Collaborative Research: Pleistocene Geomagnetic Field Variability from the High-Latitude Southern Hemisphere

合作研究：南半球高纬度更新世地磁场变化

• 批准号: 0635348
• 负责人: Steven Lund
• 金额: $ 16.5万
• 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: 2007
• 资助国家: 美国
• 起止时间: 2007-01-01 至 2009-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0635348&HistoricalAwards=false
• 关键词: Collaborative; Research; Pleistocene; Geomagnetic; Field

A significant limitation toward a more complete understanding of the geodynamo process results from the scarcity of high quality observations. Recent historic secular variation (HSV) studies have characterized the global pattern of short-term HSV and have related its variability to the core dynamo process. Paleomagnetic studies make it clear, however, that the Earth's magnetic field has undergone a much wider range of spatial and temporal variations than have been seen in historic times. From an observational perspective, our most complete understanding of paleomagnetic secular variation has come from paleo-and archeomagnetic studies of Holocene materials. In contrast, high-resolution paleomagnetic secular variation (PSV) studies from the Pleistocene are much rarer. Archeological materials are absent; lava flows are discontinuous and difficult to date. And Pleistocene sediment sequences with accumulation rates comparable to Holocene PSV records ( 50 cm/kyr) have only rarely been recovered. Therefore, long-term PSV and excursional field behavior, which is exclusively a pre-Holocene phenomenon, are rarely scrutinized to the extent required for a full understanding of their dynamics. To alleviate this observational data gap, that is especially prevalent for the southern hemisphere, a u-channel paleomagnetic study of Late-Pleistocene geomagnetic field behavior from Chilean margin sediments cored during ODP Leg 202 is being undertaken. Sites 1233 (41 degrees 0 S, 74 degrees 26W, water depth 838 m), 1234 (36 degrees 13 S, 73 degrees 40W, water depth 1015 m), and 1235 (36 degrees 9 S, 73 degrees 33 W, water depth 489 m) recovered replicate sediment sequences with accumulation rates ranging from approximately 50 to 200 cm/kyr. Paleomagnetic studies on the Holocene part of these sequences demonstrate that these sediments provide a reliable and high quality paleomagnetic archive of geomagnetic behavior. Shipboard studies undertaken during Leg 202 show that the late-Pleistocene sediments, from the base of the Holocene to approximately 70 ka, record PSV, relative paleointensity (RPI) and excursional records at unprecedented temporal resolution. Along with the high accumulation rates (up to 5 yrs/cm) and excellent magnetic properties associated with these sediments, high-resolution independent radiocarbon chronologies and millennial climate based stratigraphies have been developed. PSV records from these three sites based on u-channel and discrete sample paleomagnetic measurements provide an opportunity to reconstruct the most complete and best dated record of late-Pleistocene directional PSV, relative paleointensity, and associated excursions ever recovered from the Southern Hemisphere and, perhaps, anywhere in the world. These results will describe the interrelationships between geomagnetic field intensity, normal directions (PSV), and extreme events (excursions) with unprecedented temporal resolution and independent chronologic control. Particularly, these sediments preserve the most completely resolved record of the Laschamp Excursion (ca 41 ka) ever recovered and will provide a better understanding of its relationship to normal secular variation, paleointensity and excursional field behavior. A regional and global inter-comparison of all late Pleistocene PSV records to assess data quality and space/time patterns of field variability is being undertaken to facilitate a low-order spherical harmonic analysis of this most (Laschamp Excursion) recent geomagnetic extreme event. Such observations are required to test concepts of timescales of geomagnetic field variability, the origin and nature of excursions, their relationship to dynamo behavior and there importance to the Earth system.

对地球发电机过程的更完整的理解的一个重要限制是缺乏高质量的观测结果。最近的历史长期变化（HSV）的研究特点的全球模式的短期HSV和相关的核心发电机过程的变化。然而，古地磁学研究清楚地表明，地球磁场经历了比历史时期更广泛的空间和时间变化。从观测的角度来看，我们对古地磁长期变化的最完整的理解来自于对全新世物质的古地磁和古地磁研究。相比之下，高分辨率的古地磁长期变化（PSV）的研究，从更新世要少得多。没有考古材料;熔岩流是不连续的，很难确定日期。更新世沉积物序列的积累速率相当于全新世PSV记录（50厘米/千年），只有很少被恢复。因此，长期的PSV和电磁场行为，这是一个专门的前全新世现象，很少仔细审查的程度需要充分了解他们的动态。为了缓解这一观测数据的差距，这是特别普遍的南半球，一个u通道古地磁研究晚更新世地磁场行为从智利边缘沉积物在ODP腿202取芯正在进行。网站1233（南纬41度，西经74度，水深838米），1234（南纬36度13分，西经73度40分，水深1015米），（南纬三十六度九，西经七十三度三十三，水深489米）恢复了重复的沉积物序列，积累速率约为50至200厘米/千年。对这些层序全新世部分的古地磁研究表明，这些沉积物提供了可靠和高质量的地磁行为古地磁档案。在202航次期间进行的船上研究表明，晚更新世沉积物，从全新世的基础约70 ka，记录PSV，相对古强度（RPI）和地震记录在前所未有的时间分辨率。沿着这些沉积物的高积累率（高达5 yrs/cm）和优异的磁性，高分辨率的独立放射性碳年代学和千年气候地层学已经发展起来。PSV记录从这三个网站的基础上u通道和离散样本古地磁测量提供了一个机会，重建最完整和最好的晚更新世定向PSV，相对paleotensity，以及相关的偏移记录以往任何时候都恢复从南半球，也许，在世界任何地方。这些结果将描述地磁场强度，正常方向（PSV）和极端事件（偏移）与前所未有的时间分辨率和独立的时序控制之间的相互关系。特别是，这些沉积物保存最完整的解决记录的Laschamp远足（约41万年）以往任何时候都恢复，并将提供一个更好的了解其关系到正常的长期变化，paleotensity和palsional场行为。正在进行一项区域性和全球性的所有晚更新世PSV记录的相互比较，以评估数据质量和场变的空间/时间模式，以便于对最近的地磁极端事件进行低阶球谐分析。这种观测需要测试地磁场变化的时间尺度的概念，漂移的起源和性质，它们与发电机行为的关系以及对地球系统的重要性。