Global Records of the Iceland Basin Geomagnetic Excursion
冰岛盆地地磁偏移的全球记录
基本信息
- 批准号:NE/G001391/1
- 负责人:
- 金额:$ 5.41万
- 依托单位:
- 依托单位国家:英国
- 项目类别:Research Grant
- 财政年份:2008
- 资助国家:英国
- 起止时间:2008 至 无数据
- 项目状态:已结题
- 来源:
- 关键词:
项目摘要
The Earth's magnetic field varies on a number of different timescales. On short timescales of years to centuries the magnetic poles drift around the geographic poles, in a process known as secular variation. Hence, the magnetic pole is rarely at the geographic pole, and this why magnetic compasses are adjusted for this variation before they can be used for navigation. If the location of the magnetic poles is averaged over longer timescales of about 10,000 years the mean positions coincide with those of the geographic poles. On very long time scales of millions of years the Earth's magnetic field is known to reverse its polarity, and compasses would point to the south rather than to the north. These reversals do not occur regularly and the duration of the different polarities varies enormously. We are currently in a period of 'normal polarity' (i.e. compasses point to the north) and the last reversal of the field was about 780,000 years ago. Geomagnetic excursions occur on timescales between secular variation and field reversals. During a geomagnetic excursion the magnetic poles wander far away (>45 dgerees) from the geographic poles, but return to their previous location. This distinguishes them from full reversals where the magnetic pole wanders far away from the geographic pole, before settling at the opposite geographic pole. There have been suggestions that there have been up to 12 such excursions in the last 780,000 years (i.e. since the last reversal), and because they are global events, they can be used to correlate different sedimentary sequences worldwide. The excursions are also marked by a decrease in the overall intensity of the Earth's magnetic field. This field shields us from incoming solar radiation, and we have recently shown that excursions are marked by an increase in the rate of production of radionuclides in the atmosphere, due to the increased incoming solar radiation that results from the reduction in field strength. Such radionuclides are preserved in sediments and in ice cores, and potentially offer a way of correlating ice-core records of climate change with patterns of climate change recognised in marine sediments. An understanding of the causes of geomagnetic excursions, how long they last, and how useful they can be for correlating different climate events has been hampered by a lack of good records of these events. They are typically recognised in the magnetic signal from sediments, where the Earth's magnetic field aligns magnetic minerals during their incorporation into the sediment, or when magnetic minerals grow during formation of the rocks. Because they are thought to be of short duration we need sediments that accumulate at a rapid rate. We have recently shown that one of these excursions known as the Iceland Basin Event, which took place about 186,000 years ago, lasted for about 7000 years, based on analyses of two sediment cores from the Atlantic. Other authors have proposed shorter and longer durations for the same event. Our proposal aims to study the magnetic signal for five other cores, scattered through the Atlantic and Pacific oceans, and spread over a range of latitudes. This will enable us to assess the global nature of the signal. We will also be carrying our geochemical analyses that will enable us to calculate the duration of the event. Recent work has shown that the magnetic instabilities associated with reversals appear to only last 2,000 years at the equator, and about 10,000 years at the geographic poles. We will be able to test if the same holds true for geomagnetic excursions. Finally, a knowledge of the duration of these events will inform climate scientists as to the resolution that excursions can offer their correlations of climate records. Short durations will offer very precise correlation, but are harder to identify, whereas long durations should be easier to find and identify but offer correlation at a much lower precision.
