Testing the 'megadrought' hypothesis: the timing, cause and impacts of climate change in equatorial Africa (DeepCHALLA-UK)

检验“特大干旱”假说：赤道非洲气候变化的时间、原因和影响 (DeepCHALLA-UK)

• 批准号: NE/P011969/1
• 负责人: Christine Lane
• 金额: $ 84.78万
• 依托单位: University of Cambridge
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2017
• 资助国家: 英国
• 起止时间: 2017 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FP011969%2F1
• 关键词: Testing; megadrought; hypothesis; timing; cause

Over the last 25,000 years, East African climate has responded to changes in the Earth's orbit (mainly precession) that influence long-term variations in monsoonal rainfall and the migration of the intertropical convergence zone. But climate of earlier periods, back to 250,000 years, is less well understood as few continuous high resolution terrestrial records exist. This is a major gap in our understanding of equatorial climate from a region critical to the evolution of our own species. The African megadrought hypothesis states that droughts lasting many thousands of years occurred during the last interglacial (130,000 - 80,000 years ago) across tropical Africa. Evidence from the few sites investigated indicate they were of a severity greater than any droughts of succeeding time periods, and had major implications for evolutionary processes, for example continent wide migrations in Homo sapiens. Such long and intensely dry events in the history of African climate are an unexpected phenomenon, and their precise timing, origin and extent, has yet to be established. We hypothesise that megadroughts arose due to monsoon failure caused by changes in the shape of earth's orbit around the sun (the ~100,000 year eccentricity cycle), amplifying changes in the seasonal distribution of solar radiation (the ~21,000 year precession cycle). In order to fully understand these extreme climatic events, we will explore climate changes in the East African equatorial region spanning two glacial-interglacial cycles (i.e. the last ~250,000 years) giving critical context to the megadroughts and their causes. The project focuses on the sedimentary record from Lake Challa, a deep lake on the flank of Kilimanjaro. Unlike other studies from East Africa, the easterly position of Lake Challa places it beyond the direct influence of the Atlantic climate system, thus removing this aspect as a possible forcing and allowing us to isolate a record of monsoonal variation. The outstanding potential of these lake sediments to provide a long, sensitive repository of environmental change data has been established by a prior study of the last 25,000 years, that resulted in multi-disciplinary articles in 'Nature' on orbital forcing of climate, 'Science' on the laminated sediments and relation to ENSO, and 'Geology' concerning the seasonality of climate variations and the Kilimanjaro ice core. Additional data sets (published in other journals) confirm that the environmental proxies and dating methods proposed here will deliver a high quality record from this lake. The age of the deeper sediments has been estimated from seismic profiles of the sedimentary layers in the lake; new, absolute dates are required to identify the basal sediment age and rates of subsequent sedimentation. This project will lead in modelling of sediment ages from the new, deep cores through radiocarbon dates, palaeomagnetism to detect the presence of well-dated magnetic reversals and dating of volcanic ash layers through Ar/Ar dating and chemical correlation. Carbon and oxygen isotope data from diatom silica are excellent tools to reveal the megadroughts due to their sensitivity to humid/arid shifts as already demonstrated during the last 25,000 years.This project is part of an international consortium, partly funded by the International Continental scientific Drilling Program to recover cores from the lake. Our international partners have already gained support from their own national funding councils and will contribute complimentary environmental proxies (e.g. pollen, organic biomarkers) as well as additional dating (Ar/Ar) and, finally, climate modelling (ranging from local hydrology to global climate modelling) used to understand the global significance of our results in terms of forcing factors. We have Kenyan and Tanzanian collaborators, who will also act as conduits to ensure our discoveries help inform ongoing and future conservation needs and development strategies.

