Paleoclimatic research in tropical Africa relies heavily upon analysis of microfossils in lake sediment cores, and with these tools it has provided abundant evidence of dramatic fluctuations in equatorial temperatures, hydrology, and climatic seasonality since the Pleistocene. However, much of this work has suffered from several important limitations, among them (1) relatively coarse temporal resolution of microfossil series, (2) incomplete records due to erosion and/or discontinuous sedimentation, (3) difficulty in teasing out the relative contributions of past rainfall, winds, and other climatic factors to observed changes in the fossil record, and (4) difficulties in radiocarbon dating of cores, including ancient carbon reservoir effects and insufficient number of dates. These limitations have not only reduced the clarity of many paleoclimatic reconstructions; they often hinder comparisons between sites.
For this RUI proposal, the PI has subsampled a 9.9 m long sediment core from Lake Victoria, East Africa, at 2 cm intervals, and proposes to conduct a high-resolution analysis of the diatoms (single-celled algae with glass shells) preserved in those subsamples that will avoid the aforementioned limitations. The results of this project are likely to represent a significant contribution to our understanding of the history of, and forcing mechanisms behind, equatorial climates of the Holocene. The temporal detail will be unprecedented among tropical records of this length, yielding 16-18 year resolution over a span of roughly 9,000 14C years. Holocene sedimentation regimes in Lake Victoria have been remarkably uniform, so date interpolation for this record should be quite reliable. Because this core comes from an inshore site, it contains evidence of past lake level fluctuations (due to climatic changes) as represented by changes in the relative abundances of littoral diatoms. In addition, other fossil diatom taxa indicative of water column mixing regimes will yield a record of past fluctuations in monsoonal wind activity. From these unusually detailed diatom records, it should be possible to reconstruct a long and exceptionally detailed record of East African droughts, to gain insights into the role of short-term periodic climate oscillations in the tropics, to seek evidence of cyclic solar forcing of African climates, and to confirm the timing and nature of the abrupt climatic transition to greater tropical rainfall seasonality ca. 7200 years ago, as well as of the "Medieval Warm Period" and "Little Ice Age" interval which are still poorly documented in East Africa. The results of this study will be compared to other paleoclimatic datasets as well, including equatorial multi-proxy records and high-resolution polar ice core records, putting the climatic history of Lake Victoria into a global context.