地球磁场在许多不同的时间尺度上变化。在几年到几个世纪的短时间尺度上,磁极围绕地理两极漂移,这一过程被称为长期变化。因此,磁极很少在地理极点,这就是为什么磁罗盘在用于导航之前要根据这种变化进行调整。如果将磁极的位置在更长的时间尺度(约1万年)上取平均值,则其平均位置与地理磁极的位置一致。众所周知,在数百万年的漫长时间尺度上,地球磁场的极性会发生逆转,指南针会指向南方而不是北方。这些逆转并不经常发生,不同极性的持续时间差别很大。我们目前正处于“正常极性”时期(即指南针指向北方),磁场的最后一次反转大约发生在78万年前。地磁漂移发生在长期变化和磁场反转之间的时间尺度上。在地磁偏移期间,磁极偏离地理极点很远(约45度),但又回到原来的位置。这与地磁完全倒转不同,地磁完全倒转是指磁极在离地极很远的地方徘徊,然后在相对的地极安定下来。有人认为,在过去的78万年(即自上一次逆转以来),有多达12次这样的漂移,因为它们是全球性的事件,它们可以用来联系世界范围内不同的沉积序列。这种偏移的另一个特征是地球磁场总强度的减弱。这个磁场保护我们不受入射太阳辐射的影响,我们最近已经表明,由于磁场强度降低导致入射太阳辐射增加,因此大气中放射性核素的产生速度增加,这是偏移的标志。这些放射性核素保存在沉积物和冰芯中,并可能提供一种将冰芯气候变化记录与海洋沉积物中公认的气候变化模式相关联的方法。由于缺乏对这些事件的良好记录,对地磁漂移的原因、持续时间以及它们对不同气候事件的相关性有多大用处的理解受到了阻碍。它们通常在沉积物的磁信号中被识别出来,在沉积物中,地球的磁场在磁性矿物结合到沉积物中,或者当磁性矿物在岩石形成过程中生长时,它们就会对齐。因为它们被认为持续时间很短,所以我们需要快速积累的沉积物。根据对大西洋两个沉积物岩心的分析,我们最近表明,其中一次被称为冰岛盆地事件的远足发生在大约18.6万年前,持续了大约7000年。其他作者提出了缩短或延长同一事件的持续时间。我们的提案旨在研究其他五个地核的磁信号,这些地核分散在大西洋和太平洋中,并分布在一系列纬度上。这将使我们能够评估信号的全局性质。我们还将进行地球化学分析,这将使我们能够计算出事件的持续时间。最近的研究表明,与地磁倒转有关的磁场不稳定性似乎只在赤道持续2000年,而在地理两极大约持续1万年。我们将能够测试是否同样适用于地磁漂移。最后,对这些事件持续时间的了解将使气候科学家了解短途旅行可以提供气候记录的相关性。较短的持续时间将提供非常精确的相关性,但很难识别,而较长的持续时间应该更容易找到和识别,但提供的相关性的精度要低得多。
项目成果
期刊论文数量(4)
专著数量(0)
科研奖励数量(0)
会议论文数量(0)
专利数量(0)
High-resolution record of the Laschamp geomagnetic excursion at the Blake-Bahama Outer Ridge
布莱克-巴哈马外脊拉尚地磁偏移的高分辨率记录
- DOI:10.1093/gji/ggt327
- 发表时间:2013
- 期刊:
- 影响因子:2.8
- 作者:Bourne M
- 通讯作者:Bourne M
In-phase anomalies in Beryllium-10 production and palaeomagnetic field behaviour during the Iceland Basin geomagnetic excursion
- DOI:10.1016/j.epsl.2007.10.051
- 发表时间:2008-01-30
- 期刊:
- 影响因子:5.3
- 作者:Knudsen, Mads Faurschou;Henderson, Gideon M.;Kubik, Peter W.
- 通讯作者:Kubik, Peter W.
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Conall MacNiocaill其他文献
Conall MacNiocaill的其他文献
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{{ truncateString('Conall MacNiocaill', 18)}}的其他基金
Integrated Understanding of the Early Jurassic Earth System and Timescale (JET)
早期侏罗世地球系统和时间尺度的综合理解(JET)
- 批准号:
NE/N018478/1 - 财政年份:2016
- 资助金额:
$ 5.41万 - 项目类别:
Research Grant
Doctoral Training Grant (DTG) to provide funding for 1 PhD studentship.
博士培训补助金 (DTG) 为 1 名博士生提供资助。
- 批准号:
NE/H526978/1 - 财政年份:2009
- 资助金额:
$ 5.41万 - 项目类别:
Training Grant
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