Developing a high-resolution Holocene paleo-geomagnetic reconstruction from northern North Atlantic sediments to place the historical geomagnetic field in perspective

从北大西洋北部沉积物中进行高分辨率全新世古地磁重建，以透视历史地磁场

• 批准号: 1645411
• 负责人: Joseph Stoner
• 金额: $ 25万
• 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: 2017
• 资助国家: 美国
• 起止时间: 2017-08-01 至 2021-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1645411&HistoricalAwards=false
• 关键词: Developing; resolution; Holocene; paleo; geomagnetic

In contrast with the geomagnetic field during historical times, the geomagnetic field during prehistoric (paleo) times is poorly described. As a result it is difficult to know the context in which to place the historical record of the geomagnetic field including features that have changed and those that have persisted. Some researchers have considered historical times to be anomalous, but if so, how anomalous? Should we be concerned about what future changes may bring or are historical behaviors that have gained attention just part of normal background variability. With better data and data analysis approaches our understanding of the prehistoric (paleo)-geomagnetic field has improved substantially over the last decade. Scientists are beginning to define paleo-geomagnetic dynamics that happen on thousands of years. But we do not know how these changes relate to historical type variations or whether the rates of change of the geomagnetic field are consistent or uneven. This project will address this through a reconstruction of the paleo-geomagnetic record of the northern North Atlantic from ultrahigh accumulating sediments that allow paleo-geomagnetic records to be developed at sub-centennial resolution through the last 10,000 years. The northern North Atlantic is an optimal location because it is a region of extreme geomagnetic sensitivity and one where high quality paleo records with little smoothing can be obtained. The latter is important as most sedimentary records smooth over historically relevant time intervals providing little context. The investigators will scrutinize present records in detail and combine them with new ultrahigh resolution records to provide high quality records with well-constrained uncertainties. This will provide fundamental observations on paleo-geomagnetic changes from a strategic location and of a quality where the interactions between millennial and shorter changes can be evaluated, and as a result, allow the investigators to place modern changes into firmer prehistoric constraints. Additionally, this project will provide an interpretive framework to more completely understand the processes deep within Earth that drive the geomagnetic field and how the geomagnetic shield that protects us from cosmic rays and solar winds varies through time and is likely to do so again; with practical implications for telecommunications, human health, and global ecosystems. Regional stratigraphic master dating curves will be refined. This project will support postdoctoral education continuing an investment in those that we have trained to make sure our initial investment does not fail. Data will be contributed to national databases and used to supplement ongoing big data studies of the geomagnetic field with well-characterized data. Exhibits and presentations on the theme What mud can tell us about Earth's magnetic field will be developed in collaboration with the OSU Marine Geology Repository and delivered to K-12, undergraduate, and adult learner through tours and classes and through the CEOAS booth at the Corvallis Saturday Market.The geomagnetic field is changing; the question is what sort of change is taking place. Some have speculated that a polarity reversal is imminent; others have suggested that such a change, if happening at all, is thousands of years away at the soonest. Much of the ambiguity results from a lack of paleo-context from which to place the historical geomagnetic