◽  
Anomalous Behavior ◽  
Magnetic Polarity ◽  
South Atlantic ◽  
Polarity Reversal ◽  
The South ◽  
Geomagnetic Secular Variation ◽  
Core Dynamics ◽  
Geocentric Axial Dipole ◽  
Magnetic Polarity Reversal

Earth’s magnetic field is presently characterized by a large and growing anomaly in the South Atlantic Ocean. The question of whether this region of Earth’s surface is preferentially subject to enhanced geomagnetic variability on geological timescales has major implications for core dynamics, core−mantle interaction, and the possibility of an imminent magnetic polarity reversal. Here we present paleomagnetic data from Saint Helena, a volcanic island ideally suited for testing the hypothesis that geomagnetic field behavior is anomalous in the South Atlantic on timescales of millions of years. Our results, supported by positive baked contact and reversal tests, produce a mean direction approximating that expected from a geocentric axial dipole for the interval 8 to 11 million years ago, but with very large associated directional dispersion. These findings indicate that, on geological timescales, geomagnetic secular variation is persistently enhanced in the vicinity of Saint Helena. This, in turn, supports the South Atlantic as a locus of unusual geomagnetic behavior arising from core−mantle interaction, while also appearing to reduce the likelihood that the present-day regional anomaly is a precursor to a global polarity reversal.

Generation of waves by the solar magnetic field polarity reversal

Solar Physics ◽  
1995 ◽  
Vol 157 (1-2) ◽  
pp. 31-44 ◽  
Author(s):  
A. D. Pataraya ◽  
T. V. Zaqarashvili
Keyword(s):  
Magnetic Field ◽  
Solar Magnetic Field ◽  
Polarity Reversal ◽  
Field Polarity

Cosmic-Ray Transport in Heliospheric Magnetic Structures. III. Implications of Solar Magnetograms for the Drifts of Cosmic Rays

2021 ◽  
Vol 922 (2) ◽  
pp. 124
Author(s):  
Andreas Kopp ◽  
Jan Louis Raath ◽  
Horst Fichtner ◽  
Marius S. Potgieter ◽  
Stefan E. S. Ferreira ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Solar Cycle ◽  
Cosmic Rays ◽  
Boundary Conditions ◽  
Large Scale ◽  
Cosmic Ray ◽  
Magnetic Polarity ◽  
Solar Observatory ◽  
Field Polarity ◽  
Heliospheric Magnetic Field

Abstract The transport of energetic particles in the heliosphere is reviewed regarding the treatment of their drifts over an entire solar cycle including the periods around solar maximum, when the tilt angles of the heliospheric current sheet increase to large values and the sign of the magnetic polarity changes. While gradient and curvature drifts are well-established elements of the propagation of cosmic rays in the heliospheric magnetic field, their perturbation by the solar-activity-induced large-scale distortions of dipole-like field configurations and by magnetic turbulence is an open problem. Various empirical or phenomenological approaches have been suggested, but either lack a theory-based motivation or have been shown to be incompatible with measurements. We propose a new approach of more closely investigating solar magnetograms obtained from GONG maps, leading to a new definition of (i) tilt angles that may exceed those provided by the Wilcox Solar Observatory during high activity and of (ii) a “noninteger sign” that can be used to reduce the drifts during these periods as well as to provide a refinement of the magnetic field polarity. The change of sign from A < 0 to A > 0 of solar cycle 24 can be in this way localized to occur between Carrington Rotations 2139 and 2140 in mid 2013. This treatment is fully consistent in the sense that the transport modeling uses the same input data to formulate the boundary conditions at the heliobase as do the magnetohydrodynamic models of the solar wind and the embedded heliospheric magnetic field that exploit solar magnetograms as inner boundary conditions.

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