500,000 years of solar irradiance, climate and vegetation changes

即将到来的太阳辐射最终决定着地球系统内的能量总量。我们对太阳辐射如何受地球轨道路径调制的理解，巩固了我们通过地质记录对长期(10000年)全球气候和植被变化的理解。然而，没有以10000年为时间尺度的太阳辐照度的独立的长期经验记录。我们的提议旨在通过将尖端的有机地球化学技术应用于过去植被变化的独特热带记录来产生第一个地球表面的太阳辐射变化记录。目前对太阳通量的理解是基于观测到的宇宙成因同位素(10Be和14C)的变化；然而，这些技术的应用时间范围受到各自同位素的半衰期的限制。我们对花粉/孢子化学成分了解的最新进展表明，生长过程中最大紫外线B(UV-B)辐射的特征被锁定并保存在孢粉化学结构中[1]。由于UV-B与到来的太阳总辐射成正比，这为从化石花粉/孢子记录中提取太阳辐射通量的长期记录提供了机会。在第四纪期间(过去260万年)，轨道强迫已被确定为与与冰期-间冰期循环有关的气候和植被变化特别重要[2]。然而，由于缺乏合适的研究地点，我们对多个冰期-间冰期周期中陆地植被变化的了解仍然有限。国际大陆科学钻探计划从博苏姆特维湖(加纳)连续发现了100万年的沉积记录，新的化石花粉/孢子数据提供了这一时期非洲植被变化的第一个陆地记录[3]。博苏姆特维湖研究地点提供了一个评估太阳辐射、气候和植被随时间变化的理想机会，因为它处于很好的位置，记录了全球气候系统(热带间汇合区，季风)和植被(在化石花粉记录中观察到森林和热带草原生物群之间的变化)的变化。我们将使用傅立叶变换红外光谱来分析过去50万年博苏姆特维湖沉积物记录中500个不同深度(年龄)中提取的约15,000个花粉/孢子的化学结构。通过描述过去地球表面太阳辐照度的变化，并将化学变化与现有的模型和植被数据进行比较，我们将对变化模式提供新的见解。太阳辐照度的独立记录将允许在化石记录中分离气候和植被变化的推断。因此，我们将有可能确定地球系统内的领先和滞后(因果关系)，例如气候系统中与植被变化有关的变化是如何发生的。研究小组拥有所有必要的技能和经验来提出建议：Gosling(Pi OU)研究热带过去的环境变化已有12年，自2007年以来一直致力于博苏姆特维湖沉积物；Lomax(Pi Univ.Nottingham)和Fraser(Res Co-I OU)是研究花粉/孢子化学成分变化及其在地质记录中保存的先驱。地球、行星、空间和天文学研究中心(OU)将提供所需的设施和研究环境。REFS：[1]Lomax，B.H.等人，植物孢子壁，作为紫外线-B辐射长期变化的记录。《自然地理》，2008年。1：592-596。[2]海斯，J.D.等人，《地球轨道上的变化：冰河时代的标尺》。《科学》，1976年。194：1121-1132。[3]Koeberl，C.等人，2004年ICDP博苏姆特维陨石坑钻探项目。气象台。行星。《科学》，2007。42：483-511。

Incoming solar irradiance ultimately governs the amount of energy within the Earth's system. Our understanding of how solar irradiance is modulated by the Earth's orbital pathway underpins our understanding of long-term (>10,000 year) global climate and vegetation change through the geological record. However, there is no independent long-term record empirical record of solar irradiance on timescales >10,000 years. Our proposal is designed to generate the first record of solar irradiance change at the Earth's surface by applying cutting-edge organic geochemical techniques to a unique tropical record of past vegetation change.Current understanding of solar flux is based upon changes observed in cosmogenic isotopes (10Be and 14C); however, the temporal range over which these techniques can be applied is limited by the half-lives of the respective isotopes. Recent advances in our understanding of pollen/spore chemical composition indicate that a signature of maximum Ultra Violet-B (UV-B) radiation exposure during growth is locked-in, and preserved, within the sporopollenin chemical structure [1]. As UV-B is directly proportional to total incoming solar irradiance this offers an opportunity to extract a long-term record of solar irradiance flux from the fossil pollen/spore record.During the Quaternary period (last 2.6 million years) orbital forcing has been identified as particularly important in relation to climate and vegetation change associated with glacial-interglacial cycles [2]. However, due to a paucity of appropriate study sites our understanding of terrestrial vegetation change over multiple glacial-interglacial cycles remains limited. New fossil pollen/spore data from a continuous c. 1 million year sedimentary record recovered from Lake Bosumtwi (Ghana), recovered by the International Continental Scientific Drilling Program, provides the first terrestrial record of vegetation change in Africa during this period [3]. The Lake Bosumtwi study site offers an ideal opportunity to assess how solar insolation, climate and vegetation have changed through time because it is well placed to record changes in the global climate system (Inter Tropical Convergence Zone, monsoon) and vegetation (shifts between forest and savannah biome are observed in the fossil pollen record).We will use Fourier Transformed Infra-Red spectroscopy to analyse the chemical structure of c. 15,000 pollen/spores extracted from 500 different depths (ages) in the Lake Bosumtwi sediment record over the last 500,000 years. By characterizing past change in solar irradiance at the Earth's surface and comparing chemical change with existing model and vegetation data we will provide new insights into the pattern of change. The independent record of solar irradiance will allow climate and vegetation change inferences to be decoupled within the fossil record. Therefore, we will have the potential to determine leads and lags (causality) within the Earth's system, e.g. how do shifts in climate systems related to vegetation change.The research team have all the requisite skills and experience to deliver the proposal: Gosling (PI OU) has worked on past environmental change in the tropics for 12 years and has worked on Lake Bosumtwi sediments since 2007; Lomax (PI Univ. Nottingham) and Fraser (Res Co-I OU) are organic geochemists who have pioneered research into pollen/spore chemical composition change and its preservation in the geological record. The Centre for Earth, Planetary, Space & Astronomical Research (The OU) will provide the required facilities and research environment.REFS: [1] Lomax, B.H. et al., Plant spore walls as a record of long-term changes in ultraviolet-B radiation. Nature Geosci., 2008. 1: 592-596. [2] Hays, J.D. et al., Variations in the Earth's orbit: Pacemaker of the ice ages. Science, 1976. 194: 1121-1132. [3] Koeberl, C., et al., The 2004 ICDP Bosumtwi Crater Drilling Project. Meteorit. Planet. Sci., 2007. 42: 483-511.