Northeastern Section - 53rd Annual Meeting - 2018

Paper No. 44-7
Presentation Time: 1:30 PM-5:30 PM


MAGDON, Irene, DUTIL, Mallory and GRIGG, Laurie D., Department of Earth and Environmental Sciences, Norwich University, 158 Harmon Dr., Northfield, VT 05663

Understanding climate variability during the last deglaciation contributes to our understanding of the feedbacks associated with a warming planet. In central Vermont and other parts of northern New England, paleoenvironmental records from lake and glacial sediments point to an unstable late-glacial climate. This study examines the fingerprint of a lake environment preserved in a sediment core from the Pecks Pond wetland in Barre, VT that extends from 8,000 to >14,500 yr BP. Loss-on-Ignition (LOI), grain-size, and macrofossil analyses indicate a shallow carbonate-rich lake occupied the basin for much of this time period. At the base of the core, low LOI values (5% CaCO3, 1% organic carbon), high percentages of sand-sized grains (20%), and limited macrofossils indicate high-erosion rates and low-productivity. At ca. 14,500 yr BP CaCO3 increases to 20%, sand-sized grains decrease to 10% and calcite encrustations and oospores of the macroalgae, Chara sp. increase suggesting a warmer and more productive lake which continues until 13,750 yr BP with the exception of one brief interruption at 14,100 yr BP where there is a reversal in these trends and an increase in the cold-water ostracode, Candona Candida. Between 13,750 and 13,600 yr BP there is a more significant decline in CaCO3, increased sand-sized grains and a peak in C. candida all of which suggest a colder lake environment. From 13,600 to 12, 750 yr BP CaCO3 and organic carbon increase to ca. 35 and 5%, while sand-sized grains and concentrations of C. Candida both decline. This data, in addition to the return of Chara macrofossils and a peak in the ostracode, Cypridopsis vidua, suggests that the lake became warmer and more productive during this time. At 12,750 yr BP a drastic and short-lived change in core stratigraphy from lake sediment to peat is matched by changes in LOI values, grain-size, and macrofossils and points to the development of a wetland. Shallow lake conditions return within 100 years and CaCO3 remain at ca. 35% until 11,250 yr BP which marks a transition to higher (45%) and more stable CaCO3 percentages. This record shows abundant paleoenvironmental variability that with further radiocarbon dating and macrofossil analysis will provide a much-needed record of climatic variability in northern New England during the late-glacial period.