Collaborative Research: High temporal resolution paleomagnetism of speleothems

合作研究：洞穴生物的高时间分辨率古地磁学

• 批准号: 2044806
• 负责人: Eduardo Andrade Lima
• 金额: $ 33.02万
• 依托单位: Massachusetts Institute of Technology
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2021
• 资助国家: 美国
• 起止时间: 2021-04-15 至 2025-03-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2044806&HistoricalAwards=false
• 关键词: Collaborative; Research; temporal; resolution; paleomagnetism

Speleothems (stalagmites, stalactites, flowstone) are cave mineral deposits that form by dripping, flowing, and seeping water containing dissolved elements from the overlying bedrock. Speleothem growth may span tens of thousands of years and provide a natural archive of climatic and environmental conditions during that period. Usually, they also include minute concentrations of magnetic minerals from overlying soils, which could ultimately provide a continuous record of Earth’s magnetic field during that time interval. Precise dating of speleothems has opened up the possibility of accessing invaluable information from those magnetic records about past episodes of short-duration geomagnetic instability (for example, rapid changes in the strength or direction of Earth’s magnetic field). In turn, these instabilities may reveal critical information about the mechanism by which Earth’s magnetic field is generated (known as the geodynamo), advance investigations of possible links between geomagnetic and climatic events, and provide important data about how fluctuations in the Earth’s magnetic field strength may affect the performance of satellite communications. Retrieval of high-resolution magnetic records from speleothems has been challenging until now owing to the very weak magnetization they carry. However, latest developments in state-of-the-art magnetometry technologies and dating techniques have made it possible to conduct high-resolution analysis of past magnetic fields in recent geological history. This research project will enable outreach activities at the Smithsonian National Museum of Natural History, support a postdoctoral researcher and part-time participation of a graduate student, provide support for an undergraduate internship targeting underrepresented minorities in STEM, facilitate undergraduate research projects, and provide hands-on experience in speleothem magnetism for twenty beginning graduate students from around the globe as part of a summer school on rock magnetism.This project focuses on using speleothems, which lock in magnetizations on sub-annual timescales, to study the Laschamp geomagnetic excursion (~41 ka), one of the most important geomagnetic instabilities in the geologic record. Time-synchronous observations from the mid-latitudes of the northern hemisphere (Missouri, US) and the low-latitudes of the southern hemisphere (Bahia and Minas Gerais, Brazil) will provide well-dated, high-resolution paleomagnetic records that fill critical gaps in the most recent spherical harmonic models and allow examination of a time period thought to display some of the fastest geomagnetic changes of the last 100,000 years. High spatial and temporal resolutions (1-10 years) will be achieved by leveraging the continuous paleomagnetic recordings preserved in speleothems through a combination of techniques, including superconducting quantum interference device (SQUID) microscopy, quantum diamond microscopy (QDM), scanning electron microscopy (SEM) tomography, and transmission electron microscopy (TEM). Specific goals include (1) studying short-term geomagnetic behavior using oriented speleothems known to have grown across the Laschamp excursion collected from Brazil and the United States; (2) investigating the fine-scale processes controlling acquisition of remanence in speleothems and assessing the robustness of the magnetic record obtained from such cave formations; and (3) further developing the workflow for scanning magnetometry to confidently recover full-vector records from speleothems that take maximum advantage of their annual layering. These paleomagnetic data will represent some of the highest resolution, most robustly dated records across the Laschamp excursion. They will improve the geographic coverage and geochronological rigor of future spherical harmonic models and contribute to a deeper understanding of geodynamo instability. Additionally, advanced SEM tomography and TEM-based mineralogic analyses will provide an in situ view of a subset of the magnetic minerals that retain the paleomagnetic recording in these materials, helping address unresolved questions related to the acquisition of remanence.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.

洞穴沉积物（石笋，钟乳石，流石）是洞穴矿物沉积物，由含有溶解元素的水从上覆基岩滴落，流动和渗透而形成。洞穴沉积物的生长可能跨越数万年，并提供了这一时期气候和环境条件的自然档案。通常，它们还包括来自覆盖土壤的磁性矿物的微小浓度，这最终可以提供该时间间隔内地球磁场的连续记录。洞穴沉积物的精确年代测定使人们有可能从这些磁记录中获取有关过去短时间地磁不稳定事件（例如，地球磁场强度或方向的快速变化）的宝贵信息。反过来，这些不稳定性可能揭示关于地球磁场产生机制（称为地球发电机）的关键信息，推进对地磁和气候事件之间可能联系的调查，并提供关于地球磁场强度波动如何影响卫星通信性能的重要数据。从洞穴沉积物中提取高分辨率的磁性记录一直是一个挑战，直到现在，由于它们携带的非常弱的磁化。然而，最先进的磁力测量技术和测年技术的最新发展使得有可能对近代地质历史中过去的磁场进行高分辨率分析。该研究项目将在史密森尼国家自然历史博物馆开展外联活动，支持博士后研究员和研究生的兼职参与，为针对STEM中代表性不足的少数民族的本科生实习提供支持，促进本科生研究项目，提供人手作为岩石磁学暑期班的一部分，为来自地球仪的20名研究生提供洞穴磁学方面的经验。利用洞穴沉积物，锁定在次年度时间尺度上的磁化，研究Laschamp地磁漂移（~41 ka），这是地质记录中最重要的地磁不稳定性之一。来自北方半球中纬度地区（美国密苏里州）和南半球低纬度地区（巴西的巴伊亚和米纳斯吉拉斯）的时间同步观测将提供日期准确、高分辨率的古地磁记录，填补了最新球谐模型中的关键空白，并允许检查被认为显示过去10万年来地磁变化最快的时间段。高空间和时间分辨率（1-10年）将通过利用保存在洞穴沉积物中的连续古地磁记录来实现，这些记录通过超导量子干涉仪（SQUID）显微镜，量子金刚石显微镜（QDM），扫描电子显微镜（SEM）断层扫描和透射电子显微镜（TEM）等技术的组合来实现。具体目标包括：（1）利用从巴西和美国收集的已知在Laschamp漂移期间生长的定向洞穴沉积物研究短期地磁行为;（2）调查控制洞穴沉积物中剩磁获取的精细尺度过程，并评估从此类洞穴地层获得的磁记录的可靠性;以及（3）进一步发展扫描磁力测量的工作流程，以确保从最大限度地利用其年度分层的洞穴沉积物中恢复全矢量记录。这些古地磁数据将代表一些最高分辨率，最稳健的日期记录整个Laschamp偏移。它们将改善未来球谐模型的地理覆盖范围和地质年代学的严谨性，并有助于更深入地了解地球发电机的不稳定性。此外，先进的SEM断层扫描和TEM矿物学分析将提供保留这些材料中的古地磁记录的磁性矿物子集的原位视图，帮助解决与获得剩磁相关的未解决问题。该奖项反映了NSF的法定使命，并被认为值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估来支持。

项目成果

Estimating the Net Magnetic Moment of Geological Samples From Planar Field Maps Using Multipoles

使用多极从平面场图中估计地质样本的净磁矩

• DOI: 10.1029/2022gc010724
• 发表时间: 2023
• 期刊: Geosystems
• 作者: Lima, Eduardo A.;Weiss, Benjamin P.;Borlina, Caue S.;Baratchart, Laurent;Hardin, Douglas P.
• 通讯作者: Hardin, Douglas P.