Paper No. 3
Presentation Time: 8:00 AM-6:00 PM
HYDROGEN ISOTOPIC RESPONSES TO LATE PLEISTOCENE CLIMATE CHANGE IN LAKE MALAWI, AFRICA
KONECKY, Bronwen L., Geological Sciences, Brown University, Box 1846, Providence, RI 029012, RUSSELL, James M., Department of Earth, Environmental and Planetary Sciences, Brown University, Providence, RI 02912, JOHNSON, Thomas C., Large Lakes Observatory and Department of Geological Sciences, University of Minnesota Duluth, Duluth, MN 55812, BROWN, Erik T., Large Lakes Observatory & Dept of Geol. Sci, University of Minnesota Duluth, RLB-109, 10 University Drive, Duluth, MN 55812, BERKE, Melissa A., Large Lakes Observatory, Department of Geological Sciences, University of Minnesota Duluth, Duluth, MN 55812, WERNE, Josef P., Department of Geology & Planetary Science, University of Pittsburgh, Pittsburgh, PA 15260 and HUANG, Yongsong, Department of Geological Sciences, Brown University, 324 Brook Street, Providence, RI 02912, bronwen_konecky@brown.edu
Long-term droughts in tropical regions are often attributed to high latitude temperature changes and associated migrations of the Intertropical Convergence Zone (ITCZ). In Southeast Africa, paleoclimate records suggest a more complex climatology due to the additional influence of the African and Indian monsoon systems and zonal SST configurations in the Atlantic and Indian Oceans (Barker and Gasse, 2003; Tierney et. al, 2008). We present a new 140 kyr record of the Deuterium/Hydrogen ratio of terrestrial leaf waxes (δD
wax) from Lake Malawi, situated at the southernmost extent of the ITCZ over East Africa and adjacent to the boundary that divides the Indian and Atlantic Ocean monsoon systems. δD
wax is an indicator of variations in terrestrial hydrology through time, and application of this new tool to drill cores from Lake Malawi provides the longest high-resolution δD
wax record available from the region.
Our new record helps elucidate the patterns of paleoclimate evolution in Southeast Africa over the last glacial interval. Two distinct climate regimes dominated the Lake Malawi basin between 0-140 kyr BP. δDwax varies by up to 50‰ between 140-56 kyr BP, a time period characterized by a series of megadroughts documented across tropical Africa (Scholz et. al, 2007). Lake Malawi climate then transitions into a more stable regime, with δDwax varying by only 24‰ over the last 56 kyr. Isotopically depleted and enriched intervals last 2-3 kyr. The more recent patterns in δDwax do not follow the pattern of southern hemisphere summer insolation, suggesting that north-south migration of the ITCZ is not the only mechanism for isotopic anomalies associated with hydrological change at Lake Malawi.
Our record also provides critical insight into the δDwax proxy. A long-term trend towards D-enriched leaf waxes during a shift toward increasing or stable lake levels shows that local rainout amount is not the dominant control on δDwax variations at Lake Malawi, as has been previously proposed for tropical regions. Changes in moisture source region and transport history strongly influence δDwax, demonstrating the importance of constraining the climate signals embodied in tropical δDwax records with proxies for precipitation amount.
