LAKE-LEVEL RESPONSES TO ABRUPT CLIMATE CHANGES IN NORTH-CENTRAL PENNSYLVANIA SINCE >16 KA

Water levels in small lakes and ponds have widely responded to late-Quaternary climate changes, and we use a combination of geophysical surveys and sediment cores to reconstruct the hydrologic history of Sunfish Pond near Leroy, Pennsylvania (41°38'N 76°41'W). The small lake sits atop Barclay Mountain, a narrow ridge of the Appalachian Mountains near the southern limit of the Wisconsin glaciation. Ground-penetrating radar (GPR) profiles and a transect of three sediment cores indicate that the shoreline position of the lake has shifted over time with sandy littoral sediments extending outward into the lake stratigraphy, which is primarily composed of organic-rich muds. Calibrated radiocarbon ages from a sediment core collected in 2.25 m of water indicate that the lake formed by ca. 16.1 ka. Deposition of organic-rich muds in the near-shore core indicates moderately high water levels during the period of Heinrich Event 1, the Younger Dryas, and portions of the early Holocene. Sand layers and exceptionally low sediment accumulation rates indicate low water, however, from <16-12.5 ka and again from 5.5-2.8 ka. The water level has been near its modern high level since 2.8 ka based on extensive deposition of rapidly accumulating, organic-rich muds across the basin. The changes coincide with major changes in regional pollen records, and confirm the hydrologic significance of late-Pleistocene abrupt events in the Mid-Atlantic region.