Paleomagnetic Records and Geomagnetic Reversals

Paleomagnetic records derive from the natural magnetisation preserved in volcanic rocks, sedimentary deposits and archaeological materials. These archives capture both the direction and intensity of the Earth’s magnetic field through geological time. Analysis of directional changes reveals episodes when the geomagnetic poles wander across the globe and, at intervals of several hundred thousand years, undergo full polarity reversals in which north and south magnetic poles swap. Measurements of relative palaeointensity trace fluctuations in field strength that often accompany directional transitions and excursions. Such records are essential for establishing precise geological timescales, reconstructing past plate motions and discerning the dynamics of the geodynamo in the Earth’s liquid outer core. Understanding the timing, duration and multi‐stage nature of reversals provides insight into core–mantle interactions, fluid flow patterns and the factors that control field stability. Beyond fundamental geophysics, palaeomagnetic data underpin applications in basin correlation, archaeological dating, critical mineral exploration and assessments of how variations in cosmic‐ray flux may influence climate and biological systems.

Research from Nature Portfolio

Novel work has demonstrated that organic biomarkers extracted from Pleistocene outcrops can survive diagenesis and yield sea‐surface temperature estimates that align closely with coeval magnetic stratigraphy, indicating that terrestrial rock sequences may complement sediment cores for global correlation of glacial–interglacial cycles. High‐resolution loess records across the last geomagnetic reversal reveal that weakening of the dipole field by more than 75% triggered millennial‐scale increases in cosmic‐ray flux, which in turn intensified the winter monsoon through enhanced low‐cloud albedo and greater land–ocean temperature gradients. Geological evidence from pollen assemblages supports the umbrella‐effect hypothesis, showing that field minima coincided with greater terrestrial cooling than marine cooling during marine isotope stages associated with reversals, suggesting that cosmic‐ray–driven cloud processes modulated regional climates during polarity transitions.

Paleomagnetic Records and Geomagnetic Reversals publication trend

The graph below shows the total number of articles in paleomagnetic records and geomagnetic reversals across all publications each year (not limited to Nature Index journals).

Technical terms

Geomagnetic reversal: A change in the Earth’s magnetic field during which the positions of magnetic north and south are interchanged.

Palaeomagnetic record: The remanent magnetisation in geological or archaeological materials that registers the direction and strength of past magnetic fields.

Relative palaeointensity: An index of past geomagnetic field strength inferred from magnetic properties of rocks or sediments, calibrated by laboratory demagnetisation procedures.

Virtual geomagnetic pole (VGP): The reconstructed position of the geomagnetic pole derived from the inclination and declination of magnetisation in a sample.

Be‐ratio: The proportion of cosmogenic beryllium isotopes (^10Be/^9Be) in sediments, used to infer variations in cosmic‐ray flux and geomagnetic field intensity.

References

1. Biomarkers in the rock outcrop of the Kazusa Group reveal palaeoenvironments of the Kuroshio region. Communications Earth & Environment (2021).
2. Intensified East Asian winter monsoon during the last geomagnetic reversal transition. Scientific Reports (2019).
3. Geological support for the Umbrella Effect as a link between geomagnetic field and climate. Scientific Reports (2017).
4. Constraining the age of the last geomagnetic reversal from geochemical and magnetic analyses of Atlantic, Indian, and Pacific Ocean sediments. Earth and Planetary Science Letters (2019).
5. A full sequence of the Matuyama–Brunhes geomagnetic reversal in the Chiba composite section, Central Japan. Progress in Earth and Planetary Science (2020).