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

自20世纪80年代以来，钻探东非裂谷的大型裂谷湖泊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7个钻孔中的两个地点(92%的回收率)采集了超过623米的岩心，其中包括600米水深中的一个洞，达到了380米的海底深度。该项目为北部盆地的一个高分辨率场地提供了三重岩心，该场地向后延伸了80 Kyr，为盆地中部覆盖过去200 Kyr的深部场地提供了双岩心，并为深层场地进行了单芯取心，深度为380米，其底部的年代为150万年。这些钻探岩芯是热带大陆现有的持续时间最长的高分辨率气候变化记录，它们有可能在整个岩芯长度范围内获得几十年/百年尺度的东非有效湿度和温度的高保真信号。马拉维湖位于东非裂谷(9S-14S)的南端，湖深(最大。700米长)、范围(超过580公里长)和缺氧底层水域的长期层结确保了沉积物保存完好，有时是层状的，记录了具有区域意义的南半球气候信号。这笔赠款1)解决了下面提出的具体古气候问题，2)完成了取芯间隔整个持续时间内的初始岩心描述。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，在千年尺度上，这个南部热带环境的有效湿度、风和温度的变化方向、大小和时间是什么？观测到的变化是否与热带海洋的海温变化一致，或与北大西洋温盐环流一致？马拉维的湖泊水位历史是怎样的？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衡量标准？观察到的马拉维湖和东非其他地区气候突然变化的证据是否与地球上其他区域的已知事件一致，例如海因里希事件或丹斯加德/奥施格事件？这些变化的方向、持续时间和幅度是什么？在全球变暖的早期阶段(如海洋同位素阶段5E或MIS11)，热带气候的行为是什么？这些阶段是如何突然开始和结束的？次要目标是完成最初的岩芯描述，包括过去150万年来低分辨率的勘察采样和分析。这个地处热带南部的地点的气候是只对低纬岁差日照(23-19KYR)的变化做出反应，还是也对更新世末期高纬度冰量(100KYR和41KYR)的强迫做出反应？完成勘测，对这组独特的样品进行低分辨率分析，为更大的科学界服务，使其能够在未来对这些岩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进行十年尺度，在更广泛的区间内进行千年尺度。这项研究的更广泛影响涉及气候对人类进化的作用，有助于解释东非裂谷的构造史，并导致更好地理解气候对湖泊物种进化的控制。例如，马拉维的新记录以及来自其他非洲遗址的记录表明，在~75KYR之前有一段明显的干旱时期。这场干旱危机是那个时期早期人口瓶颈的明显原因吗？这一合作项目吸引了博士后、研究生和本科生学者以及非洲同事参加，并涉及非洲和美国的外联部分。

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.