Abstract

A series of 12 radiocarbon-dated sediment cores (up to 15 m long) were used to define the Holocene stratigraphy beneath the Cayuga Lake basin in central New York State in order to evaluate the stability of Holocene climate in the northeastern United States. These cores contain an abundance of thick lacustrine marls (> 30% CaCO 3 ) that were used to reconstruct century- to millennium-scale changes in lake levels and, thus, paleoclimates. The oldest sediments recovered (> 11.2 ka) consist of pink, proglacial clays that were deposited in Glacial Lake Iroquois between approximately 12.5 and 11.3 ka. Lacustrine sediment (non-marl) of Killarney-Younger Dryas age (11.2-10.3 ka) was recovered both north and south of modern Cayuga Lake, indicating relatively high lake levels during this well-known cold-climate phase. Following a brief (< 500 years) warm period immediately following the Younger Dryas, a relatively cool and dry climate persisted in the Finger Lakes region between < 9.8 and 8.5 ka correlative with global meltwater pulse IB. The Holocene Hypsithermal period ( approximately 9-4 ka) in the Cayuga Lake basin was characterized by widespread deposition of marl that locally contains as much as 90% CaCO 3 . These marls document a broad, first-order warming-cooling trend throughout the Hypsithermal, with the climatic optimum at approximately 7 ka. This long-term trend is consistent with insolation data as well as ice-core records from Greenland, and likely was a response to Milankovitch orbital forcing. Lake levels throughout the Finger Lakes region were relatively high during the Holocene Hypsithermal, implying an overall warm and wet climate in contrast to the traditional view of mid-Holocene drought. However, Hypsithermal climate and lake levels in the Finger Lakes region were not stable; rather they were characterized by significant century- to millennium-scale variability, implying short-term climate changes. Marl deposition in the Cayuga Lake basin ceased at approximately 3.4 ka when lake levels dropped as global cooling set in at the end of the Hypsithermal. However, there was a brief return to a warm and wet climate at approximately 1 ka, during the Medieval Warm Period prior to the onset of anthropogenic effects.

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