Transforming our understanding of the geodynamo: A new global synthesis and model of millennial-scale geomagnetic variability for late Pleistocene

地球磁场对我们星球上的生命和现代社会所依赖的电子通信技术是必不可少的，因为它提供了免受有害宇宙射线和轰炸高层大气的太阳风的保护。但这种看不见的保护领域远非一成不变。它的强度和方向总是在时间和空间上变化的。在十年甚至更长的时间尺度上，这些变化可以归因于地球围绕其轴的自转和其熔融内部的对流运动--地球发电机--之间的相互作用。然而，我们对地球发电机及其驱动磁场变化的机制的理解是原始的。阻碍进展的主要问题是缺乏一个强大的数据集来记录过去磁场的变化，这些变化可以追溯到全新世地质时代(约10,000年前)之后。对于全新世，我们有一个相对准确的记录汇编，主要来自考古和湖泊档案，显示了来自世界各地遗址网络的磁场强度和方向的变化。这使我们能够开发全球磁场随时间变化的计算机模型，提供了一种改变我们对地球发电机的理解的方法。但我们必须把目光投向全新世以外，因为我们需要更长远的视角来研究更全面的领域变异性。自罗马时代以来，地球磁场已经失去了一半的强度，但在全新世(更新世)之前的地质时代，地球磁场的强度发生了更大的变化。此外，也不存在无可争辩的满分(180度)。磁场方向或磁极漂移的变化持续了约40年，该事件只是在过去约500年期间发生的至少五次有充分记录的漂移之一。我们建议通过转向这一晚更新世磁场强度和方向变化的记录来改变我们对地球发电机和地球磁场变化原因的理解。海洋沉积物钻探岩心非常适合提供这一目的所需的长期不受干扰的记录，但到目前为止，还不可能充分可靠地确定它们的年代，以便在全球范围内以所需的分辨率工作。我们将：(1)利用最近在西伊比利亚边缘钻探的一套特殊的沉积物档案，建立过去50万年来地磁变化的新基准记录(KYR)。(2)对全球已有的高分辨率沉积古地磁记录进行综合综合。(3)利用伊比利亚边缘沉积物独特的年代学限制，准确地确定Exp的年代。千禧年规模的339项记录。然后，我们将使用可用的地球化学性质/物理性质数据集将该年表输出到合成记录中，以开发出过去~500KYR磁场强度和方向变化的精确日期全球汇编。这种对比方法确保了我们不会对站点间古地磁变化的同步性做出假设(以便研究这一问题)。(4)与领先的地磁场模型师合作，使用这些新的高分辨率和日期准确的数据集来建立第一个计算机模型，以重建过去数百年来地球地磁场在时间和空间上的变化，以彻底改变我们对地磁变化的动力学和原因的理解。

Earth's magnetic field is essential to life on our planet and to electronic communication technologies upon which modern society depends because it provides protection from harmful cosmic rays and the solar wind that bombard the upper atmosphere. But this invisible protective field is far from constant. Its intensity and direction are always changing both temporally and spatially. On decadal timescales and longer these changes can be attributed to the interaction between Earth's rotation about its axis and convective motion in its molten interior- its geodynamo. Yet our understanding of the geodynamo and the mechanisms by which it drives changes in our magnetic field is primitive. The main problem preventing progress is a lack of a robust data set recording past changes in magnetic field that extends back in time beyond the start of the Holocene geological epoch (~10,000 years ago, ka). For the Holocene, we have a relatively well dated compilation of records, largely from archaeological and lake archives, showing changes in magnetic intensity and direction from a network of sites around the world. This allows us to develop computer models of global magnetic field variability through time, providing a way to transform our understanding of the geodynamo. But we must look beyond the Holocene because we need a longer perspective to study a fuller range of field variability. Earth's magnetic field has lost half its strength since Roman times but much larger changes in intensity occurred during the geological epoch that preceded the Holocene (the Pleistocene). Furthermore, there has not been an undisputed full (180 deg.) change in magnetic field direction or polarity excursion for ~40 kyrs and that event is just one of at least five well-documented excursions that took place during the last ~500 kyrs. We propose to transform our understanding of the geodynamo and the cause of changes in Earth's magnetic field by turning to this Late Pleistocene record of changes in field intensity and direction. Marine sediment drillcores are well-suited to providing the long undisturbed records needed for this purpose but, until now, it has not been possible to date them sufficiently robustly to work globally at the resolution needed. We will: (1) Build a new benchmark record of geomagnetic change for the last ~500 thousand years (kyr) using a suite of exceptional sediment archives recently drilled on the west Iberian Margin. (2) Undertake a comprehensive synthesis of existing high-resolution sedimentary palaeomagnetic records around the globe. (3) Take advantage of the unique chronological constraints of the Iberian Margin sediments, to precisely date the Exp. 339 records at the millennial scale. We will then export that chronology to the synthesized records using geochemical/physical property data sets available to develop a precisely dated global compilation of changes in magnetic field intensity and direction for the last ~500 kyr. This correlation method ensures that we make no assumption about synchronicity of palaeomagnetic change between sites (so that this issue can be studied). (4) Use these new high-resolution and well-dated datasets in collaboration with a leading geomagnetic field modeler to build the first computer models to reconstruct changes in Earth's geomagnetic field through time and space over the last few hundred kyr to overhaul our understanding of the dynamics and causes of geomagnetic variability.