Filling Holes in the Holocene Geomagnetic Field - Tropical East Africa

填补全新世地磁场的空洞 - 热带东非

• 批准号: 1316507
• 负责人: Steven Lund
• 金额: $ 20万
• 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: 2013
• 资助国家: 美国
• 起止时间: 2013-08-01 至 2016-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1316507&HistoricalAwards=false
• 关键词: Filling; Holes; Holocene; Geomagnetic; Field

This proposal will carry out Holocene paleomagnetic field secular variation (PSV) studies on five lakes from Tropical East Africa (Turkana, Malawi, Tanganyika, Edward, Victoria). We will recover PSV records from at least two sediment cores in each lake and develop a composite PSV directional record from them. We will correlate the directional PSV records from all five lakes and date the records with C14 dating. We will also attempt to reconstruct relative paleointensity variability from each lake. Our preliminary data suggest we can do this for at least one lake, Malawi. This work will permit us to develop a regional group of PSV time series that will characterize field variability in a region where almost nothing is known in high-resolution. A high-resolution relative paleointensity record from Lake Malawi (10°S) would be the first such Holocene record from the Southern Hemisphere. The study will analyze these records and compare them with other global Holocene PSV data to assess geodynamo dynamics. USC researchers have developed a new model of Holocene field variability (PSVMOD2.0), based on a family of Global PSV time series for the last 8000 years. PSVMOD2.0 now has 85 sites around the World, which yield 72 directional PSV time series and 35 paleointensity time series. However, PSVMOD2.0 has no significant data from the African continent and no paleointensity time series from the Southern Hemisphere. This study of African lakes will add significantly to the quality of PSVMOD2.0. The African PSV data will also be used to better assess the timing and regional pattern of Holocene climate change in the studied lakes. PSV has previously been used very effectively as a high-resolution correlation and dating tool in paleoclimate studies. PSVMOD2.0 should become a community database used by a variety of scientists to better understand PSV and geodynamo dynamics. We still do not understand very well how our planetary magnetic field works (and largely the way all planetary magnetic fields and stellar magnetic fields work) under normal conditions. We know that these magnetic fields are generated by flow of electrically conducting fluid below the planetary/stellar surfaces (dynamo action), but current models of these processes (dynamo models) do not adequately describe how these fields really operate (particularly the Earth's magnetic field and our Sun's magnetic field). We need a more complete understanding of how our magnetic field operates under normal conditions to better constrain future dynamo models. The best (and only) way to do that is to reconstruct how our field has varied over the last several thousand years. (Dating errors make this analysis difficult to impossible in older times.) We currently have measured variations in Earth's magnetic field over the last few thousand years over less than half the Earth's surface. This project fills in a big hole in our understanding the central African continent. Better understanding of how the Earth's magnetic field operates normally (last few thousand years) will also give us a better way to assess what the Earth's magnetic field is doing when it 'goes screwy'. These periods are called magnetic field excursions and reversals.

该项目将对热带东非的五个湖泊（图尔卡纳、马拉维、坦噶尼喀、爱德华、维多利亚）进行全新世古地磁场长期变化（PSV）研究。我们将从每个湖泊的至少两个沉积物岩心中恢复PSV记录，并从中开发一个复合PSV方向记录。我们将把来自所有五个湖泊的定向PSV记录与C14测年记录相关联。我们还将尝试重建每个湖泊的相对古强度变化。我们的初步数据表明，我们至少可以对马拉维的一个湖泊这样做。这项工作将使我们能够开发一个区域组的PSV时间序列，将表征字段的变化在一个地区，几乎没有什么是已知的高分辨率。 来自马拉维湖（10°S）的高分辨率相对古强度记录将是南半球第一个这样的全新世记录。该研究将分析这些记录，并将其与其他全球全新世PSV数据进行比较，以评估地球发电机动力学。南加州大学的研究人员开发了一种新的全新世场变率模型（PSVMOD 2.0），该模型基于过去8000年的全球PSV时间序列。PSVMOD 2.0目前在全球有85个站点，产生了72个方向PSV时间序列和35个古强度时间序列。然而，PSVMOD 2.0没有来自非洲大陆的重要数据，也没有来自南半球的古强度时间序列。这项对非洲湖泊的研究将大大提高PSVMOD 2.0的质量。非洲PSV数据也将用于更好地评估所研究湖泊全新世气候变化的时间和区域模式。PSV在古气候研究中曾被有效地用作高分辨率对比和定年工具。PSVMOD 2.0应该成为各种科学家使用的社区数据库，以更好地了解PSV和地球发电机动力学。我们仍然不太了解我们的行星磁场在正常条件下是如何工作的（以及所有行星磁场和恒星磁场的工作方式）。我们知道这些磁场是由行星/恒星表面下的导电流体流动产生的（发电机作用），但这些过程的当前模型（发电机模型）并不能充分描述这些场的真正运作（特别是地球的磁场和我们的太阳的磁场）。我们需要更全面地了解我们的磁场在正常条件下如何运作，以更好地约束未来的发电机模型。要做到这一点，最好的（也是唯一的）方法是重建我们的领域在过去几千年中是如何变化的。（日期错误使得这种分析在旧时代很难甚至不可能。我们目前已经在不到一半的地球表面上测量了过去几千年来地球磁场的变化。这个项目填补了我们对中非大陆了解的一个大洞。更好地了解地球磁场如何正常运作（过去几千年）也将使我们有更好的方法来评估地球磁场在“扭曲”时的表现。这些周期被称为磁场偏移和反转。