Reconstructing solar activity and geomagnetic field intensity during the Holocene

重建全新世期间的太阳活动和地磁场强度

• 批准号: NE/E012531/1
• 负责人: Mads Knudsen
• 金额: $ 34.42万
• 依托单位: University of Oxford
• 依托单位国家: 英国
• 项目类别: Fellowship
• 财政年份: 2007
• 资助国家: 英国
• 起止时间: 2007 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FE012531%2F1
• 关键词: Reconstructing; solar; activity; geomagnetic; field

The Sun is by far the most important energy source for the Earth's climate system. Direct observations over the last four centuries have revealed that solar activity varies over time, and these variations appear to have played a significant role in forcing periods of climate change on Earth in the pre-industrial era, such as the Medieval Warm Period (900-1400 A.D.) and the Little Ice Age (1500-1800 A.D.). The longer-term variations in solar activity over the last 11,500 years (the Holocene period), and their potential links to climate change, remain very uncertain. The production of cosmogenic nuclides, such as 10Be and 14C, in the atmosphere is controlled by solar activity, implying that records of such nuclides from natural archives may extend our knowledge of solar variation back in time. Reconstruction of past solar activity is complicated, however, by the fact that the 10Be and 14C signals embedded in natural archives are also influenced by the intensity of Earth's magnetic field and by local climatic effects. Current efforts to reconstruct past solar activity are, therefore, hampered by uncertainties in reconstructing past geomagnetic field intensity and the limited availability of high-resolution 10Be and 14C records. The long-term solar variability remains a very controversial topic and there is a great need for alternative cosmogenic nuclide records to address this issue. With this proposal I will take a new approach to improve the current understanding of solar variability during the Holocene by generating new high-resolution records from different archives of past 10Be production rates combined with analyses of past variations in the intensity of the Earth's magnetic field. The main focus of this project will be to generate a high-resolution 10Be record from annually-layered (varved) lake sediments from west-central Sweden. The annual laminations of the sediment core I propose to study provide excellent chronological control, and a unique opportunity for determining the flux of 10Be to the surface of the Earth for the past 9,500 years. I will also develop a high-resolution 10Be record for the Holocene from marine sediments in the far North Atlantic. Based on the same marine sediments, I will also generate new extremely high-resolution records of the geomagnetic field behaviour during the past 11,500 years. My previous research has shown that the sediments from this location south of Iceland are well-suited for detailed studies of variations in 10Be production rates and geomagnetic intensity. Another aspect of this project will be to explore other archives of past 10Be deposition. The novel archives I wish to concentrate on include a raised peat bog from N. Ireland and a stalagmite from a cave in central China. Combining the new 10Be records from this study with existing 10Be records from polar ice cores, will make it possible to filter out local climatic effects embedded in the individual records and produce a global record of Holocene variations in 10Be production rate. Similarly, the new high-resolution records of the geomagnetic field behaviour will be integrated with existing magnetic data to produce a global estimate of Holocene geomagnetic field intensity. By correcting the combined 10Be curve for variations in the intensity of Earth's magnetic field, it is possible to reconstruct the solar activity during the Holocene. It will also be possible to assess potential changes in the carbon cycle during the Holocene by comparing the new global 10Be record with existing 14C records.

太阳是迄今为止地球气候系统最重要的能源。过去四个世纪的直接观测表明，太阳活动随着时间的推移而变化，而这些变化似乎在前工业时代的地球气候变化时期中发挥了重要作用，例如中世纪温暖期（公元900-1400年）和小冰河期（公元1500-1800年）。过去 11,500 年（全新世时期）太阳活动的长期变化及其与气候变化的潜在联系仍然非常不确定。大气中 10Be 和 14C 等宇宙成因核素的产生受太阳活动控制，这意味着自然档案中对此类核素的记录可以扩展我们对太阳变化的认识。然而，重建过去的太阳活动很复杂，因为自然档案中嵌入的 10Be 和 14C 信号也受到地球磁场强度和当地气候影响的影响。因此，当前重建过去太阳活动的努力受到重建过去地磁场强度的不确定性以及高分辨率 10Be 和 14C 记录的有限可用性的阻碍。长期的太阳变率仍然是一个非常有争议的话题，非常需要替代的宇宙成因核素记录来解决这个问题。通过这项提议，我将采取一种新方法，通过从过去 10Be 生产率的不同档案中生成新的高分辨率记录，并结合对过去地球磁场强度变化的分析，来提高目前对全新世期间太阳变化的理解。该项目的主要重点是从瑞典中西部每年分层（varved）的湖泊沉积物中生成高分辨率的 10Be 记录。我建议研究的沉积物核心的年度层状结构提供了极好的年代控制，并且为确定过去 9,500 年 10Be 到地球表面的通量提供了独特的机会。我还将从远北大西洋的海洋沉积物中开发全新世的高分辨率 10Be 记录。基于相同的海洋沉积物，我还将生成过去 11,500 年中地磁场行为的新的极高分辨率记录。我之前的研究表明，冰岛南部这个位置的沉积物非常适合详细研究 10Be 生产率和地磁强度的变化。该项目的另一个方面将是探索过去 10Be 沉积的其他档案。我希望重点关注的小说档案包括来自北爱尔兰的高地泥炭沼泽和来自中国中部洞穴的石笋。将本研究的新 10Be 记录与极地冰芯的现有 10Be 记录相结合，将有可能过滤掉单个记录中嵌入的局部气候影响，并生成全新世 10Be 生产率变化的全球记录。同样，地磁场行为的新高分辨率记录将与现有的磁数据相结合，以产生全新世地磁场强度的全球估计。通过校正地球磁场强度变化的组合 10Be 曲线，可以重建全新世期间的太阳活动。通过将新的全球 10Be 记录与现有 14C 记录进行比较，还可以评估全新世期间碳循环的潜在变化。