A 350,000 - Year History of Rainfall and Temperature in Tropical East Africa

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).

This award supports analyses of two cores recovered in 2005 from the floor of Lake Malawi, in Africa. These cores contain approximately 350,000 years of temperature and rainfall proxies from the central basin of Lake Malawi. Initial results from the Lake Malawi Drilling Project have thus far provided: (1) surprising new insights into the recurrence and intensity of drought in East Africa for the past 150,000 years, (2) a preliminary estimate of past lake ecosystem dynamics, (3) compelling evidence for a tie between the climate in this part of the African tropics with the bipolar see-saw, and (4) a thermal history of the region that extends back 75,000 years.

This project addresses the following questions: 1. To what extent do temperature and rainfall follow insolation forcing of either hemisphere? 2. What is the relationship between temperature and humidity shifts in the Malawi basin and concentrations of atmospheric CO2 and CH4? 3. What is the nature of millennial-scale variation in temperature and rainfall in the Malawi basin over the past ~500,000 years? 4. To what extent do temperature and rainfall in the Malawi basin respond to the sea-surface temperature regime of the tropical Pacific and Indian Oceans?

The project obtains estimates of past rainfall from analyses of the del-D record derived from long-chain fatty acids and of the del-13C record preserved in the long-chain n-alkanes of terrestrial vegetation preserved in Lake Malawi sediment. Estimates of past temperature are based on a paleotemperature proxy for the marine environment called TEX86. This approach has provided promising results from previous work on both Lake Malawi and Lake Tanganyika in East Africa. The group continues to improve on the age model of the long Malawi drill core, focusing on U/Th dating of carbonate nodules that are found at a few, carbonate-rich intervals in the core. These dates are supplemented with precessional tuning of the carbonate abundance record.

The climate history of tropical Africa portends a future of recurring severe and long-lasting drought that will have enormous impact on human welfare in the region. The data that will be provided from this research will be invaluable for comparison to marine sediment and speleothem records from the tropics that span the past few hundred thousand years, and for testing the accuracy of climate models that are necessary to improve long-term weather forecasts for this heavily populated portion of the African continent. The project involves graduate and undergraduate students in laboratory analyses and in all aspects of interpretation and dissemination of results, through graduate thesis research and undergraduate research opportunities.