9632034 Krishnamurthy Except where historical data exist, proxy recorders provide the only functional means for retrieval of paleoenvironmental information The rapid sedimentation rates in lakes provide the potential to obtain continuous fine resolution records of environmental change on a regional scale. While some proxies, such as pollen, have been used successfully for a long time, others such as stable isotope ratios in inorganic carbonates are in a developmental stage. More proxies need to be developed because no single one can tell the entire story. This project will explore the potential of 13C, C/N and, especially, the D/H ratio of extractable organic matter in lake sediments from the Midwestern United States in the extraction of late glacial-Holocene climates of the region. In a pilot study using these proxies in the acid-resistant organic fraction extracted from Austin Lake (Kalamazoo, MI), it was shown that SW Michigan experienced a mid-Holocene warming (MHW) 8-3 kyrs BP. D/H provided the most dramatic evidence. This apparently is the first time D/H in organic matter in lake sediments has been measured for paleoclimate information. The strategy employed in this proposal is to make use of previously studied and archived cores obtained using mostly NSF funding (UMN, USGS, Bradford Institute of Oceanography) and to compare the results with records established by pollen studies. In addition,, some new sites that are currently being studied for palynology at the University of Minnesota will be studied for an integrated study using isotopic and pollen techniques: two with contrasting hydrologic settings in Kalamazoo, and two western Michigan sites. One of the western Michigan sites has already been cored by the UMN (separate NSF funding) in summer 1995. These latter sites are actively depositing carbonates and are deep enough to be laminated. Chronologies of the sediments, when not already established, will be by 14C and 210Pb techniques. The choice of arch ived cores from the Midwestern US insures (1) that minimal efforts and expenditure will be involved in field operations, (2) that advantage is taken of previous NSF funding for sample collection, and (3) that isotope techniques can be compared directly against the pollen-based documentation of the climate history of the region. This study will (1) test the preliminary findings that the D/H ratio of lake organic matter is a useful proxy of climate, and (2) provide a multi-proxy based continental, late Glacial-Holocene climatic history of the Midwestern United States. ??
