Abstract
We report previously unpublished evidence for a Marine Isotope Stage 3 (MIS 3; 60–26 ka) glacial outburst flood in the Torngat Mountains (northern Quebec/Labrador, Canada). We present 10Be cosmogenic exposure ages from legacy fieldwork for a glacial lake shoreline with evidence for outburst flooding in the Torngat Mountains, with a minimum age of 36 ± 3 ka (we consider the most likely age, corrected for burial, to be ~56 ± 3 ka). This shoreline position and age can potentially constrain the Laurentide Ice Sheet margin in the Torngat Mountains. This region, considered a site of glacial inception, has no published dated geologic constraints for high-elevation MIS 3 ice margins. We estimate the freshwater flux associated with the inferred glacial outburst flood using high-resolution digital elevation maps corrected for glacial isostatic adjustment. Using assumptions about the ice-dammed locations we find that a freshwater flood volume of 1.14 × 1012 m3 could have entered the Hudson Strait. This glacial outburst flood volume could have contributed to surface ocean freshening to cause a measurable meltwater signal in δ18O records, but would not necessarily have been associated with substantial ice rafted debris. Future work is required to refine estimates of the size and timing of such a glacial outburst flood. Nevertheless, we outline testable hypotheses about the Laurentide Ice Sheet and glacial outburst floods, including possible implications for Heinrich events and glacial inception in North America, that can be assessed with additional fieldwork and cosmogenic measurements.
Highlights
States around this time (~38 ka; Karig and Miller, 2013). These datasets suggest either a rapidly advancing ice sheet from a Hudson Bay ice dome or a substantially revised ice sheet arrangement that entails many separate ice caps. Building on this observational evidence, glacial isostatic adjustment (GIA) analysis using anomalously high sea-level markers along the United States mid-Atlantic dated to 50-35 ka supports a late and rapid eastern Laurentide glaciation, suggesting that Laurentide ice volumes increased four-fold from mid-Marine Isotope Stage 3 (MIS 3) to the LGM (Figure 1D; Pico et al, 2017)
We explore possible implications for MIS 3 Heinrich events by calculating the freshwater flux associated with such a glacial outburst flood using high-resolution digital elevation maps corrected for glacial isostatic adjustment
In this study we provide the first direct on-land evidence for an MIS 3 glacial outburst flood
Summary
Millennial-scale climate oscillations in the Northern Hemisphere are prominent features of Marine Isotope Stage 3 (MIS 3; 60-26 ka). These datasets suggest either a rapidly advancing ice sheet from a Hudson Bay ice dome or a substantially revised ice sheet arrangement that entails many separate ice caps Building on this observational evidence, glacial isostatic adjustment (GIA) analysis using anomalously high sea-level markers along the United States mid-Atlantic dated to 50-35 ka supports a late and rapid eastern Laurentide glaciation, suggesting that Laurentide ice volumes increased four-fold from mid-MIS 3 to the LGM (Figure 1D; Pico et al, 2017). We report previously unpublished data from legacy fieldwork suggesting an MIS 3 glacial lake and outburst flood in the Torngat Mountains (pre-LGM glacial lake Koroc, Figure 3) This evidence, including 10Be ages on a wave-cut shoreline, puts forth a series of testable hypotheses about MIS 3 Laurentide configuration and Heinrich events. White circle shows location age is measured on lake shoreline
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