Reassessment of the Mono Lake Excursion

莫诺湖之旅发生在大约35,000年前。它代表了地球磁场在其时空模式上经历了异常的、大规模的变化的最近一次，甚至可能在全球范围内改变为一种完全不同的配置，一种漂移状态。莫诺湖漂移是根据对加利福尼亚州莫诺湖湖泊沉积物的古地磁研究而定义的。这项研究解决了围绕莫诺湖之旅的几个悬而未决的问题。目前还没有与莫诺湖漂移相关的完整方向波形或古强度模式的记录，这些漂移超出了莫诺湖的类型地点。莫诺湖之旅的绝对年龄仍然存在合理的不确定性。北美西部(莫诺湖附近)深海沉积物中没有莫诺湖漂移的高分辨率记录，其氧同位素年代地层学可以将漂移与全球GISP2冰芯年代学、海因里希事件或丹斯加德/奥施格旋回联系起来。假设(就像我们所做的那样)莫诺湖远足比拉尚远足(约41,000年前的下一次更古老的远足)年轻约6000年，它们之间有什么关系(如果有关系的话)？目前的研究正在从俄勒冈州海岸外北太平洋东部的深海沉积物和南加州鲍德温湖的湖泊沉积物中恢复长期变化和古强度的古地磁记录。深海沉积物有与之相关的高分辨率氧同位素记录，湖泊记录有20多个放射性碳测年，包括莫诺湖/拉尚漂移间隔。初步的古地磁结果表明，莫诺湖漂移和更古老的拉尚漂移都存在于这两个记录中，其年龄与先前的估计一致。新的古地磁记录将与先前公布的北冰洋、北大西洋、菲律宾群岛和智利海岸边缘的莫诺湖/拉尚漂移间隔的远场古地磁记录相结合，以确定与莫诺湖漂移有关的全球磁场变化的时空模式。这些数据还将被用来建立一系列低阶球面调和模型，定量描述全球范围内的变化模式。这样的观测是测试变异性的地磁场时间尺度的概念、漂移的起源和性质以及它们与发电机行为的关系所必需的。这项研究使用了一名高中生、南加州大学研究生和博士后研究员进行测量，并帮助进行数据分析。最后的古地磁数据集和球谐分析将在PI的网站(http://earth.usc.edu/~slund))上提供，并转发给其他数据库倡议。

The Mono Lake Excursion occurred around 35,000 years ago. It represents the most recent time when the Earth's magnetic field has gone through an anomalous, large-scale change in its space/time pattern, perhaps even changing globally into a profoundly different configuration, an excursional state. The Mono Lake Excursion was defined from paleomagnetic studies of lacustrine sediments at Mono Lake, California. This study addresses several unresolved issues surrounding the Mono Lake Excursion. There is currently no record of the complete directional waveform or paleointensity pattern associated with the Mono Lake Excursion outside its type locality at Mono Lake. There is still legitimate uncertainty about the absolute age of the Mono Lake Excursion. There is no high-resolution record of the Mono Lake Excursion in deep-sea sediments from western North America (near Mono Lake), which have an oxygen-isotope chronostratigraphy that can tie the excursion to the global GISP2 ice-core chronology, Heinrich Events, or Dansgaard/Oeschger cyclicity. Assuming (as we do) that the Mono Lake Excursion is ~6000 years younger than the Laschamp Excursion (the next older excursion about 41,000 years ago), what is the relationship between them (if any)? The current study is recovering paleomagnetic records of secular variation and paleointensity from deep-sea sediments of the eastern North Pacific Ocean, off the Oregon coast, and lacustrine sediments from Baldwin Lake, Southern California. The deep-sea sediments have a high-resolution oxygen-isotope record associated with them and the lake record has more than 20 radiocarbon dates that bracket the Mono Lake/Laschamp Excursion interval. Preliminary paleomagnetic results indicate that the Mono Lake Excursion and the older Laschamp Excursion are present in both records with ages that are consistent with previous estimates. The new paleomagnetic records will be combined with previously published far-field paleomagnetic records of the Mono-Lake/Laschamp Excursion intervals from the Arctic Ocean, North Atlantic Ocean, Philippine Islands, and Chile coastal margin to define the space-time pattern of global field variability associated with the Mono Lake Excursion. These data will also be used to build a series of low-degree spherical harmonic models that quantitatively describe that pattern of variability on a global scale. Such observations are required to test concepts of geomagnetic field timescales of variability, the origin and nature of excursions, and their relationship to dynamo behavior.This study is using a high-school student, USC graduate student, and post-doctoral researcher to make measurements and help in the data analysis. The final paleomagnetic data sets and spherical harmonic analyses will be available at the PI's website (http://earth.usc.edu/~slund) and forwarded to other database initiatives.