Collaborative Research: Towards an understanding of the Holocene paleomagnetic record through new data (Hawaii/North American) and time series/spherical harmonic model comparisons

合作研究：通过新数据（夏威夷/北美）和时间序列/球谐模型比较来了解全新世古地磁记录

• 批准号: 1215661
• 负责人: Mark Abbott
• 金额: $ 24.66万
• 依托单位: University of Pittsburgh
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2012
• 资助国家: 美国
• 起止时间: 2012-08-01 至 2015-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1215661&HistoricalAwards=false
• 关键词: Collaborative; Research; Towards; understanding; Holocene

Historical and recent paleomagnetic observations, along with geodynamo modeling studies highlight the importance of non-axisymmetric flux concentrations, not only as an indicator that the mantle has an important influence on the geodynamo, but also that it may act as a potential organizing structure that might control much of the dynamics of the geomagnetic field including paleomagnetic secular variation (PSV). Comparison of specific, well-dated Holocene PSV time series of inclination, declination, and paleointensity at key locations suggest the existence of a relatively simple first order pattern that is most clearly observed over the last four thousand years where the highest quality data are available. Over this time range, the field morphology can be roughly broken into two "modes": The first mode having a dominant flux lobe over North America and the second a dominant flux lobe over Europe. The "North American mode" is consistent with the historically time averaged field. The "European mode" is consistent with the time averaged mid-to-late Holocene field. A new inclination anomaly reconstruction for the NE Pacific region derived from Alaskan, and older Hawaiian and Oregon records, suggests that the influence of this oscillation may extend into the Pacific and continue through the Holocene and possibly beyond. The discovery of such an oscillation would be a significant step toward an understanding of what drives PSV. Unfortunately, available PSV data from North America and the northeast Pacific, because of uncertain chronologies and limited modern relative paleointensity records, are not adequate to fully assess whether the relationship observed persists over longer paleomagnetic time intervals. This three-year study will focus on the North American and northeast Pacific records to improve observational constraints and assess the relationship between data derived PSV time series and continuous spherical harmonic models to inform the interpretation of the PSV record. Data quality, including chronology is a limiting factor in our understanding of the geomagnetic causes of PSV. This will be improved through a synthesis of existing data and radiocarbon dates, and the collection of new cores from classic paleomagnetic sites and other nearby locations with proven sedimentary records, but where modern dating and paleomagnetic practices have yet to be employed.We study the paleomagnetic record for many reasons, with the most fundamental being to understand the past history of Earth's magnetic field. Paleo-geomagnetic observations from rocks, sediments, and archeological artifacts provide fundamental information about geomagnetic field generation process that cannot be obtained from the short historical record. These observations tell us that large amplitude geomagnetic changes in direction and intensity occur over timescales that range from decades to millions of years. Yet our knowledge of the processes and boundary conditions that govern paleo-geomagnetic change are far from complete resulting in significant uncertainty in our understanding of the geomagnetic field and any process controlled by geomagnetic change, from magnetic stratigraphy to space climate. This study is designed to determine if boundary conditions may act as a potential organizing structure that might control much of the dynamics of the geomagnetic field including millennial and centennial scale changes know as paleomagnetic secular variation (PSV). Results will help to differentiate between the contributions of geomagnetic and solar forcing of terrestrial cosmic ray flux and cosmogenic isotope production with practical implications for telecommunications, human health, global ecosystems and climate. The potential linkage between climate change and field morphology is a relatively new topic of research and one that deserves special attention at this time of rapid climate change. Holocene magnetic stratigraphy has a long history, but its usefulness is ultimately limited by how well we know the paleomagnetic record. An understanding of the geomagnetic cause of paleomagnetic change will provide significant new magnetic stratigraphic opportunities. This project will support undergraduate, graduate, and postdoctoral education, providing training in core collection, stratigraphy, paleomagnetic data analysis, environmental magnetic data analysis, geomagnetism, geochronology and paleoclimatology.

历史和最近的古地磁观测，沿着与地球发电机建模研究突出了非轴对称通量集中的重要性，不仅作为一个指标，地幔有一个重要的影响地球发电机，但它也可能作为一个潜在的组织结构，可能会控制大部分的地磁场的动态，包括古地磁长期变化（PSV）。特定的，以及过时的全新世PSV时间序列的倾斜度，下降，和paleointensity在关键位置的比较表明，存在一个相对简单的一阶模式，是最清楚地观察到在过去的四千年中，最高质量的数据。在这个时间范围内，场形态可以大致分为两个“模式”：第一个模式在北美有一个主导的通量波瓣，第二个模式在欧洲有一个主导的通量波瓣。“北美模式”与历史上的时间平均场是一致的。“欧洲模式”是一致的时间平均的中晚全新世领域。一个新的倾角异常重建东北太平洋地区来自阿拉斯加，和更老的夏威夷和俄勒冈州记录，表明这种振荡的影响可能会延伸到太平洋，并继续通过全新世和可能超越。这种振荡的发现将是理解PSV驱动因素的重要一步。不幸的是，现有的PSV数据从北美和太平洋东北部，因为不确定的年表和有限的现代相对paleointensity记录，不足以充分评估是否观察到的关系持续较长的古地磁时间间隔。这项为期三年的研究将侧重于北美和东北太平洋的记录，以改善观测约束，并评估PSV时间序列和连续球谐模型数据之间的关系，为PSV记录的解释提供信息。数据质量，包括年表是我们理解PSV的地磁原因的一个限制因素。通过综合现有的数据和放射性碳年代测定，以及从经典古地磁遗址和附近其他有沉积记录的地点收集新的岩心，但现代年代测定和古地磁实践尚未被采用，这将得到改善。我们研究古地磁记录的原因有很多，最根本的是了解地球磁场的过去历史。来自岩石、沉积物和考古文物的古地磁观测提供了从短暂的历史记录中无法获得的关于地磁场生成过程的基本信息。这些观测告诉我们，地磁方向和强度的大幅变化发生在几十年到几百万年的时间尺度上。 然而，我们对古地磁变化的过程和边界条件的了解还远远不够，导致我们对地磁场和地磁变化控制的任何过程（从磁性地层学到空间气候）的理解存在很大的不确定性。 这项研究的目的是确定边界条件是否可以作为一个潜在的组织结构，可能会控制地磁场的大部分动态，包括千年和百年尺度的变化，称为古地磁长期变化（PSV）。研究结果将有助于区分地磁和太阳对地球宇宙射线通量的作用力和宇宙成因同位素的产生，并对电信、人类健康、全球生态系统和气候产生实际影响。气候变化和田间形态之间的潜在联系是一个相对较新的研究课题，在气候迅速变化的今天值得特别关注。全新世磁性地层学有着悠久的历史，但它的实用性最终受到我们对古地磁记录了解程度的限制。对古地磁变化的地磁成因的认识将为磁性地层学研究提供新的机遇。该项目将支持本科生、研究生和博士后教育，提供岩心采集、地层学、古地磁数据分析、环境磁力数据分析、地磁学、地质年代学和古气候学方面的培训。