HIGH-RESOLUTION LATE QUATERNARY ISOTOPE RECORD IN WALDEN POND

A new high resolution CNS stable isotope and elemental proxy record from the deepest basin of Walden Pond, Massachusetts will be presented and interpreted in light of climate conditions from the late Pleistocene to present. The basal age of the core, 13.7ka BP was constrained by pollen data and 11 calibrated AMS ¹⁴C dates, and samples were taken every centimeter downcore, yielding an average temporal sampling resolution of 16.4 yr. Our proxy data suggest that Walden Pond is sensitive to regional and hemispheric climate events as well as more recent anthropogenic impact. Organic δ¹³C in this study indicates productivity, nutrient availability and organic matter sources, with more enriched δ¹³C indicating cooler and drier climate conditions. Bulk δ¹⁵N values may indicate nutrient sources and plant type, and bulk δ³⁴S data provide valuable information regarding anoxia and water column stratification, with more enriched values generally indicating increased mixing in the water column and less sulfate-reduction in the hypolimnion. The lower stratigraphy reveals a time of cold/dry climate, from ca. 13.8-11.7ka BP, corresponding with the well-documented Younger Dryas, 12.9-11.7ka BP. This is represented by decreases in organic matter input/productivity. Concentrations of sulfur, nitrogen, and organic carbon (OC) decreased significantly during this period. OC in the succeeding Greenlandian age ranged from 20.5% to 10.4% with an average of 14.3 ±1.9% to a range of 15.9% to 3.1% with an average of 6.5±2.9% during the YD and Middle Pleistocene. This climate shift is also indicated by depleted δ¹³C and δ¹⁵N, and decreased lake stratification as interpreted from enriched δ³⁴S in the YD. The YD event is further corroborated by analysis of pollen proxies, which show spruce-rich sediments associated with colder temperatures. The HCO is visible from 7-5ka BP, represented by slight increases in organic matter input and productivity and slightly enriched δ¹³C, as well as increased lake stratification as interpreted from significantly depleted δ³⁴S.The uppermost sediments record anthropogenic disturbance, with a visible shift in all isotopic proxies at 47 cal BP (ie 1903 CE). This new isotope record of Holocene regional climate variability and ongoing time-series analysis provides the opportunity to reconstruct multidecadal to millennial variability in the isotope record that will be beneficial to better understanding mid- to high-frequency regional climate variability over the Holocene Epoch.