Reanalysis of Paleomagnetic Secular Variation and Excursions During Early Brunhes Time (380-780 ka) at ODP Sites 1060, 1061, 1062, and 1063

ODP 站点 1060、1061、1062 和 1063 早期 Brunhes 时间（380-780 ka）古地磁长期变化和偏移的再分析

• 批准号: 2219330
• 负责人: Steven Lund
• 金额: $ 16.36万
• 依托单位: University of Southern California
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2022
• 资助国家: 美国
• 起止时间: 2022-09-01 至 2024-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2219330&HistoricalAwards=false
• 关键词: Reanalysis; Paleomagnetic; Secular; Variation; Excursions

This project will develop high-resolution paleomagnetic secular variation (PSV) records of the Earth’s magnetic field in the region of the western North Atlantic Ocean for the time interval 380,00-780,000 years ago. These composite PSV records will contain records of directional variability, including evidence for 6 magnetic field excursions, and intensity variability. A similar analysis is now complete for the last 380,000 years containing 12 excursions. In combination, these PSV records will provide evidence for the behavior of the Earth’s dynamo for the last 780,000 years (Brunhes Normal Polarity Chron) that is unique in the World. These records should provide the evidence needed to determine what happens when the Earth’s magnetic field reverses. There are many records of field reversals, but none of them have a detailed record of field variability surrounding the actual reversal. This work should provide a unique set of PSV records for evaluating the magnetic field reversal dynamo process. These records will provide, as well, the pattern of PSV variability throughout the Brunhes Chron that can help to characterize the normal chaotic pattern of the Earth’s dynamo active in the outer core. The project will support undergraduate student research.Ocean Drilling Program (ODP) Leg 172 (western North Atlantic Ocean) collected shipboard paleomagnetic records (2-3 holes per site) from Sites 1060, 1061 1062, and 1063 for the entire Brunhes Normal Polarity. The sampling interval at these sites was 5 cm with an average sediment accumulation rate of ~25 cm/ky (200-yr average sampling interval). These composite data sets contain, perhaps, the highest-resolution record of paleomagnetic field variability (directions, relative paleointensity, excursions) for the entire Brunhes Normal Polarity Chron anywhere in the World. This project will carry out a reanalysis of excursions and surrounding normal secular variation (both directions and relative paleointensity) recorded in these deep-sea sediments between 380-780 ka. Lund (2018) and Lund et al. (2020a, 2020b, 2021, 2022) have already carried out such a reanalysis and constructed a composite paleomagnetic record for each of these sites from 0-380 ka. This reanalysis will build detailed replicate PSV records for each of the sites and reevaluate the chronologies for them. Time series analysis will be used to assess the pattern of variability over time and its relationship to the intervening 18 excursions. For the first time, the relationship between normal PSV surrounding the excursions will be evaluated as a model for reversal process. This project will also provide a basis for estimating the detailed space/time pattern of excursions/secular variation in one region that can be compared with other, similar studies from other parts of the Earth. These analyses are are key concepts for building more realistic models of dynamo sources for excursions and normal secular variation in the outer core.This project is supported by the Marine Geology and Geophysics program in the Division of Ocean Sciences and the Geophysics program in the Division of Earth Sciences.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

该项目将制作北大西洋西部地区380 000 - 780 000年前地球磁场的高分辨率古地磁长期变化记录。这些复合PSV记录将包含方向变化记录，包括6个磁场偏移和强度变化的证据。一个类似的分析现在已经完成了过去38万年，包含12次偏移。结合起来，这些PSV记录将为过去78万年来地球发电机的行为提供证据（Brunhes正常极性Chron），这在世界上是独一无二的。这些记录应该提供了必要的证据，以确定当地球磁场逆转时会发生什么。有许多关于磁场反转的记录，但没有一个详细记录了围绕实际反转的磁场变化。这项工作应提供一套独特的PSV记录，用于评估磁场反转发电机过程。这些记录将提供，以及，整个Brunhes年代的PSV变化的模式，可以帮助描述正常的混沌模式的地球的发电机活跃在外核。该项目将支持本科生的研究。大洋钻探计划（ODP）172航次（北大西洋西部）收集了船上的古地磁记录（每个站点2-3个孔）从站点1060，1061，1062和1063为整个布鲁赫正常极性。这些地点的采样间隔为5厘米，平均沉积物累积率约为25厘米/千公里（200年平均采样间隔）。这些复合数据集包含，也许，最高分辨率的记录古磁场的变化（方向，相对paleointensity，偏移）为整个Brunhes正常极性Chron在世界任何地方。该项目将对380-780 ka期间记录在这些深海沉积物中的偏移和周围正常长期变化（两个方向和相对古强度）进行重新分析。隆德（2018）和隆德等人（2020 a，2020 b，2021，2022）已经进行了这样的再分析，并为这些地点构建了0-380 ka的复合古地磁记录。该重新分析将为每个研究中心建立详细的重复PSV记录，并重新评估它们的年表。将使用时间序列分析评估随时间变化的模式及其与干预18次波动的关系。第一次，围绕偏移的正常PSV之间的关系将作为逆转过程的模型进行评估。该项目还将提供一个基础，用于估计一个区域的漂移/长期变化的详细空间/时间模式，以便与地球其他地区的其他类似研究进行比较。这些分析是建立更真实的外核漂移和正常长期变化的发电机源模型的关键概念。该项目由海洋科学部的海洋地质学和地球物理学计划以及地球科学部的地球物理学计划支持。该奖项反映了NSF的法定使命，并通过使用基金会的智力价值进行评估而被认为值得支持和更广泛的影响审查标准。