Vegetation and Climate of the African Tropics for the Last 500,000 Years

Abstract

In the last few decades, we have been witness to unprecedented changes in precipitation and temperature. Such alterations to our climate system have important implications for terrestrial ecosystems that billions of people depend on for their livelihood. The situation is especially tenuous for those living directly off the landscape via resources from natural ecosystems or subsistence agriculture as in much of tropical Africa. Studies of past climates provide potential analogues and help validate models essential for elucidating mechanisms that link changes in climate mean and variability and how they may affect ecosystem distribution and productivity. However, despite the importance of the paleo-record for insight into the future, tropical proxy records are rare, low resolution, and too short to capture important intervals that may act as analogs, such as the Last Interglacial (MIS 5e; ~130-115ka).Long, high-resolution drill cores from Lake Malawi, southeast Africa, provide a record of tropical climate and vegetation that extends back ~1.2mya, comprising many continuous glacial-interglacial cycles. My primary research involves conducting pollen analyses on these cores. First, I analyzed a high-resolution interval of the shortest Malawi core in order to better understand abrupt vegetation transitions during the Last Deglaciation. Further analysis was conducted on the longest Malawi core, beginning with an interval covering all of the Penultimate Glacial through the Last Interglacial. The resultant pollen data has shown that abrupt, large-scale landscape transitions from forest to desert follow local insolation and lake levels at the site, with a strong dependence of forest/woodland vegetation types on mean rainfall as well as rainfall seasonality. The interpretation of paleodata requires a good understanding of modern processes, thus another project has focused on using model simulations of the Last Interglacial and modern satellite NDVI time series to highlight dynamical and statistical relationships between vegetation and climate change. This work suggests that despite suggested links between monsoon intensity and SSTs in the southern African tropics, insolation controls on atmospheric circulation are the primary drivers of vegetation reorganization. In addition, this work highlights the importance of rainfall seasonality and dry season length in addition to precipitation controls on vegetation.