Holocene Paleomagnetic Secular Variation (Directions and Intensity) from Southast Alaska

阿拉斯加东南部的全新世古地磁长期变化（方向和强度）

• 批准号: 0711584
• 负责人: Joseph Stoner
• 金额: $ 32.5万
• 依托单位: Oregon State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2007
• 资助国家: 美国
• 起止时间: 2007-08-01 至 2010-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0711584&HistoricalAwards=false
• 关键词: Holocene; Paleomagnetic; Secular; Variation; Directions

Observations of the historical geomagnetic field and its secular variations from a wide variety of sources reveal transient and persistent geomagnetic features. Persistent features include the subdued secular variation in the Pacific relative to the Atlantic hemisphere, and regions of concentrated geomagnetic flux over Canada and Siberia at ~60° N latitude. Transient historical features include movement of the North Magnetic Pole and a growing region of reversed magnetic flux at the core/mantle boundary below the South Atlantic. Along with the present dipole intensity decay rate of 5% per century (five times the free decay rate), these observations have led some researchers to speculate that the geomagnetic field may be heading toward a reversal or an excursion. The question of whether the recently accelerated dipole decay is likely to continue is important to society because the magnetic field shields the earth from cosmic ray bombardment, with practical implications for telecommunications, human health, and global ecosystems. A recent proposition that the present rate of dipole decay is driven by the South Atlantic anomaly and is only a few hundred years old suggests that long-term changes could result from a series of transient centennial scale features, which are difficult to resolve in the short historical record. Understanding the interplay between transient and persistent geomagnetic features over longer time intervals in the paleomagnetic record is, therefore, likely to play a significant role in deciphering the dynamics of the geodynamo, as well as having implications for mechanisms of long-term production of cosmogenic isotopes in the atmosphere, which have been used to infer solar variability and its impact on past climate changes. Recent paleomagnetic observations are now beginning to document transient features as abrupt sub-millennial and even sub-centennial paleomagnetic field behaviors. Paleomagnetic secular variation (PSV) records that record abrupt features are so-far limited to the Atlantic hemisphere (eastern North America, Iceland/Greenland, Europe/Middle East). Whether this reflects asymmetry of the field or a lack of available data is presently unclear. This project will test the spatial scale of abrupt geomagnetic behavior and beginning to assess PSV of the Pacific, while providing high quality data for the next generation of spherical harmonic models, through a detailed study of sediments from the Southeast Alaska continental margin. This opportunity arises because of recently collected new jumbo piston cores of extraordinarily high sedimentation rate (meters to 10's of meters per thousand years) with favorable magnetic properties, on cruse EW0408 of R/V Ewing. Paleomagnetic secular variation will be studied on eight out of 27 available jumbo piston cores using u-channel and discrete sample methods. Biogenic components suitable for radiocarbon dating are present, although severely diluted by the terrigenous sediment. Detailed chronologies based on radiocarbon will be developed using new techniques of precise accelerator 14C dating of ultra-small samples, developed at the Keck AMS Laboratory at UC Irvine. This study will, therefore, fill a significant data gap, test hypotheses on magnetic field variability and employing new methods for both high-resolution paleomagnetic measurements and fine-scale chronologic constraints that will substantially advance understanding of the dynamics of Earth's magnetic field. The data generated will contribute to differentiating the timescales of geomagnetic versus solar control on terrestrial cosmic ray flux and cosmogenic isotope production. This is significant for understanding both climatic and solar variability, and important to society because the magnetic field shields the earth from cosmic ray bombardment, with practical implications for telecommunications, human health, and global ecosystems. Regional PSV and relative paleointensity master curves will be developed and used as stratigraphic templates for a variety of marine and terrestrial paleoclimatic studies. Data will be contributed to databases and used to supplement ongoing spherical harmonic studies of the field from a region with little data. Radiocarbon results will contribute to understanding of changing reservoir ages in the North Pacific region, of interest to improving chronologies of past climate changes, and to understanding variations in the oceans carbon cycle. This project will support the training of both undergraduate honors students and graduate students.

对历史地磁领域的观察及其从多种来源的安全变化揭示了短暂和持续的地磁特征。持续的特征包括太平洋相对于大西洋半球的柔和的安全变化，以及在约60°N latitude的加拿大和西伯利亚的集中地磁通量区域。瞬态历史特征包括北磁极的运动和南大西洋下方的核/地幔边界上不断增长的反向磁通量区域。除了目前的偶极强度衰减率为每一世纪的5％（自由衰减率的五倍）之外，这些观察结果使一些研究人员推测地磁场可能正朝着反向或游览朝向。最近加速的偶极衰减是否可能继续进行的问题对社会很重要，因为磁场使地球免受宇宙射线轰炸，对电信，人类健康和全球生态系统产生了实际影响。最近的提议是，偶极衰减的目前速率是由南大西洋异常驱动的，并且只有几百年的历史表明，长期变化可能是由于一系列短暂的百年尺度特征造成的，这在短期历史记录中很难解决。因此，了解古磁记录中较长时间间隔的瞬态与持续的地磁特征之间的相互作用可能在解释地毛的动力学方面发挥重要作用，并且对长期产生的大气中的共同基质产生的机制具有影响，这些机制是在大气中使用次数变化及其对次数变化的大气的影响。最近的古磁观测现在开始记录瞬时特征，例如突然的亚千禧一代，甚至亚元素次年古磁场行为。古磁性安全变化（PSV）记录，记录突然的特征仅限于大西洋半球（北美东部，冰岛/格陵兰，欧洲/中东）。这是不清楚的是反映现场的不对称性还是缺乏可用数据。该项目将测试突然地磁行为的空间尺度，并开始评估太平洋的PSV，同时通过对阿拉斯加东南部连续边缘的沉积物进行详细研究，为下一代球形谐波模型提供高质量的数据。这一机会之所以出现，是因为最近收集的新型巨型活塞核心具有高度高的沉积速率（每千年米至10米），并具有有利的磁性特性，该磁性具有良好的磁性性能，该磁性在r/v ewing的Cruse EW0408上。使用U通道和离散的样本方法，将在27个可用的巨型活塞核中的8个中的8个可用的巨型活塞芯上进行研究。存在适用于放射性碳年代的生物成分，尽管被陆质沉积物严重稀释。基于放射性碳的详细时间顺序将使用在UC Irvine的Keck AMS实验室开发的Precision Accelerator 14C约会的新技术。因此，这项研究将填补大量的数据差距，检验磁场可变性的假设，并采用新方法来实现高分辨率古磁测量和精细规模的按时间顺序结构的约束，从而实质上提高了对地球磁场动力学的理解。产生的数据将有助于区分地磁与太阳能控制的时间尺度对地面宇宙射线通量和宇宙同位素的产生。这对于理解气候变化和太阳可变性非常重要，并且对社会很重要，因为磁场使地球免受宇宙射线轰炸，对电信，人类健康和全球生态系统产生了实际影响。将开发区域PSV和相对古显着的主曲线，并用作各种海洋和陆地古气候研究的地层模板。数据将有助于数据库，并用于补充几乎没有数据的区域对现场的持续球形谐波研究。放射性碳的结果将有助于理解北太平洋地区变化的参与者年龄，以改善过去气候变化的时间顺序，并了解海洋碳循环的变化。该项目将支持对本科生的培训，以纪念学生和研究生。