Cosmogenic 10Be production records reveal dynamics of geomagnetic dipole moment (GDM) over the Laschamp excursion (20–60 ka)
Cosmogenic 10Be production records reveal dynamics of geomagnetic dipole moment (GDM) over the Laschamp excursion (20–60 ka)
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DOI：
10.1016/j.epsl.2020.116547
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发表时间：
2020-11
影响因子：
5.3
通讯作者：
Q. Simon;N. Thouveny;D. Bourlès;J. Valet;Franck Bassinot
中科院分区：
文献类型：
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作者：
Q. Simon;N. Thouveny;D. Bourlès;J. Valet;Franck Bassinot
准确记录地磁变化的幅度和节奏是了解触发地磁偏移和反转机制的先决条件。我们提出了新的自生 10 Be/9 Be 比值（Be 比值）结果，涵盖来自赤道核心 MD05-2920 的 60-20 ka 时间间隔。最显着的 Be 比率峰值位于该序列中记录的主要相对古强度 (RPI) 最小值以上 18 厘米。这些被解释为与大约 41ka 的 Laschamp 偏移相关的地磁偶极矩 (GDM) 减少的两个独立记录。地层偏移可归因于沉积后磁化锁定过程，导致 1.6 ka 的时间延迟。 Be 比率和 RPI 记录显示偶极低点之前和之后具有可比性的不对称行为。 Be 比率记录与其他三个系列相结合，构建了 10 Be 古生产变化的全球记录。该汇编表明低纬度和中纬度数据集具有很强的一致性，并且与极地地区的 10 Be 通量记录进行比较，完全支持 Laschamp 期间全球大气 10 Be 产量翻倍的假设。使用理论模型和使用熔岩流上测量的绝对古强度重建 GDM 值，将 Be 比率叠加转换为 GDM。两种方法都提供相似的结果。从这种方法得出的偶极矩记录（BeDM 20-60）显示出以下特征：高场值（> 11× 10 22 Am 2），然后急剧的两步偶极子下降，直到在 Laschamp 偏移时在 41.6 和 40.9 ka 之间达到最小值（1.8±0.7× 10 22 Am 2）。 GDM 部分恢复到约 6.3× 10 22 Am 2 的值，并在此范围内振荡，没有显示出任何可能与 38-20 ka 时间间隔内报告的偏移（例如莫诺湖偏移）相关的急剧下降。
Documenting accurately amplitude and rhythms of geomagnetic variations is a prerequisite to understand the mechanisms triggering geomagnetic excursions and reversals. We present new authigenic 10 Be/9 Be ratio (Be ratio) results covering the 60–20 ka time interval from equatorial core MD05-2920. The most significant Be ratio peak is located 18 cm above the main relative paleointensity (RPI) minimum recorded in this sequence. These are interpreted as two independent recordings of the geomagnetic dipole moment (GDM) decrease linked to the Laschamp excursion dated at ca 41 ka. The stratigraphic offset is assignable to post-depositional magnetization lock-in processes resulting in time delay of 1.6 ka. The Be ratio and RPI records show comparable asymmetric behavior before and after the dipole low. The Be ratio record is combined with three other series to construct a global record of 10 Be paleoproduction variations. This compilation demonstrates the strong coherence of low and mid latitudes data sets and its comparison with 10 Be-flux records from polar regions fully supports the hypothesis of a global atmospheric 10 Be production doubling during the Laschamp. The Be ratio stack is converted in terms of GDM using both a theoretical model and a reconstruction of GDM values using absolute paleointensities measured on lava flows. Both methods provide similar results. The dipole moment record derived from this approach (BeDM 20–60) shows the following characteristics: high field values (> 11× 10 22 Am 2) prior to a sharp two-steps dipole decrease until reaching minimum values (1.8±0.7× 10 22 Am 2) between 41.6 and 40.9 ka at the time of the Laschamp excursion. The GDM partly recovers up to values of∼ 6.3× 10 22 Am 2, and oscillates in this range, without showing any sharp decreases that could be associated with excursions reported within the 38–20 ka time interval (eg the Mono Lake excursion).