A SEDIMENT RECORD OF MAJOR STORM EVENTS FROM KEUKA LAKE, NEW YORK

The record of climate and environmental change for northeastern North America during the Holocene is still poorly understood. We examined a ~5.9 cal ka record of storm events preserved in the laminated sediment of Keuka Lake, one of 11 Finger Lakes located in central-western New York. Keuka Lake has a steep surrounding hillslope, is very deep (maximum depth of 57 m), and has 12 major tributaries and numerous smaller streams that flow during snowmelt and heavy rainstorms. The core was recovered in deep water just offshore of an active stream (Boyd Point) in order to document the frequency of major storm events in the watershed. The core was described visually and analyzed for magnetic susceptibility, grain size, loss-on-ignition (weight percent water content, organic carbon and carbonate), and macroscopic charcoal abundance. In addition, three accelerator mass spectrometer radiocarbon dates of terrestrial plant macrofossils were analyzed and calibrated to calendar years using CALIB 5. An age-depth model was created assuming a constant sedimentation rate between successive radiocarbon ages. The core recovered diffusely laminated olive-gray and black hemipelagic to pelagic siliciclastic mud. Nine significant intervals were identified by cm-scale intervals of coarser mean grains size, high % sand content, and higher magnetic susceptibility. We suggest that these intervals result from high-energy fluvial transport events that produced sediment plumes in the lake and caused deposition of these sand-rich layers. These layers likely reflect multidecadal averaging of a series of large, recurring floods rather than a single event of long duration. Based on our age model, these events took place approximately every 500 yrs at: 5.8, 5.2, 4.7, 4.3, 3.8, 3.2, 2.6, 2.2, and 1.6 cal ka. The timing of these events in Keuka Lake are similar to those reported for large Mississippi River floods.