field. Even though the paleo-record is poorly constrained relative to historical, our understanding of this record is improving and suggests that we are undergoing the latest of a series of millennial scale changes of the field that describe the Holocene, but what happens on shorter timescale analogous to the historical record is essentially unknown. The change that is happening at present is just one example, but whether this is large or small or unique or normal is not known. This project will provide observational constraints on paleo-geomagnetic change from a strategic location and of a quality where the interactions between millennial/centennial and geomagnetic changes on shorter time scales can be evaluated. As a result these observations will provide a paleo-context from which to evaluate historical geomagnetic change. To do this the team will use records from the northern North Atlantic, a location of fundamental paleomagnetic importance for three essential reasons. First, the structure of the modern geomagnetic field, changes observed historically, and paleomagnetic records all point to the northern North Atlantic as a region sensitive to changes in the geomagnetic field's morphology. Second, aggressive glacial erosion of strongly magnetic bedrock, along with a vigorous redistribution system results in paleomagnetic record of high fidelity often accumulating at high rates in both marine and terrestrial (lake) settings. Third, high carbonate production and preservation in marine environments allow for detailed radiocarbon chronologies, while numerous tephra layers enable reservoir ages to be assessed resulting in well constrained chronologies. Exceptional paleo-geomagnetic records that result are capable of uncovering many aspect of the geomagnetic field with unprecedented accuracy and resolution through the Holocene. The present set of records are enlightening; unveiling features never before seen, but are far from perfect, with notable gaps over the last few thousand years, occasional discrepancies between overlapping records (especially with relative paleointensity), and have not been adequately synthesized. Significant improvements are still possible, as concerted efforts to constrain the regions paleoclimatic record have resulted in a large number of sediment cores on and around Iceland/Greenland that retain suitable properties for high fidelity paleomagnetic records. Many of these records have already been dated and some have associated paleomagnetic data (often incompletely assessed) already in place. The investigators will take advantage of these sediment archives and data to support development of a sub-centennial resolution paleo-geomagnetic reconstructions from the northern North Atlantic that overlaps with the historical record and continues through the Holocene with enough observations to constrain and reduce uncertainties in both chronology and paleomagnetic measurables. This paleo-geomagnetic synthesis will provide an interpretive framework to more completely assess past variations required to further our understanding of the geodynamo process controlling the geomagnetic field and the geomagnetic shield and its control on the production of cosmic nuclides; a hinge point for our understanding of processes ranging from solar variability to climate with practical implications for telecommunications, human health, and global ecosystems. Regional stratigraphic master dating curves will be refined. Data will be contributed to national databases (MagIC, NOAA ) providing well constrained data for ongoing spherical harmonic analyses of the geomagnetic field. Exhibits and presentations on the theme "What mud can tell us about Earth's magnetic field" will be developed in collaboration with the OSU Marine Geology Repository and delivered to K-12, undergraduate, and adult learner through tours and classes and through the CEOAS booth at the Corvallis Saturday Market.

