Reassessment of the Mono Lake Excursion

莫诺湖之旅发生在大约35000年前。它代表了地球磁场在空间/时间模式上经历了一次异常的大规模变化，甚至可能在全球范围内转变为一种截然不同的配置，一种偏移状态。莫诺湖漂移是通过对加州莫诺湖湖泊沉积物的古地磁研究确定的。本研究解决了围绕莫诺湖游览的几个未解决的问题。目前在莫诺湖的莫诺湖漂移类型区域之外，还没有完整的定向波形或古强度模式的记录。关于莫诺湖游览的绝对年龄仍然存在合理的不确定性。在北美西部（靠近莫诺湖）的深海沉积物中没有高分辨率的莫诺湖漂移记录，这些沉积物的氧同位素年代学可以将该漂移与全球GISP2冰芯年代学、Heinrich Events或Dansgaard/Oeschger旋回联系起来。假设（就像我们做的那样）莫诺湖游览比拉尚游览（下一个更古老的游览大约41000年前）年轻6000年，它们之间的关系是什么（如果有的话）？目前的研究正在恢复北太平洋东部、俄勒冈海岸外的深海沉积物和南加州鲍德温湖的湖泊沉积物的古地磁长期变化和古强度的记录。深海沉积物有与之相关的高分辨率氧同位素记录，湖泊记录有超过20个放射性碳年代，涵盖了莫诺湖/拉尚漂移间隔。初步的古地磁结果表明，在这两个记录中都存在莫诺湖偏移和更老的拉尚偏移，其年龄与先前的估计一致。新的古地磁记录将与先前发表的来自北冰洋、北大西洋、菲律宾群岛和智利海岸边缘的Mono-Lake/Laschamp漂移间隔的远场古地磁记录相结合，以确定与Mono湖漂移相关的全球场变率的时空格局。这些数据还将用于建立一系列低度球谐模型，以定量地描述全球尺度上的这种变化模式。需要这样的观测来检验地磁场变异性的时间尺度、偏移的起源和性质以及它们与发电机行为的关系等概念。这项研究使用了一名高中生，南加州大学的研究生和博士后研究员进行测量并帮助进行数据分析。最终的古磁学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计划。

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.