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.

本课题拟在热带东非5个湖泊（图尔卡纳、马拉维、坦噶尼喀、爱德华、维多利亚）开展全新世古磁场长期变化（PSV）研究。我们将从每个湖泊至少两个沉积物岩心中恢复PSV记录，并从中开发复合PSV定向记录。我们将关联所有五个湖泊的定向PSV记录，并对记录进行C14测年。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，我们至少可以在马拉维的一个湖泊上做到这一点。这项工作将使我们能够开发一组区域PSV时间序列，以表征高分辨率几乎一无所知的区域的场变异性。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，以评估地球动力学。南加州大学的研究人员基于过去8000年的全球PSV时间序列，开发了一个全新世场变率的新模型（PSVMOD2.0）。PSVMOD2.0目前在全球有85个站点，产生72个方向PSV时间序列和35个古强度时间序列。然而，PSVMOD2.0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。对非洲湖泊的研究将显著提高PSVMOD2.0的质量。非洲PSV数据还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格局。PSV以前在古气候研究中被非常有效地用作高分辨率相关和定年工具。PSVMOD2.0应该成为各种科学家使用的社区数据库，以便更好地了解PSV和地球动力学。我们仍然不太了解我们的行星磁场在正常情况下是如何工作的（主要是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/恒星表面以下的导电流体流动（发电机作用）产生的，但这些过程的当前模型（发电机模型）并没有充分描述这些磁场的实际运作方式（特别是地球磁场和太阳磁场）。我们需要更全面地了解磁场在正常条件下是如何运作的，以便更好地约束未来的发电机模型。要做到这一点，最好（也是唯一）的方法是重建我们的领域在过去几千年里是如何变化的。（年代的错误使得这种分析在古代很难甚至不可能进行。）在过去的几千年里，我们在不到一半的地球表面上测量了地球磁场的变化。这个项目填补了我们对中非大陆认识上的一个大空白。更好地了解地球磁场的正常运作方式（过去几千年）也将给我们一个更好的方法来评估地球磁场在“扭曲”时的情况。这些周期被称为磁场偏移和磁场倒转。