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.
Highlights
The dominant dipolar component of the Earth’s magnetic field has been steadily weakening for at least the last 170 years
Only records using well-dated manmade baked artefacts such as pottery, kilns and copper slags attained the temporal resolution needed to reveal the occurrence of short-lived rapid fluctuations in geomagnetic field intensity
As a consequence of their differing composition and thermal history, the success rate in obtaining reliable estimates of the geomagnetic field intensity is much lower for lavas than for archaeological artefacts
Summary
The dominant dipolar component of the Earth’s magnetic field has been steadily weakening for at least the last 170 years. 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 B1,000 years ago, qualitatively similar to behaviour observed 200 years earlier in Europe and 500 years later in Mesoamerica. Evidence that the geomagnetic field has exhibited numerous intense, short-lived, regional maxima in intensity at various times and locations in the last few thousand years is rapidly accumulating: records from Europe[1,2], Mesoamerica[3,4], West Africa[5] and the Middle-East[6,7,8] show at least one intensity high These highly intriguing features are poorly understood because the limited number and uneven geographical distribution of reliable archaeointensity records hamper a meaningful analysis. We conclude that these rapid regional variations in the intensity of the Earth’s magnetic field result from spatially and temporally non-uniform geomagnetic phenomena that are presently enigmatic in terms of their sources
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