The origin of the terrestrial magnetic field lies in the interior of the planet. In the deepest part of the Earth is the core that, in its outermost part, is mainly composed of molten iron and nickel. Due to convective currents, electric currents are produced in this moving metallic fluid, which in turn generates a magnetic field.
We cannot go down into these deep regions, but one way to understand what happens there is to study the magnetic field that rises to the surface and extends out of our planet.
Although the phenomena that take place in the depths of the Earth are complex, the reality is that the result, seen from the surface, suggests that the whole has a behavior similar to that of a magnet, with the poles slightly deviated from the geographic poles that marks the axis of rotation of the planet. Thus, the interior is usually presented as a magnet whose south pole points to the terrestrial north pole and vice versa. Like all magnets, the south pole attracts the north pole of another magnet placed nearby, something that we can easily check with the magnetic needle of a compass. The compass needle always points in the direction of the Earth’s magnetic poles.
However, as we have said, the Earth’s interior is not rigid and the electrical currents that are produced inside it vary with time, a variation that translates into orientation changes and a displacement of the magnetic poles. The magnetic field created is not uniform over the entire earth’s surface either, there are regions or patches where the intensity of the total magnetic field is strengthened or weakened. It has been shown that, during the last century, the magnetic North Pole has moved more than a thousand kilometers from northern Canada to northern Siberia, a displacement that, according to recent work based on geomagnetic measurements, has been largely determined. by the influence of two competing flow patches, located below Canada and Siberia.
Particles with iron ores and other metals, when deposited on the ocean floor, behave like small compasses oriented in the direction of the current magnetic field. By being buried under other subsequent sediments, these particles are imprisoned without the possibility of moving, conserving the direction of the Earth’s magnetic field at the time they were deposited. In this way, if the magnetic North Pole changes position, the different sediments indicate the direction in which these changes occur.
To understand whether the increase and decrease of magnetic flux patches have marked the trajectory of the geomagnetic paleo-poles in the past, a team of researchers including Saioa Arquero Campuzano, a researcher at the Complutense University of Madrid and invited in Talking to Scientists, has carried out an investigation of sediments extracted from the northwestern margin of the Barents Sea and the western margin of Spitsbergen (Arctic) accumulated over 22,000 years.
The research, carried out by Chiara Caricchi, Saioa Arquero and their colleagues, has made it possible to determine the trajectory of the virtual geomagnetic pole (VGP) during the 22,000 years spanning the sediments and compare it with maps of the radial component of the geomagnetic field at the core-mantle boundary, obtained by other means.
The detected path reveals an irregular behavior in the movement of the magnetic North Pole that includes centuries during which the position has been stable and centuries whose movement has accelerated. Paths indicating both clockwise and anti-clockwise movement have also been detected. The detected path seems to follow the appearance of patches of normal magnetic flux, especially those located beneath the Siberian and Canadian areas, but also those that can cause peculiar paleomagnetic features, such as the one known as the Levantine Iron Age Anomaly.
I invite you to listen to the explanations of Saioa Arquero Campuzano, currently a researcher at the Department of Earth Physics and Astrophysics at the Complutense University of Madrid.
References:
Chiara Caricchi, Saioa A. Campuzano et al; Reconstruction of the Virtual Geomagnetic Pole (VGP) path at high latitude for the last 22 kyr: The role of radial field flux patches as VGP attractor.
Earth and Planetary Science Letters, ISSN: 0012-821X, Vol: 595, Page: 117762
S.A. Campuzano et al; New perspectives in the study of the Earth’s magnetic field and climate connection: The use of transfer entropy. PLOS ONENovember 2018