HR: 0800h
AN: PP21C-1594    [Abstracts]
TI: Mixing it Up: A Record of Holocene Climate Change in Non-Annually Laminated Sediment of Seneca Lake, NY
AU: * Rogers, C E
EM: rogers.caitlin@gmail.com
AF: Hobart and William Smith Colleges, Geoscience Department, Geneva, NY 14456
AU: Curtin, T M
EM: curtin@hws.edu
AF: Hobart and William Smith Colleges, Geoscience Department, Geneva, NY 14456
AB: The mid to late Holocene climate record was examined in two cores that represent distal sedimentation in Seneca Lake, one of 11 Finger Lakes in western New York. Laminated sediments, ~5 m thick, were collected from the middle of the lake at 131-137 m water depths. These sites were selected because they preserve a continuous record of changes in the hydrologic balance and sedimentary processes. Variations in grain size and fabric at 50-100-cm intervals were observed and represent time periods of hundreds to thousands of years. The combination of magnetic susceptibility, loss-on-ignition, grain size analysis by laser diffraction, and grain fabric analysis using thin sections allow us to reconstruct the evolution of the lake since deglaciation and to compare and contrast paleoclimate indicator data. Variations in the type of sedimentary fabrics preserved are coincident with variations in geochemical and sedimentological indicators of environmental conditions that may have occurred in response to fluctuations in the hydrologic balance and circulation and/or overturn. Laterally continuous, thin, black laminae rich in organic matter and possibly minute grains of iron sulfides accumulated during the mid Holocene Hypsithermal (~9-7 ka). Presence of black laminae may signify a steady supply of organic matter and an absence of oxygen, at least below the sediment-water interface if not in the lower part of the water column. Coincident with finely laminated sediment are the coarsest mean grain sizes. Three 2-6 cm thick sand beds occur in one core, suggesting that an influx of water and sediment occurred during intense storms. A combination of warmer surface water and influx of freshwater from storms during the Hypsithermal may have influenced the turnover history of the lake by stabilizing the water column. Absence of overturn would result in depletion of nutrients in surface waters, a decrease in primary productivity, and a decrease in oxygen at the bottom of the lake as a result of decaying organic matter. The presence of thicker, undisrupted black laminae (with iron sulfides) in both cores during this interval supports this hypothesis. Homogeneous, disrupted, or peloidal-rich laminae may have formed as a result of reworking by a combination of bottom currents and burrowing during the late Hypsithermal and Neoglacial (~7 ka-present). Cooler surface air temperatures and an associated southward shift in the jet stream likely changed the stratification history of the lake. If, during the winter months, the lake water circulates freely but stratifies during the summer, mixing of sediment may have occurred during the winter. Laminae would not be well-preserved in this scenario. Previous work shows that selective truncation of early Holocene sediment in shallower depths of Seneca Lake may reflect a change to dynamic atmospheric and lake circulation at during the end of the Hypsithermal and during the Neoglacial in response to cooler atmospheric temperatures and supports our working model for the degree of formation and preservation of laminae in Seneca Lake.
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