HR: 1340h
AN: PP33B-1570    [Abstracts]
TI: Reflections on Mud: Holocene Climate Variability Recorded by Laminated Sediments in Canandaigua Lake, NY
AU: * Morgan, C K
EM: clare.morgan@hws.edu
AF: Hobart and William Smith Colleges, Geoscience Department, Geneva, NY 14456 United States
AU: Curtin, T M
EM: curtin@hws.edu
AF: Hobart and William Smith Colleges, Geoscience Department, Geneva, NY 14456 United States
AU: Darden, W
EM: wadarden@amherst.edu
AF: Amherst College, Department of Geology, Amherst, MA 01002-5000 United States
AU: Halfman, J D
EM: halfman@hws.edu
AF: Hobart and William Smith Colleges, Geoscience Department, Geneva, NY 14456 United States
AU: Woodson, H
EM: hannah.woodson@trinity.edu
AF: Trinity University, Department of Geosciences, San Antonio, TX 78212 United States
AB: The Holocene sedimentary deposits in Canandaigua Lake, one of 11 Finger Lakes located in central New York, record evidence for environmental and climate change over the last ~14 ka. By analyzing high-resolution (2-12kHz) seismic reflection profiles and magnetic susceptibility, loss-on-ignition (LOI), grain size, and charcoal abundance of a sediment core collected from the profundal zone, temperature and precipitation variability is reconstructed. Seismic reflection profiles provide a three-dimensional view of sedimentation in the lake throughout the Holocene. The Holocene sequence ranges from 0 to ~10 m in thickness and is thickest in the middle of the lake, likely due to sediment focusing. The sequence contains several low amplitude, laterally continuous reflections that are traceable across the lake basin. Analysis of seismic reflection profiles allowed us to select a core site in an area with a relatively continuous, undisturbed record of Holocene sediment. A 4.71 m core was collected from 42°44.63' N, 77°19.69'W in the middle of the lake. Magnetic susceptibility was measured at a 1 cm interval prior to splitting the core. The core was opened, photographed, and described. Samples were collected at a 2 cm interval for LOI and grain size analysis, a 10 cm interval for charcoal analysis and smear slide examination, and at select intervals for thin section analysis. Preliminary data suggest that the low amplitude reflections observed in seismic reflection profiles are due to changes in density of the sediment that result from variations in grain size and packing. The core contains alternating dark gray and olive gray laminations that are often burrowed. Terrestrial organic material and ostracode shells are present throughout the core. Bulk magnetic susceptibility values range from 5 to 52 x 10^-6 SI. Fluctuations in susceptibility are greatest in the middle of the core. Concurrent high values (40-52 x 10^-6 SI) of magnetic susceptibility and mean grain size suggest a greater influx of water and terrestrial material to the lake during mid-Holocene storm events. Temperatures were likely warmest during the early to mid-Holocene in the Canandaigua Lake basin. Although the organic matter content is relatively similar (3-6%) throughout the Holocene, the carbonate content is greatest during the early to mid-Holocene. Higher carbonate concentrations are inferred to reflect warm surface water temperatures. Concurrent with the highest carbonate content values is the presence of laterally continuous, thin, black laminae rich in organic matter that accumulated during the early to mid-Holocene Hypsithermal (~9-5 ka). The presence of the black laminae indicates a steady supply of organic matter and very low to no oxygen in lake bottom water during accumulation of the organic- rich layer. The lake may have had occasional periods of thermal stratification during the summer and less frequent overturn during some parts of the Hypsithermal.
DE: 1845 Limnology (0458, 4239, 4942)
DE: 1861 Sedimentation (4863)
DE: 3344 Paleoclimatology (0473, 4900)
DE: 9350 North America
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005