AN INITIAL INVESTIGATION OF REBOUND-DRIVEN LAKE LEVEL CHANGE IN SENECA LAKE, NY

Seneca Lake, one of the central New York Finger Lakes, is 4.8 km wide, 61.2 km long and about 186 m at its deepest. The purpose of this study was to begin to look for sedimentary evidence of lake level changes driven by regional isostatic rebound. We examined a series of 2 to 5.5 m long piston cores collected along a north-south transect in the lake. Cores were correlated using distinctive changes in the profiles of loss-on-ignition, magnetic susceptibility, grain size, and pollen. Carbonate concentrations are highest (30-37%) at the beginning of the Hypsithermal. Magnetic susceptibility values are highest during the beginning of the mid-Holocene and lower throughout the rest of the Holocene with only minor fluctuations. The coarsest mean grain sizes are coincident with the peaks in magnetic susceptibility during the beginning of the mid-Holocene Hypsithermal and during the late Neoglacial. We recognize a significant erosional unconformity of early to middle Holocene sediment at modern depths (<60m) because portions of the normal deep water sediment sequence were missing in the cores. At water depths >60m, we observe a complete sedimentary sequence. Based on radiocarbon dates and correlation using % carbonate, we hypothesize that the erosional surface formed between 9 and 6 ka.

Two additional cores were taken in the Catherine Creek Wetland Area south of the lake using a Russian peat borer. Maximum depth cored in the wetland was ~2.5m. The two cores were also analyzed for % carbonate and organic content, magnetic susceptibility, and pollen. These cores grade upwards from silty sand with less than 1% organic content and 5-10% carbonate to silt with approximately the same organic and carbonate content. Above ~1 m there is a transition to significant organic content. Organics exceed 20% while calcium carbonate becomes less than 5%. Wood was recovered from each core at ~1.7 m and will be used for radiocarbon dating. If post glacial isostatic rebound did drive lake level change we expect to see some evidence of transgression in the south end and the wetland without a corresponding level change near the outlet in the north. Isobase models suggest that there may have been sufficient rebound during the late Pleistocene – early Holocene, but we have not yet cored deep enough in the south end to observe this time interval.