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Climatic and geomagnetic influences on the Lac du Bouchet palaeomagnetic SV record through the last 110 000 years

Physics of The Earth and Planetary Interiors
Publication Date
DOI: 10.1016/0031-9201(90)90046-z
  • Earth Science


Abstract Palaeomagnetic secular variation records stacked from five cores ∼ 20 m long extend back through the last glacial cycle to ∼ 100 000 years ago. The time-scale has been constructed from conventional and accelerator radiocarbon ages back to ∼ 45 Ka BP and beyond this by comprehensive pollen studies which identify forest and steppe cycles that have been related to marine oxygen isotopic stages 4 and 5. Spectral analyses of the intensity and directional records using both Fourier and maximum entropy methods reveal strong low-frequency components which fall in the range of the Milankovitch obliquity and precession periodicities (40-20 Ka). It is concluded that although part of this signal may have fed indirectly into the natural remanence via the influence of climatic change on sediment facies, part has been impressed directly by perturbation of the geomagnetic dynamo process at the core-boundary by variations in the Earth's obliquity and precession. These long periods envelop a well-defined pattern, registered also by the independent ‘Mackereth’ core stack back to 50 Ka BP, of irregular secular oscillations of the geodynamo with periods of a few thousands of years.

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