Technical Abstract:ACACIA addresses several key issues facing Quaternary geology, paleoclimatology, and limnogeology. The project hypotheses include 1) that whole-rock geochemistry of lake sediments is influenced by the composition and abundance of authigenic clays; 2) that the onset of aridity in East African lacustrine watersheds is reflected by enrichment in octahedral Mg content and oxygen isotopic compositions; 3) that octahedral Al enrichment reflects freshwater watershed flushing associated with the termination of arid phases; and 4) that environmental fluctuations reflect precession (Olduvai) and eccentricity (Olorgesailie) orbital influences thought to dominate at those times. ACACIA will sample and analyze sub-micrometer authigenic clay minerals and associated materials from well characterized stratigraphic sections in the Olduvai (Tanzania) and Olorgesailie (Kenya) Basins. To carry out this work we will partner with leading international field teams - Proyecto Olduvai at Olduvai Gorge (led by Universidad Complutense de Madrid), and the Olorgesailie Drilling Project at Olorgesailie (led by the Smithsonian Institution and the National Museums of Kenya). ACACIA mobilizes a team with extensive field experience in East Africa, along with analytical expertise in sedimentology, X-ray diffraction and fluorescence, high-resolution transmission electron microscopy, and silicate stable isotope geochemistry. These efforts will improve our understanding of the global climate system, tropical environmental responses to global climate change, changes in vertebrate and invertebrate ecosystem structure, and the evolution of the human lineage. ACACIA will support undergraduate research, enhance international collaborations, and partner with the only elementary school in the region near Olduvai Gorge, Tanzania, providing educational outreach and support to over 1000 Tanzanian K-8 students.Non-Technical Abstract:ACACIA will bring modern analytical approaches to bear on the question of how lake sediments record environmental changes in the past. Although scientists have previously used tools to reconstruct past environmental change such as the study of fossil pollen or plankton, many lakes have sediment accumulations that contain no fossils or other materials for reconstructing the ancient environment. For those cases in particular, ACACIA will develop the study of clay minerals, many of which chemically precipitate directly from lake water. We will sample from outcrops and cores in the Olduvai Gorge, Tanzania, and the Olorgesailie Basin, Kenya, which have well-dated volcanic ashes so we know the ages. From these lake sediment samples we will separate out particles that are smaller than 1/1000th of a millimeter, analyze their chemistry, and use electron microscopes to take pictures and analyze them. Based on those analyses, we will be able to infer when these ancient lakes contained fresh versus saline water, which is a strong indicator of when climate was humid versus arid in East Africa. Combined with other knowledge of environmental change in East Africa, this will give us important clues as to how tropical environments respond to global climate change, how African ecosystems have changed over the past few million years, and how the environments of early human evolution changed through time. This will also give us great insight into how microscopic clay particles interact chemically with lake water, which is important to the environments of lakes worldwide. ACACIA will support several undergraduate and graduate students, build international collaborations with Canadian, Spanish, Tanzanian, and Kenyan institutions, and conduct outreach to a Tanzanian elementary school with over 1000 students and few resources.
|Effective start/end date||6/1/14 → 5/31/17|
- National Science Foundation (National Science Foundation (NSF))