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.

对高质量观察的稀缺性，对对Geodynamo过程的更完整理解的重要局限性。最近的历史世俗变异（HSV）研究表征了短期HSV的全球模式，并将其变异性与核心发电机过程相关联。然而，古磁研究清楚地表明，地球的磁场经历了比历史时代所见的空间和时间变化范围要大得多。从观察的角度来看，我们对古磁性世俗变异的最完整理解来自全新世材料的古磁性研究。相比之下，更新世的高分辨率古磁性世俗变异（PSV）研究更为罕见。考古材料不存在；熔岩流是不连续的，很难约会。与全新世PSV记录相当的积累速率（50 cm/kyr）的积累速率和更新世沉积物序列很少被回收。因此，很少在完全理解其动力学所需的范围内仔细检查长期的PSV和外展场行为，这是完全千禧一代现象。为了缓解这一观察性数据差距，这对于南半球尤为普遍，这是对ODP腿202期间智利边缘沉积物的晚期近代地磁场行为的U通道古磁研究。地点1233（41度0 s，74度26W，水深838 m），1234（36度13 s，73度，40W，水深1015 m）和1235（36度9 s，73 d s，73 w，73 w，33 w，水深度489 m）恢复了累积率，累积率均可恢复为200 cy累积率。对这些序列全新世的古磁研究表明，这些沉积物提供了可靠，高质量的古磁性档案。在腿202腿上进行的船上研究表明，从全新世的底部到大约70 ka，记录PSV，相对古显着（RPI）和外展记录，以前所未有的时间分辨率。随着高积累速率（最高5年/cm）以及与这些沉积物相关的出色磁性，高分辨率独立的放射性碳年代和千禧一代基于气候的地层。基于U通道和离散样品的这三个站点的PSV记录提供了机会，可以重建最完整，最佳日期的晚期定向PSV的记录，相对古显着性以及有史以来从南半球恢复过的相关旅行，也许还有世界上任何地方。这些结果将描述具有前所未有的时间分辨率和独立时间顺序控制的地磁场强度，正常方向（PSV）和极端事件（偏移）之间的相互关系。特别是，这些沉积物保留了有史以来恢复的Laschamp游览（CA 41 KA）的最完全解决的记录，并将更好地了解其与正常的世俗变异，古显着性和外展场行为的关系。正在进行所有晚期更新世PSV记录的区域和全球及其比较，以评估数据质量和空间/时空变异性，以促进对这一最多（Laschamp游览）最近的地震磁性极端事件的低阶球形谐波分析。需要进行此类观察来测试地磁磁场可变性的时间尺度，旅行的起源和性质，与迪纳摩行为的关系以及对地球系统的重要性。