Measuring in situ Cosmogenic Beryllium-10 and Aluminum-26 in Deglacial Sediment Reveals Limited Erosion Under the Quebec-Labrador Ice Dome, Canada, 2022 - 2024

We know little about the Laurentide Ice Sheet’s erosive behavior prior to the Last Glacial Maximum because, as the ice sheet advanced, it largely eroded evidence of previous glaciations. To understand the erosivity of the eastern portion of the Laurentide Ice Sheet, the Quebec-Labrador Ice Dome, we sampled sand from deglacial features (eskers and deltas) across eastern Canada—a landscape repeatedly overrun by ice. We measured concentrations of 10Be and 26Al in quartz isolated from the sediment and, after correcting for cosmic-ray exposure during the Holocene, used these results to determine nuclide concentrations at the time of deglaciation. To infer sediment sourcing using Beryllium-10 (10Be) and Aluminum-26 (26Al), we collected and analyzed modern river sediment drained from Holocene-exposed landscapes.
The mean 10Be concentration in deglacial sediments (n=11) is (1.87 ±1.39) E4 atoms per gram (g-1) and (3.31 ±1.57) E4 atoms g-1 in modern river sediments (n=10). Corrected for Holocene exposure, we determined that deglacial sediment, at the time it was deposited by the ice sheet, contained between 7.60 E3 and 5.58 E4 atoms g-1 of 10Be inherited from prior periods of surface and near-surface exposure. 26Al/10Be ratios corrected for Holocene nuclide production range from 3.45 (- 2.26, +1.10) to 8.45 ± 4.19 in deglacial samples and 5.64 ± 0.78 to 7.92 ± 0.93 in modern river samples. Data suggest that, in eastern Quebec, sediment transported by modern rivers is derived in large part from glacial deposits, which may explain the similarity in nuclide concentrations between modern sediment and deglacial sediment (uncorrected). Our data also indicate that glacial erosion in eastern Canada was insufficient to remove cosmogenic nuclides produced during prior periods of exposure, implying that this portion of the Laurentide Ice Sheet was minimally erosive during the last glacial period. Most 26Al/10Be ratios for deglacial samples are near the production ratio for high latitudes, indicating that the landscape beneath the Quebec-Labrador Ice Dome went through multiple periods of Pleistocene interglacial exposure.