Archeomagnetism of Southern Africa: Implications for Longevity of the South Atlantic Anomaly

南部非洲的考古地磁学：对南大西洋异常长期存在的影响

基本信息

批准号：
1448227
负责人：
John Tarduno
金额：
$ 31万
依托单位：
University of Rochester
依托单位国家：
美国
项目类别：
Standard Grant
财政年份：
2015
资助国家：
美国
起止时间：
2015-03-01 至 2019-02-28
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=1448227&HistoricalAwards=false
关键词：
Archeomagnetism Southern Africa Implications Longevity

项目摘要

A broad low intensity area in Earth's recent magnetic field spans the southern Atlantic Ocean, Africa and South America. This is commonly called the South Atlantic Anomaly (SAA). The SAA allows a relatively close approach of Earth's radiation belts, affecting spacecraft operations. The low magnetic intensity decreases the efficiency of magnetic shielding in the region, which can influence atmospheric ozone. Many believe the SAA is linked to the dramatic decay of the dipole geomagnetic field intensity during the last 160 years, and the growth of an area of reversed magnetic field on Earth's core beneath South Africa. Some have even speculated Earth is heading toward a geomagnetic field reversal. But understanding these phenomena within the context of longer-term geomagnetic history has been limited by a lack of Southern Hemisphere archeomagnetic data (that is, data from archeological objects that were fired to high temperature and subsequently preserved a record of Earth's magnetic field as they cooled). Our research and education program is aimed at understanding the history of the geomagnetic field in the SAA region as recorded in southern Africa. The main focus of the work is the collection and subsequent analysis of archeomagnetic data from Iron Age burnt structures, and tests of models addressing how the nature of the boundary between Earth's core and mantle may be giving rise to recent changes seen in the geomagnetic field.Archeomagnetic data from Iron Age sites of southern Africa (ca. 1000-1650 AD) show a sharp intensity drop at 1300 AD, at a rate comparable to modern field changes in the present-day South Atlantic Anomaly (SAA), but to lower values. The recurrence of low field values may reflect magnetic flux expulsion from the core promoted by the unusual core-mantle boundary composition and structure beneath southern Africa defined by seismology (specifically the African Large Low Velocity Seismic Province, or LLVSP). Because the African LLVSP is a longstanding structure, this region might be a steady site of flux expulsion, and perhaps the triggering site for geomagnetic reversals, on time scales of millions of years. If correct, this conceptual model is transformative because it suggests reversals do not initiate at random locations, but instead nucleate at core-mantle boundary sites that promote flux to leak upward. The model predicts modulation of the field on time scales of the lifetime of an eddy in the core flow, and will be tested by extending the archeomagnetic record of Iron Age southern Africa. The research program is integrated with undergraduate and graduate education and will be conducted with geologists and archeologists from South Africa, Botswana, and Zimbabwe. This project was co-funded by the GVF fund in the Office of International Science Engineering.

地球最近磁场的一个广泛的低强度区域横跨南大西洋，非洲和南美。这通常称为南大西洋异常（SAA）。 SAA允许地球辐射带相对接近，影响航天器操作。低磁强度降低了该地区磁性屏蔽的效率，这会影响大气中的臭氧。许多人认为，SAA与过去160年中偶极磁磁场强度的戏剧性衰减有关，以及在南非下地球核心上逆转磁场区域的增长。有些人甚至猜测地球正朝着地磁场逆转。但是，在长期地磁历史的背景下了解这些现象受到了由于缺乏南半球考古磁数据的限制（即，来自考古对象的数据被发射到高温并随后在冷却时保留了地球磁场的记录）。我们的研究和教育计划旨在了解南部非洲记录的SAA地区地磁领域的历史。这项工作的主要重点是对铁器时代燃烧结构的考古磁数据的收集和后续分析，以及对地球核心和地幔之间边界性质的模型的测试，可能会导致地磁领域中看到的最新变化。在南部非洲的铁器时代，在1000-1650 AD的范围内，ARCHEOMAGNETIC PROPATION中的ARCHEOMAGNETIC PROPATION（1000-1650）的范围（1000-1650）显示了1300年的范围。当今的南大西洋异常（SAA），但值较低。低场值的复发可能反映出由核心掩体边界组成和南部非洲下方的结构所推动的磁通量驱动（特别是非洲大型低速地震省或LLVSP）。由于非洲LLVSP是一个长期存在的结构，因此该区域可能是驱动的稳定地点，也许是数百万年的时间尺度的触发地点逆转的触发地点。如果正确的话，这种概念模型是变革性的，因为它表明逆转不会在随机位置启动，而是在核心掩形边界位点成核，以促进通量以向上泄漏。该模型可以预测核心流中涡流的寿命的时间尺度对田地的调制，并将通过扩展南部非洲铁器时代的考古磁记录来测试。该研究计划与本科和研究生教育融为一体，并将与来自南非，博茨瓦纳和津巴布韦的地质学家和考古学家进行。该项目是由GVF基金在国际科学工程办公室共同资助的。