HOLOCENE LAKE LEVEL FLUCTUATIONS, SENECA LAKE, NEW YORK

Initial lake level compilations for North America by Harrison (1989) show that during the early to mid-Holocene, conditions were drier than present. More recent studies suggest a warm, wet climate persisted during the mid-Holocene in the eastern Great Lakes region, central New York State, and southern New England but was drier in the western Great Lakes region, central United States, and Ontario, Canada. Major changes in precipitation and runoff occurred throughout much of central New York State as shown by evidence for lake level fluctuations in three of the Finger Lakes in central New York State, Canandaigua, Cayuga and Owasco Lakes. Seneca Lake, the largest Finger Lake (by volume), is located near the transition between observed arid and wet conditions during the mid-Holocene. The focus of this project is to examine sediment grab samples and cores from Seneca Lake in order to document lake level changes over the last ~9,000 years by comparing spatial and temporal trends in sedimentation.

We examined a series of six sediment cores collected along an east-west transect in the northern end of Seneca Lake and twenty-five sediment grab samples collected along an east-west and north-south transect in the northern half of the lake in the summer of 2003. Cores were split, visually described, photographed, and sampled at 2 cm intervals. Sediment grab samples were obtained from the top 2 cm and homogenized. Samples were freeze-dried and then analyzed for weight percent total organic content and total calcium carbonate content by loss-on-ignition at 550°C and 1000°C respectively. Mineralogical analyses by X-ray diffraction provide semi-quantitative information about shifts in the source of the minerals in the lake sediment. Calcite abundance decreases and quartz, clay, and feldspar abundance increases in the sediment grab samples with increasing water depth and distance from the lakeshore. The relative abundance of minerals, the grain size distribution, and fossil content can be used to infer lake level fluctuations in the cores. The overall vertical succession of marginal lacustrine marls to laminated silts to marls to bioturbated silt indicates at least two small-amplitude relative rises and falls of lake level since ~7.4 ¹⁴ C ka.