Collaborative Research: The Lake Malawi Drilling Project - A long, high-resolution record of abrupt climate change in the southern tropics of East Africa

合作研究：马拉维湖钻探项目——东非南部热带气候突变的长期高分辨率记录

• 批准号: 0602350
• 负责人: Andrew Cohen
• 金额: $ 22.4万
• 依托单位: University of Arizona
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2006
• 资助国家: 美国
• 起止时间: 2006-09-15 至 2010-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0602350&HistoricalAwards=false
• 关键词: Collaborative; Research; Lake; Malawi; Drilling

Drilling the large rift lakes of the East African Rift Valley has been a high priority goal since the 1980s. In 2005 the Lake Malawi Scientific Drilling Project acquired more than 623 m of core at two sites (92% recovery), in seven holes, including one hole in 600 meters of water that reached a subbottom depth of 380 m. The project triple-cored a high-resolution site in the north basin, which extends back 80kyr, double cored the deep site in the central basin covering the past 200 kyr, and single-cored the deep site to 380 m, dated at 1.5 million years at the base. These drill-cores represent the longest, continuous record of high-resolution climate change available in the continental tropics, and they offer the potential to secure high-fidelity signals of East African effective moisture and temperature at a scale of decades/centuries over the length of the core. Located at the southern end of the East African Rift Valley (9S-14S), Lake Malawi's great depth (max. of 700 m), extent (more than 580 km long), and prolonged stratification with anoxic bottom waters assure well preserved, at times laminated, sediments recording regionally-significant southern hemisphere climate signals. This grant 1) addresses specific paleoclimate questions posed below, and 2) completes the initial core descriptions over the full duration of the cored interval. The research will address these paleoclimate questions: What was the direction, magnitude and timing of effective moisture, wind, and temperature change of this southern tropical setting, on a millennial scale, during the past two glacialinterglacial cycles? Do the observed shifts coincide in a consistent manner with SST variability in the tropical oceans, or with the North Atlantic thermohaline circulation? What is the lake level history of Malawi, and how does it compare with the methane record of the polar ice cores, which is interpreted to be a globally averaged measure of tropical moisture on the continents? Does the observed evidence for abrupt climate change in the Lake Malawi and other parts of East Africa coincide with known events from other regions on Earth, e.g., Heinrich or Dansgaard/Oeschger events? What are the direction, duration and magnitude of these changes? What was the tropical climate behavior during earlier periods of global warmth (e.g. Marine Isotope Stage 5e, or alternatively MIS 11), and how abruptly did these periods begin and end?The secondary objective is to complete the initial core descriptions, including reconnaissance sampling and analysis at low resolution over the past 1.5 million years. Did the climate of this site in the southern tropics respond only to changes in low-latitude precessional insolation (23-19 kyr) or also to high-latitude ice volume (100 kyr and 41 kyr) forcing, in the last part of the Pleistocene? Completing the reconnaissance, lowresolution analyses of this unique set of samples serves the greater scientific community, positioning it to undertake more elaborate studies on these cores in the future. Sampling and analyses are limited to key proxies, focused on quantifying past effective moisture, dust and temperature. Proxy analyses are carried out on a decade-century scale in the time intervals of selected events, and on a millennial scale over the broader intervals.The broader impact of this research addresses the role of climate on human evolution, assists in interpreting the tectonic history of the East African Rift, and leads to a better understanding of the controls of climate on species evolution in lakes. For instance, new Malawi records as well as those from other African sites indicate a period of pronounced aridity prior to ~75 kyr. Was this aridity crisis responsible for the early human population bottleneck in evidence for that period? This collaborative project engages scholars in-training at the postdoctoral, graduate, and undergraduate levels, as well as African colleagues, and involves outreach components both in Africa and the U.S.

自 20 世纪 80 年代以来，钻探东非大裂谷的大型裂谷一直是一个高度优先的目标。 2005 年，马拉维湖科学钻探项目在两个地点的七个孔中获得了超过 623 m 的岩心（采收率 92%），其中一个孔位于 600 米的水中，深度达到 380 m。该项目对北部盆地高分辨率站点进行三核，回溯80kyr，对中部盆地深部站点进行双核，覆盖近200kyr，单核深部站点至380m，可测年150万在基地的岁月。这些钻芯代表了大陆热带地区高分辨率气候变化的最长、连续记录，并且有可能在整个长度范围内获得东非有效湿度和温度的高保真信号。的核心。马拉维湖位于东非大裂谷 (9S-14S) 的南端，其深度（最大 700 m）、广度（长超过 580 km）以及缺氧底层水的长期分层确保了其良好的保存。多次分层，沉积物记录了具有区域意义的南半球气候信号。该赠款 1) 解决了下面提出的具体古气候问题，2) 在整个取芯区间完成了最初的岩芯描述。该研究将解决这些古气候问题：在过去的两次冰期间冰期周期中，这一南部热带环境在千年尺度上的有效水分、风和温度变化的方向、幅度和时间是什么？观察到的变化是否与热带海洋的海温变化或北大西洋温盐环流一致？马拉维的湖水位历史是怎样的？它与极地冰芯的甲烷记录（被解释为大陆热带湿度的全球平均测量值）相比如何？在马拉维湖和东非其他地区观察到的气候突变的证据是否与地球其他地区的已知事件（例如海因里希或丹斯加德/厄施格事件）一致？这些变化的方向、持续时间和幅度是什么？全球变暖早期时期的热带气候行为是什么（例如海洋同位素阶段 5e，或 MIS 11），这些时期开始和结束的突然程度如何？次要目标是完成最初的核心描述，包括勘察采样和过去 150 万年的低分辨率分析。更新世末期，南部热带地区的气候是否仅对低纬度岁差日照（23-19 kyr）的变化做出反应，或者也对高纬度冰量（100 kyr 和 41 kyr）强迫作出反应？ ？完成对这组独特样本的勘察、低分辨率分析，可以为更大的科学界服务，使其能够在未来对这些核心进行更精细的研究。采样和分析仅限于关键指标，重点是量化过去的有效湿度、灰尘和温度。代理分析在选定事件的时间间隔内以十年为单位进行，在更广泛的时间间隔内以千年为单位进行。这项研究的更广泛影响涉及气候对人类进化的作用，有助于解释构造历史东非裂谷的研究，并导致人们更好地了解气候对湖泊物种进化的控制。例如，马拉维的新记录以及其他非洲地点的记录表明，在约 75 公里之前有一段明显干旱的时期。这场干旱危机是否是该时期早期人口瓶颈的原因？该合作项目吸引了博士后、研究生和本科生的受训学者以及非洲同事，并涉及非洲和美国的外展部分。