Developing paleomagnetic chronologies of, and paleogeomagnetic understanding from, IODP sites U1486 and U1489 in the western Pacific warm pool.

从数千年到数百万年的时间尺度上对地球磁场的观测对于理解地球发电机如何运作和保护地球免受有害的太阳辐射是很重要的。随着海洋沉积物在海底的积累，它们记录了周围的磁场，从而提供了过去地磁行为的重要记录。许多现有的高质量记录跨越了过去的2-3百万年，来自北大西洋的沉积物，这代表了一个狭窄的，甚至可能是独特的磁地理范围。为了恰当地表示全球场及其变率，需要全球其他区域同一时期的记录。综合海洋钻探计划（IODP） 363远征队前往西太平洋暖池，在印度洋和太平洋的9个赤道地点钻探，并回收了总计7公里的海洋沉积物岩心。初步测量表明，其中两个地点，U1486和U1489，包含高质量的磁记录，可以用来调查和了解过去1.25亿年（U1486）和5亿年（U1489）地球磁场的行为。该项目旨在测量这些沉积物的磁性，以开发和完善地球最近磁场行为的高分辨率记录，并将其与北大西洋记录进行比较。该项目还将开发最长的连续相对古地磁强度时间序列，可追溯到上新世早期（~ 500万年前）。此外，这些古地磁记录将为该地区相关的详细同位素和气候研究提供一个年代学框架。在更广泛的影响和推广方面，该项目将直接支持博士后作为主要研究者的培训和发展，并将使俄勒冈州立大学的本科生了解基本的研究方法和概念。将特别关注参与原创研究的本科生，为本科生开发项目“所有权”，以及招募多样化的研究人员团队。来自北大西洋相对高沉积速率海洋岩心的古地磁记录强有力地提供和定义了我们目前对古地磁长期变化和相对古强度（RPI）的理解。从该盆地内复制的记录表明，RPI变化具有全球表达，反映了偶极场强度的随机变化。这一假设可能是正确的，然而，它从未被明确地验证过，部分原因是缺乏来自全球不同地区的记录，这些记录具有与北大西洋相似的解析能力（即沉积速率）。我们将从U1486和U1489的两份档案中提取u通道样品，在厘米尺度上测量自然剩余磁化（NRM）、非滞后剩余磁化（ARM）和等温剩余磁化（IRM）的磁化率和退磁行为。我们将使用这些数据来生成特征残余方向，并生成长更新世和上新世时间框架内的RPI估计。U1486站点1.25 Myr赤道太平洋海相沉积记录的非轴向偶极子结构和区域非均质性证据的分辨率比现有记录和叠片高数倍，与北大西洋高质量记录更接近。U1489遗址包含一个5兆瓦的沉积记录，它将发展成为有史以来最长的连续RPI记录。初步资料表明，该地层具有较高的保真度，与该地点同时发育的d18O底栖有孔虫地层相结合，有可能成为上新世地磁场行为的类型记录。这一记录不仅将成为上新世磁地层调整的目标，而且还将为研究（亚）轨道变化到完整年代和时代的地磁场演化和组织提供信息。rpi辅助的年代学将用于U1486和U1489的中晚更新世记录（通过与现有全球层叠的相关性），然后可以与d18O记录同步调整，以开发可靠的年代学并建立强大的年代学框架，以直接促进IODP 363考察的科学目标。

Observations of Earth's magnetic field over timescales from thousands to millions of years are important for understanding how the geodynamo operates and shields the Earth from harmful incoming solar radiation. As ocean sediments accumulate on the seafloor they record the ambient magnetic field and thereby provide an important record of past geomagnetic behavior. Many of the existing high quality records that span the last 2-3 million years are from North Atlantic Ocean sediments, which represents a narrow, and maybe even unique, magneto-geographical range. To properly represent the global field and its variability requires records from other regions of the globe for the same time period. Integrated Ocean Drilling Program (IODP) Expedition 363 to the West Pacific Warm Pool drilled nine equatorial sites in the Indian and Pacific Oceans and recovered a total of 7km of ocean sediment core. Preliminary measurements suggest two of these sites, U1486 and U1489, contain high quality magnetic records that can be used to investigate and understand the behavior of Earth's magnetic field over the last 1.25 (U1486) and 5 (U1489) million years. This project seeks to measure the magnetism of these sediments to develop and refine high resolution records of Earth's recent magnetic field behavior and compare them to North Atlantic records. The project will also develop the longest continuous relative paleomagnetic intensity time-series to date back to the earliest Pliocene (~5 million years ago). In addition, these paleomagnetic records will provide a chronological framework for related detailed isotope and climate studies for the region. In terms of broader impacts and outreach, this project will directly support the training and development of a post-doc as the principal investigator and will expose undergraduate students from Oregon State University to basic research methods and concepts. There will be special attention placed on undergraduates being involved in original research, the development of project "ownership" for undergraduate students, and in recruiting a diverse team of researchers.Paleomagnetic records derived from relatively high sedimentation rate marine cores in the North Atlantic strongly inform and define our current understanding of paleomagnetic secular variation and relative paleointensity (RPI). Replication of records from within this basin argue for RPI variations that have a global expression and reflect stochastic variations in the intensity of the dipolar field. This assumption is likely true, however, it has never explicitly been tested, in part due to a lack of records from different regions of the globe that have a similar resolving ability (i.e. sedimentation rate) to those in the North Atlantic. We will take u-channel samples from the archives halves of U1486 and U1489 and measure the magnetic susceptibility and demagnetization behaviors of the natural remanent magnetization (NRM), anhysteretic remanent magnetization (ARM) and isothermal remanent magnetization (IRM) at centimeter scale. We will use these data to generate characteristic remanent directions and generate estimates of RPI over long Pleistocene and Pliocene timeframes. The 1.25 Myr equatorial Pacific marine sediment record from Site U1486 can be queried for evidence of non-axial-dipole structure and regional heterogeneities at a resolution several times higher than existing records and stacks and is more similar to high quality North Atlantic records. Site U1489 contains a 5 Myr record of sedimentation that will be developed into the longest continuous RPI record ever produced. Preliminary data suggest it is of remarkable fidelity and, when paired with the d18O benthic foraminifer stratigraphy being developed concurrently for this site, can potentially become the type record for Pliocene geomagnetic field behavior. Not only will this record be a magnetostratigraphic tuning target for the Pliocene, it will also inform inquiries into geomagnetic field evolution and organization over the scale of (sub-)orbital variations to full chrons and epochs. RPI-assisted chronologies will be developed for the mid-late Pleistocene records of both U1486 and U1489 (through correlation to existing global stacks) that can then be tandemly tuned with d18O records to develop robust chronologies and the establishment of a strong chronostratigraphic framework to directly facilitate the science objectives of IODP Expedition 363.