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Contribution to the high resolution study of the paleomagnetic field recorded in marine cores over the last 35 ka, bias and climatic signature
Surprisingly, the variations of the intensity of the Earth magnetic field remain very poorly constrained during the period 35ka – 5ka. This period is crucial because it allows access to the variability and therefore to the characteristic time of the geomagnetic dipole. The focus of the Phd is to study the magnetic, sedimentary and climatic signals of several marine cores with high sedimentation rates which have been selected on the basis of their isotopic stratigraphy. The examination of the reference curves for the last 80 kyr in the North Atlantic and the South Atlantic (respectively NAPIS and SAPIS) shows significant disparities between the two hemispheres for the 20-30 kyr period while the variations of the magnetic field should be global at the considered scale. There are also inconsistencies with the paleointensity curves deduced from the variations of cosmogenic isotopes derived from the 10Be/9Be ratio at the same ages. The causes of these discrepancies remain to be established.
The objective of the thesis is therefore to produce high-resolution regional reference curves in areas devoid of data. In parallel, possible excursions will be sought. To achieve the best resolution (Phillipe et al., 2018), a mini-cube sampling protocol will be tested for the first time.
The questions addressed are the following:
– how to explain the inconsistency of the intensity curves of the magnetic field between the North Atlantic and the South Atlantic between 20 and 30 ka?
– can we build a reference “master curve” for the South-East Pacific region despite the very pronounced monsoon effect in this region involving changes in lithology?
– Do the upheavals of the deep sea currents at the end of the glacial and during the deglaciation have an impact on the signals?
– What is the origin of the inconsistencies between the magnetic and cosmogenic signals (10Be/9Be) and can we overcome them, or even correct them?
– Determine the origin and consistency of the geomagnetic excursions of the 5-35 ka period.