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以及地球发电机模拟研究强调了非轴对称通量集中的重要性，不仅作为地幔对地球发电机具有重要影响的指标，而且还表明它可能充当潜在的组织结构，控制地磁场的大部分动态，包括古地磁长期变化（PSV）。对关键位置的特定的、已确定日期的全新世 PSV 倾角、偏角和古强度时间序列的比较表明，存在一个相对简单的一阶模式，该模式在过去四千年的最高质量数据可用的情况下被最清楚地观察到。在这个时间范围内，场形态可以大致分为两种“模式”：第一种模式在北美上空具有主导通量波瓣，第二种模式在欧洲上空具有主导通量波瓣。 “北美模式”与历史时间平均场一致。 “欧洲模式”与全新世中晚期场的时间平均一致。根据阿拉斯加以及较早的夏威夷和俄勒冈记录对东北太平洋地区进行的新的倾斜异常重建表明，这种振荡的影响可能会延伸到太平洋，并持续到全新世甚至更久。这种振荡的发现将是了解 PSV 驱动因素的重要一步。不幸的是，由于年代学的不确定性和现代相对古强度记录的有限，来自北美和东北太平洋的现有 PSV 数据不足以充分评估观察到的关系是否在较长的古地磁时间间隔内持续存在。这项为期三年的研究将重点关注北美和东北太平洋记录，以改善观测约束并评估数据导出的 PSV 时间序列与连续球谐模型之间的关系，从而为 PSV 记录的解释提供信息。数据质量（包括年代学）是我们理解 PSV 地磁原因的限制因素。这将通过综合现有数据和放射性碳测年，以及从经典古地磁遗址和其他附近具有经过证实的沉积记录但尚未采用现代测年和古地磁实践的地点收集新的岩心来改进。记录的原因有很多，其中最根本的是了解地球磁场过去的历史。对岩石、沉积物和考古文物进行的古地磁观测提供了有关地磁场产生过程的基本信息，而这些信息是无法从短暂的历史记录中获得的。这些观测结果告诉我们，地磁方向和强度的大幅度变化会在数十年到数百万年的时间尺度内发生。 然而，我们对控制古地磁变化的过程和边界条件的了解还很不完整，导致我们对地磁场和受地磁变化控制的任何过程（从磁地层学到空间气候）的理解存在很大的不确定性。 这项研究旨在确定边界条件是否可以作为一种潜在的组织结构，控制地磁场的大部分动态，包括被称为古地磁长期变化（PSV）的千年和百年尺度变化。研究结果将有助于区分地磁和太阳强迫对地球宇宙线通量和宇宙同位素产生的贡献，对电信、人类健康、全球生态系统和气候具有实际意义。气候变化与田地形态之间的潜在联系是一个相对较新的研究课题，在气候快速变化的时期值得特别关注。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的了解程度的限制。了解古地磁变化的地磁原因将为磁地层学提供重要的新机会。该项目将支持本科生、研究生和博士后教育，提供岩心收集、地层学、古磁数据分析、环境磁数据分析、地磁、地质年代学和古气候学方面的培训。