Rapid regional perturbations to the recent global geomagnetic decay revealed by a new Hawaiian record

Abstract

The dominant dipolar component of the Earth’s magnetic field has been steadily weakening for at least the last 170 years. Prior to these direct measurements, archaeomagnetic records show short periods of significantly elevated geomagnetic intensity. These striking phenomena are not captured by current field models and their relationship to the recent dipole decay is highly unclear. Here we apply a novel multi-method archaeomagnetic approach to produce a new high-quality record of geomagnetic intensity variations for Hawaii, a crucial locality in the central Pacific. It reveals a short period of high intensity occurring ~1,000 years ago, qualitatively similar to behaviour observed 200 years earlier in Europe and 500 years later in Mesoamerica. We combine these records with one from Japan to produce a coherent picture that includes the dipole decaying steadily over the last millennium. Strong, regional, short-term intensity perturbations are superimposed on this global trend; their asynchronicity necessitates a highly non-dipolar nature.

The multimethod palaeointensity approach applied to volcanics from Terceira: full-vector geomagnetic data for the past 50 kyr

“…The grain size selection is done at specimen level using a parameter that can be derived from the pseudo-Thellier experiments: B 1 2 ARM , half the value of the field that imparts the saturated ARM, in our experiments at 300 mT. Samples with a B 1 2 ARM between 23 and 63 mT can be reliably converted into absolute palaeointensities by a linear calibration relation (de Groot et al 2013). …”

“…The calibrated pseudo-Thellier technique (de Groot et al 2013) avoids thermally induced alteration that may occur in conventional palaeointensity methods. This relatively new method converts the outcome of relative pseudo-Thellier experiments (Tauxe et al 1995) on lavas into absolute estimates of the Earth's palaeofield.…”

“…This multispecimen method (MSP) was later refined by Fabian & Leonhardt (2010) to account for potential changes in the magnetic domain state during the experiment. To avoid thermally induced alteration altogether, a relative palaeointensity technique frequently used on sediments, the pseudo-Thellier method, was recently calibrated to provide absolute estimates of the palaeofield's intensity from volcanic samples and proved to be a valuable addition to the palaeointensity toolbox (de Groot et al 2013).…”

“…The number of reliable palaeointensity estimates arising from a single study can be increased by (1) sampling cooling units at various locations and/or at different depths in the unit (de Groot et al 2014) and (2) implementing several of the aforementioned palaeointensity techniques in one study (de Groot et al 2013. Studies adopting this approach yielded reliable estimates of the palaeofield's intensity for 60-70 per cent of all possible flows/ages in their data sets, contrasting with the success rate of ∼20 per cent for classical intensity approaches (e.g.…”

Magnetic force microscopy reveals meta-stable magnetic domain states that prevent reliable absolute palaeointensity experiments

“…Over the past decades, various tests and protocols have been proposed to identify and (partially) overcome the MD effects during palaeointensity experiments [3][4][5][6][7][8][9][10][11][12] , but success rates of such experiments are still notoriously low [17][18][19][20] . It is even more disturbing that-in spite of extensive testing-palaeointensity experiments sometimes yield technically successful estimates of the palaeofield that actually over-or underestimate the palaeofield by tens of percent 6,21 .…”