Linked and complex relationships of runoff from deglacial sedimentary systems to ocean basins likely contribute to the murky global signals of Heinrich Stadial 1 (ca. 17.5–14.5 cal. kyr B.P.). However, precise chronologies linking meltwater sources, transport, and oceanic sinks are lacking for this period. A probability density function of new and published radiocarbon dates shows Lake Chicago, a large meltwater lake adjacent to the Lake Michigan lobe of the Laurentide Ice Sheet, had two highstands, the Glenwood and Calumet phases, which occurred from ca. 17.0–15.0 cal. kyr B.P. and 14.0–12.4 cal. kyr B.P., respectively. Ages of the highest stands of Lake Chicago and high sediment accumulation rates at 16.5, 16.0, 15.1, 14.1, and 13.4 cal. kyr B.P. temporally correspond to large pulses of meltwater recorded in the δ18O values of Globigerinoides ruber (pink and white foraminifera) in sediment cores from the Orca Basin (Gulf of Mexico). We demonstrate overflow of meltwater via the Chicago outlet during highstands resulted in complex downstream responses, including burial of terrestrial plants in scoured alluvial channels, abandonment of riverine terraces, and coeval decreases in Gulf of Mexico stable oxygen isotope ratios.

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