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: 0602404
• 负责人: Kristina Beuning
• 金额: $ 4.54万
• 依托单位: University of Wisconsin-Eau Claire
• 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 2009-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0602404&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，东非大裂谷的大型裂谷湖钻探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获得了超过623米的岩心（回收率92%），在七个孔中，包括一个在600米水中的孔，达到了380米的海底深度。该项目在北部盆地的一个高分辨率站点进行了三次取芯，该站点可追溯到80 kyr，在中央盆地的深层站点进行了两次取芯，覆盖了过去的200 kyr，并在深层站点进行了单次取芯，深度为380米，底部的日期为150万年。这些岩心代表了大陆热带地区最长的、连续的高分辨率气候变化记录，它们有可能在岩心长度上以几十年/几百年的尺度获得东非有效湿度和温度的高保真信号。马拉维湖位于东非大裂谷（9 S-14 S）的南端，马拉维湖的深度（最大深度）为100米。700米）、范围（超过580公里长）和缺氧底层沃茨的长期分层确保了保存完好，有时分层的沉积物记录了区域重要的南半球气候信号。该补助金1）解决下面提出的具体古气候问题，2）完成整个取芯间隔期间的初始岩心描述。这项研究将解决这些古气候问题：在过去的两个冰川间冰期周期中，在千年的尺度上，这个南部热带环境的有效水分，风和温度变化的方向，幅度和时间是什么？观测到的变化是否与热带海洋的SST变率或北大西洋温盐环流一致？马拉维湖平面的历史是怎样的？它与极地冰芯的甲烷记录相比如何？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？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上其他地区的已知事件相吻合，例如，Heinrich或Dansgaard/Oeschger事件？这些变化的方向、持续时间和幅度是什么？在全球变暖的早期（例如海洋同位素阶段5e，或者MIS 11），热带气候的行为是什么？这些时期的开始和结束有多突然？第二个目标是完成最初的岩心描述，包括过去150万年的低分辨率普查采样和分析。在更新世的最后一部分，南部热带地区这个地点的气候是否只对低纬度岁差日射（23-19 kyr）的变化作出反应，或者也对高纬度冰量（100 kyr和41 kyr）的强迫作出反应？完成对这组独特样本的勘察和低分辨率分析将为更大的科学界服务，使其能够在未来对这些核心进行更详细的研究。取样和分析仅限于关键的替代指标，重点是量化过去的有效湿度、灰尘和温度。代理分析进行了十年的世纪尺度的时间间隔的选定事件，并在千年尺度上的更广泛的intervation.The更广泛的影响，这项研究解决了气候对人类进化的作用，有助于解释构造历史的东非大裂谷，并导致更好地了解气候对湖泊物种进化的控制。例如，新的马拉维记录以及来自其他非洲遗址的记录表明，在约75 kyr之前有一段明显的干旱期。这场干旱危机是那个时期早期人口瓶颈的原因吗？这个合作项目吸引了博士后，研究生和本科生以及非洲同事的学者，并涉及非洲和美国的外展部分。