60-54 Modern Problems Require Ancient Lakes: The Chronology and Chemistry of Glacial Lake Hitchcock

Session: 2YC and 4YCU Geoscience Student Research Poster Showcase

Presenting Author:

Authors:

Abstract:

Proglacial lakes and wetlands are sensitive environments that are and will continue to change in response to modern climate and cryosphere changes. Studying ancient proglacial lake systems, like Glacial Lake Hitchcock (GLH), provides an analog for understanding the climatic and hydrologic processes affecting modern glaciers and ice sheets.

Glacial Lake Hitchcock was a proglacial lake of the Laurentide Ice Sheet that occupied the Connecticut River Valley from 18.2-12.5 ka, during the Last Termination. Sediments deposited in GLH formed varves, which are well-documented and precisely calibrated as the basis of the North American Varve Chronology (NAVC). Carbonate concretions—formed in situ within these varved sediments—offer unique geochemical archives of the lake and groundwater environments. We studied these concretions in the context of their depositional setting to reconstruct the paleoclimatic and environmental evolution of GLH, a promising analog for modern proglacial environments. 

We collected concretions and sediment cores from five GLH field sites, spanning 4,000 years of GLH history (17.5–13.5 ka) and measured carbon and oxygen stable isotopes of the concretions.  The carbon isotope data was consistent with fractionation from an organic source, ranging between -17 and -9 ‰. Concretion δ¹⁸O spanned -4 to -11 ‰ (VPDB), which corresponds to inferred δ¹⁸O water values of -6 to -14 ‰  (VSMOW), assuming a water temperature of 3°C. Among a subset of concretion-hosting sites, δ¹⁸O scales along a North-South transect, accompanied by distinct changes in concretion morphology.  We interpret these changes to reflect either proximity to lower δ¹⁸O Laurentide meltwaters in more northerly settings or progressive northward concretion formation over time. We will present ongoing efforts to extract ostracod shells from GLH sediments and compare ostracod isotopic data with concretion data to test the relationship between lake waters and concretion-forming waters.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-9078

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