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，钻探东非大裂谷的大型裂谷湖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7个孔中获得了超过623米的岩心（回收率为92%），其中一个洞位于600米深的水下，深达380米。该项目对盆地北部80kyr的高分辨率遗址进行了三核磁共振成像，对盆地中部200 kyr的深层遗址进行了双核磁共振成像，对380 m的深层遗址进行了单核磁共振成像，该基地的年代为150万年。这些岩心代表了热带大陆最长、连续的高分辨率气候变化记录，它们提供了在岩心长度上以几十年/几个世纪的尺度获得东非有效水分和温度的高保真信号的潜力。位于东非大裂谷（9S-14S）的南端，马拉维湖的深度(最大。700米的范围（超过580公里长）和长期的缺氧底水分层确保了保存完好的沉积物，有时是层状沉积物，记录了具有区域意义的南半球气候信号。该基金1)解决了下面提出的特定古气候问题，2)完成了在整个岩心区间内的初始岩心描述。这项研究将解决这些古气候问题：在过去的两个冰期-间冰期旋回中，在千年尺度上，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海温变率或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测量。马拉维湖和东非其他地区气候突变的观测证据是否与地球上其他地区的已知事件相吻合，例如海因里希事件或丹斯加德/奥斯格事件？这些变化的方向、持续时间和幅度是什么？在全球变暖的早期时期（例如海洋同位素阶段5e，或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？次要目标是完成最初的岩心描述，包括过去150万年的低分辨率侦察采样和分析。在更新世末期，南热带地区的气候是否只对低纬度岁差日晒（23-19千基尔）的变化有反应，还是对高纬度冰量（100千基尔和41千基尔）的强迫也有反应？完成对这组独特样品的侦察和低分辨率分析服务于更大的科学界，使其能够在未来对这些岩心进行更详细的研究。采样和分析仅限于关键代理，重点是量化过去的有效湿度，灰尘和温度。在选定事件的时间间隔内，在十年-世纪的尺度上进行代理分析，在更广泛的时间间隔内，在千年的尺度上进行代理分析。这项研究的更广泛影响是解决了气候在人类进化中的作用，有助于解释东非裂谷的构造历史，并有助于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~75年前有一段明显的干旱时期。在那个时期的证据中，是干旱危机导致了早期的人口瓶颈吗？这一合作项目包括博士后、研究生和本科阶段的培训学者，以及非洲同事，并包括在非洲和美国的外展部分

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.