Valet Jean-Pierre, Meynadier Laure, Guyodo Yohan
Géomagnétisme et Paléomagnétisme (UMR CNRS 7577), Institut de Physique du Globe de Paris, 4 Place Jussieu, 75252 Paris Cedex 05, France.
Nature. 2005 Jun 9;435(7043):802-5. doi: 10.1038/nature03674.
Independent records of relative magnetic palaeointensity from sediment cores in different areas of the world can be stacked together to extract the evolution of the geomagnetic dipole moment and thus provide information regarding the processes governing the geodynamo. So far, this procedure has been limited to the past 800,000 years (800 kyr; ref. 3), which does not include any geomagnetic reversals. Here we present a composite curve that shows the evolution of the dipole moment during the past two million years. This reconstruction is in good agreement with the absolute dipole moments derived from volcanic lavas, which were used for calibration. We show that, at least during this period, the time-averaged field was higher during periods without reversals but the amplitude of the short-term oscillations remained the same. As a consequence, few intervals of very low intensity, and thus fewer instabilities, are expected during periods with a strong average dipole moment, whereas more excursions and reversals are expected during periods of weak field intensity. We also observe that the axial dipole begins to decay 60-80 kyr before reversals, but rebuilds itself in the opposite direction in only a few thousand years.
来自世界不同地区沉积物岩芯的相对古地磁强度独立记录可以堆叠在一起，以提取地磁偶极矩的演变，从而提供有关地球发电机控制过程的信息。到目前为止，这一过程仅限于过去80万年（800 kyr；参考文献3），其中不包括任何地磁反转。在此，我们展示了一条复合曲线，该曲线显示了过去200万年中偶极矩的演变。这一重建结果与用于校准的火山熔岩得出的绝对偶极矩高度吻合。我们发现，至少在这一时期，在没有反转的时期，时间平均场更高，但短期振荡的幅度保持不变。因此，在平均偶极矩较强的时期，预计极低强度的间隔较少，因此不稳定性也较少，而在弱场强时期，预计会有更多的偏移和反转。我们还观察到，轴向偶极在反转前6万至8万年开始衰减，但仅在几千年内就会在相反方向重新形成。