在过去的 25,000 年里，东非气候对地球轨道的变化（主要是进动）做出了反应，这些变化影响了季风降雨的长期变化和热带辐合带的迁移。但由于很少有连续的高分辨率陆地记录，人们对 25 万年前的早期气候知之甚少。这是我们对赤道气候的理解上的一个重大差距，该地区对我们自己物种的进化至关重要。非洲特大干旱假说指出，在最后一次间冰期（130,000 - 80,000 年前）整个热带非洲发生了持续数千年的干旱。来自少数调查地点的证据表明，它们的严重程度比随后时期的任何干旱都要严重，并且对进化过程具有重大影响，例如智人在整个大陆的迁徙。非洲气候历史上如此漫长而严重的干旱事件是一种意想不到的现象，其确切的时间、起源和范围尚未确定。我们假设，特大干旱是由于地球绕太阳轨道形状变化（约 100,000 年的偏心率周期）引起的季风衰竭而引起的，从而放大了太阳辐射季节性分布的变化（约 21,000 年的进动周期）。为了充分了解这些极端气候事件，我们将探索东非赤道地区跨越两个冰期-间冰期周期（即过去约 25 万年）的气候变化，为特大干旱及其原因提供重要背景。该项目重点研究查拉湖（乞力马扎罗山侧翼的一个深湖）的沉积记录。与东非的其他研究不同，查拉湖位于东部，使其不受大西洋气候系统的直接影响，从而消除了这一可能的强迫因素，使我们能够分离出季风变化的记录。这些湖泊沉积物具有提供长期、敏感的环境变化数据存储库的巨大潜力，这一点已由过去 25,000 年的一项先前研究证实，该研究在《自然》杂志上发表了有关气候轨道强迫的多学科文章，在《科学》杂志上发表了有关层状沉积物及其与 ENSO 关系的文章，在《地质学》杂志上发表了有关气候变化季节性和乞力马扎罗冰芯的文章。其他数据集（在其他期刊上发表）证实，此处提出的环境代理和测年方法将提供该湖的高质量记录。根据湖中沉积层的地震剖面估算了较深层沉积物的年龄；需要新的绝对日期来确定基底沉积年龄和随后的沉积速率。该项目将通过放射性碳测年、古地磁学来对新的深层岩心的沉积物年龄进行建模，以检测确定日期的磁反转的存在，并通过 Ar/Ar 测年和化学关联对火山灰层进行测年。来自硅藻的碳和氧同位素数据是揭示特大干旱的绝佳工具，因为它们对潮湿/干旱变化的敏感性在过去 25,000 年中已经得到证明。该项目是国际财团的一部分，部分资金由国际大陆科学钻探计划资助，旨在从湖中回收岩心。我们的国际合作伙伴已经获得了各自国家资助委员会的支持，并将提供免费的环境代理（例如花粉、有机生物标志物）以及额外的测年（Ar/Ar），最后，气候模型（从当地水文学到全球气候模型），用于了解我们的结果在强迫因素方面的全球意义。我们有肯尼亚和坦桑尼亚的合作者，他们也将充当渠道，确保我们的发现有助于为当前和未来的保护需求和发展战略提供信息。

项目成果

ICDP PROJECT DEEPCHALLA: RECONSTRUCTING ~250,000 YEARS OF CLIMATE CHANGE AND ENVIRONMENTAL HISTORY ON THE EAST AFRICAN EQUATOR

ICDP 项目 DEEPCHALLA：重建东非赤道约 25 万年的气候变化和环境历史

• DOI: 10.1130/abs/2017am-302533
• 发表时间: 2017
• 作者: Verschuren D

Reversed Holocene temperature-moisture relationship in the Horn of Africa.

• DOI: 10.1038/s41586-023-06272-5
• 发表时间: 2023-08
• 期刊: NATURE
• 影响因子: 64.8
• 作者: Baxter, A. J.;Verschuren, D.;Peterse, F.;Miralles, D. G.;Martin-Jones, C. M.;Maitituerdi, A.;van der Meeren, T.;Van Daele, M.;Lane, C. S.;Haug, G. H.;Olago, D. O.;Sinninghe Damste, J. S.
• 通讯作者: Sinninghe Damste, J. S.

The >250-kyr Lake Chala record: A tephrostratotype correlating archaeological, palaeoenvironmental and volcanic sequences across eastern Africa

• DOI: 10.1016/j.quascirev.2023.108476
• 发表时间: 2024-02
• 期刊: Quaternary Science Reviews
• 影响因子: 4
• 作者: C. Martin-Jones;C. Lane;Maarten Blaauw;Darren F. Mark;Dirk Verschuren;T. Van der Meeren;M. Van Daele;Hannah Wynton;Nick Blegen;Mary Kisaka;Melanie J. Leng;Philip A. Barker

History of scoria-cone eruptions on the eastern shoulder of the Kenya-Tanzania Rift revealed in the 250-ka sediment record of Lake Chala near Mount Kilimanjaro

乞力马扎罗山附近查拉湖 250ka 沉积物记录揭示了肯尼亚-坦桑尼亚裂谷东肩火山渣锥喷发的历史

• DOI: 10.1002/jqs.3140
• 发表时间: 2019
• 期刊: Journal of Quaternary Science
• 影响因子: 2.3
• 作者: Martin-Jones C

A ~250 KYR TEPHROSTRATIGRAPHY FROM THE DEEPCHALLA DRILLED LAKE RECORD: NEW CHRONOSTRATIGRAPHIC TIE-LINES BETWEEN PALAEOENVIRONMENTAL AND GEOARCHAEOLOGICAL SEQUENCES IN KENYA

来自 Deepchalla 钻探湖记录的约 250 KYR 地层学：肯尼亚古环境序列和地质考古序列之间新的年代地层联络线

• 发表时间: 2021
• 作者: Lane, C.S.