与历史时期的地磁场相比，史前（古）时期的地磁场描述得很少。因此，很难知道放置地磁场历史记录的背景，包括那些已经改变的特征和那些持续存在的特征。一些研究人员认为历史时间是反常的，但如果是这样，反常的程度如何？我们是否应该担心未来的变化会带来什么，或者已经引起注意的历史行为只是正常背景变化的一部分。有了更好的数据和数据分析方法，我们对史前（古）地磁场的理解在过去十年中有了很大的提高。科学家们开始定义几千年后发生的古地磁动力学。但是我们不知道这些变化与历史类型的变化有什么关系，也不知道地磁场的变化率是一致的还是不均匀的。该项目将通过重建北大西洋北部超高积累沉积物的古地磁记录来解决这个问题，这使得古地磁记录能够在过去1万年的次百年分辨率下得到发展。北大西洋北部是一个最理想的位置，因为它是一个地磁极端敏感的地区，在那里可以获得高质量的古记录，几乎没有平滑。后者很重要，因为大多数沉积记录在与历史相关的时间间隔上很平滑，提供的背景很少。调查人员将详细审查现有记录，并将其与新的超高分辨率记录相结合，以提供具有良好约束不确定度的高质量记录。这将从战略位置和质量上提供古地磁变化的基本观测，从而可以评估千年和较短变化之间的相互作用，从而使研究人员能够将现代变化置于更牢固的史前约束中。此外，该项目将提供一个解释性框架，以更全面地了解地球深处驱动地磁场的过程，以及保护我们免受宇宙射线和太阳风影响的地磁屏蔽如何随时间而变化，并可能再次发生变化；对电信、人类健康和全球生态系统具有实际影响。完善区域地层主控测年曲线。这个项目将支持博士后教育，继续对我们培养的博士后进行投资，以确保我们的初始投资不会失败。数据将提供给国家数据库，并用于补充正在进行的具有良好特征的地磁场大数据研究。关于泥浆能告诉我们地球磁场的主题的展览和演讲将与俄勒冈州立大学海洋地质储库合作开发，并通过参观和课程以及在科瓦利斯星期六市场的CEOAS展位向K-12，本科生和成人学习者提供。地磁场在变化；问题是正在发生什么样的变化。一些人推测极性反转即将来临；其他人则认为，这样的变化，如果真的发生的话，最快也要几千年以后。许多模棱两可的结果是由于缺乏古环境来确定历史上的地磁场。尽管古记录相对于历史记录的约束很差，但我们对这一记录的理解正在改善，并表明我们正在经历一系列描述全新世的千年尺度变化的最新阶段，但类似于历史记录的更短时间尺度上发生的变化基本上是未知的。目前正在发生的变化只是一个例子，但这种变化是大还是小，是独特的还是正常的还不得而知。该项目将从战略位置和质量上提供古地磁变化的观测约束，从而可以在较短的时间尺度上评估千年/百年地磁变化之间的相互作用。因此，这些观测结果将为评估历史地磁变化提供一个古背景。为了做到这一点，研究小组将使用北大西洋北部的记录，因为三个基本原因，北大西洋北部是古地磁的重要位置。首先，现代地磁场的结构、历史上观测到的变化和古地磁记录都表明北大西洋北部是一个对地磁场形态变化敏感的地区。其次，强磁性基岩的剧烈冰川侵蚀，加上强有力的再分配系统，导致高保真度的古地磁记录经常在海洋和陆地（湖泊）环境中以高速率积累。第三，海洋环境中的高碳酸盐产量和保存使得可以进行详细的放射性碳年代学，而大量的热层可以评估储层的年龄，从而得到良好的年代学约束。独特的古地磁记录能够以前所未有的精度和分辨率揭示全新世地磁场的许多方面。目前的记录很有启发性；揭示了以前从未见过的特征，但远非完美，在过去的几千年里有明显的差距，重叠记录之间偶尔存在差异（特别是相对古强度），并且没有得到充分的综合。由于限制区域古气候记录的共同努力，冰岛/格陵兰岛及其周围的大量沉积物岩心保留了适合高保真古地磁记录的特性，因此仍有可能取得重大改进。这些记录中的许多已经确定了年代，有些已经有了相关的古地磁数据（通常评估不完全）。研究人员将利用这些沉积物档案和数据来支持北大西洋北部亚百年分辨率古地磁重建的发展，该重建与历史记录重叠，并持续到全新世，通过足够的观测来限制和减少年代学和古地磁测量的不确定性。这种古地磁综合将提供一个解释框架，以更完整地评估过去的变化，从而进一步了解控制地磁场和地磁屏蔽的地球动力过程及其对宇宙核素产生的控制；这是我们理解从太阳变率到气候等过程的关键，对电信、人类健康和全球生态系统具有实际意义。完善区域地层主控测年曲线。数据将提供给国家数据库（MagIC， NOAA），为正在进行的地磁场球谐分析提供约束良好的数据。主题为“泥浆能告诉我们关于地球磁场的什么”的展览和演讲将与俄勒冈州立大学海洋地质储库合作开发，并通过参观和课程以及在科瓦利斯星期六市场的CEOAS展位向K-12，本科生和成人学习者提供。

项目成果

Dynamic time warping of palaeomagnetic secular variation data

古地磁长期变化数据的动态时间扭曲

• DOI: 10.1093/gji/ggaa004
• 发表时间: 2020
• 期刊: Geophysical Journal International
• 影响因子: 2.8
• 作者: Hagen, Cedric J;Reilly, Brendan T;Stoner, Joseph S;Creveling, Jessica R
• 通讯作者: Creveling, Jessica R