Department of Earth and Environmental Sciences, Ludwig-Maximilians-Universitaet, 80333 Munich, Germany.
Geophysical Observatory Borok, Institute of Physics of the Earth, Russian Academy of Sciences, Yaroslavl Oblast, 151742 Borok, Russia.
Proc Natl Acad Sci U S A. 2023 Jun 20;120(25):e2220887120. doi: 10.1073/pnas.2220887120. Epub 2023 Jun 12.
Recovering the geomagnetic field strength in the past is key to understanding deep Earth dynamics and detecting potential geodynamo regimes throughout the history of Earth. To better constrain the predictive power of the paleomagnetic record, we propose an approach based on the analysis of the dependency between geomagnetic field strength and inclination (angle made by the horizontal with the field lines). Based on the outcomes of statistical field models, we show that these two quantities should correlate for a wide range of Earth-like magnetic fields, even with enhanced secular variation, persistent nonzonal components, and severe noise contamination. Focusing on the paleomagnetic record, we show that the correlation is not significant for the Brunhes polarity chron, what we ascribe to inadequate spatiotemporal sampling. In contrast, the correlation is significant for the 1 to 130 Ma interval, whereas it only marginally succeeds prior to 130 Ma when strict filters on both paleointensities and paleodirections are applied. As we cannot detect significant variations in the strength of the correlation over the 1 to 130 Ma interval, we conclude that the Cretaceous Normal Superchron may not be associated with enhanced dipolarity of the geodynamo. The strong correlation obtained prior to 130 Ma when strict filters are applied indicates that the ancient field may not be on average so different from the present-day field. If long-term fluctuations nevertheless existed, detecting potential geodynamo regimes during the Precambrian is currently impeded by the sparsity of high-quality data passing strict filters in both paleointensities and paleodirections.
恢复过去的地磁场强度对于理解地球深部动力学以及检测地球历史上潜在的地发电机状态至关重要。为了更好地约束古地磁记录的预测能力，我们提出了一种基于地磁场强度与倾斜（磁场线与水平面之间的夹角）之间依赖关系分析的方法。基于统计场模型的结果，我们表明这两个量应该在广泛的类地磁场范围内相关联，即使存在增强的长期变化、持续的非纬向分量和严重的噪声污染。关注古地磁记录，我们发现 Brunhes 极性时期的相关性不显著，我们将其归因于时空采样不足。相比之下，1 到 130 Ma 之间的相关性显著，而在应用严格的古强度和古方向滤波器之前，该相关性在 130 Ma 之前仅略有成功。由于我们无法检测到 1 到 130 Ma 之间相关性强度的显著变化，因此我们得出结论，白垩纪正常超静磁期可能与地发电机的偶极增强无关。在应用严格滤波器时，在 130 Ma 之前获得的强相关性表明，古磁场平均而言与现代磁场并没有太大的不同。如果确实存在长期波动，那么在古元古代检测潜在的地发电机状态目前受到通过严格滤波器的高质量数据在古强度和古方向上的稀疏性的阻碍。
