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

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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.