Abstract
The rapid decrease of the geomagnetic field intensity in the last centuries has led to speculations that an attempt to a reversal or an excursion might be under way. Here we investigate this hypothesis by examining past records of geomagnetic field intensity obtained from sedimentary cores and from the study of cosmogenic nuclides. The selected records describe geomagnetic changes with an unprecedented temporal resolution between 20 and 75 kyr B.P. We find that some aspects of the present-day geomagnetic field have some similarities with those documented for the Laschamp excursion 41 kyr ago. Under the assumption that the dynamo processes for an eventual future reversal or excursion would be similar to those of the Laschamp excursion, we tentatively suggest that, whilst irreversible processes that will drive the geodynamo into a polarity change may have already started, a reversal or an excursion should not be expected before 500 to 1000 years.
Highlights
Since the first measurements made by the observatories, the Earth’s magnetic field intensity has been diminishing at an average rate of 5% per century, about an order of magnitude faster than the rate expected for simple decay by diffusion
Gubbins (1987) noted that a patch of flux occurring below the southern tip of Africa had opposite sign to that expected for a dipole field in the Southern Hemisphere, when extrapolated at the core mantle boundary
The very high resolution GLOPIS-75 record of past geomagnetic field intensity over the last 75 kyr does not provide any undisputable information on future evolution of the field
Summary
Since the first measurements made by the observatories, the Earth’s magnetic field intensity has been diminishing at an average rate of 5% per century, about an order of magnitude faster than the rate expected for simple decay by diffusion. Gubbins (1987) noted that a patch of flux occurring below the southern tip of Africa had opposite sign to that expected for a dipole field in the Southern Hemisphere, when extrapolated at the core mantle boundary (the South Atlantic Anomaly or SAA). He suggested that “the present fall of the dipole field is directly related to the intensification and southward migration of this and other similar patches and that the fall may occasionally leads to polarity reversal.”. They postulate “that the present magnetic state of the Earth may be one in which the geodynamo operates before reversing,” consistent with, but with a much better spatial resolution than Gubbins’ (1987) suggestion
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