In situ Cosmogenic 10Be and 26Al in Deglacial Sediment Reveals Interglacial Exposure, Burial, and Limited Erosion Under the Quebec-Labrador Ice Dome

• Main Authors: Cavnar, Peyton M., Bierman, Paul R., Shakun, Jeremy D., Corbett, Lee B., LeBlanc, Danielle, Galford, Gillian L., Caffee, Marc
• Format: Text
• Language: English
• Published: 2024
• Subjects: Ice Sheet
• Online Access: https://doi.org/10.5194/egusphere-2024-2233; https://egusphere.copernicus.org/preprints/2024/egusphere-2024-2233/

To understand the erosivity of the eastern portion of the Laurentide Ice Sheet and the isotopic characteristics of the sediment it transported, we sampled buried sand from deglacial features (eskers and deltas) across eastern Canada (n = 10), a landscape repeatedly covered by the Quebec-Labrador Ice Dome. We measured concentrations of 10 Be and 26 Al in quartz isolated from the sediment and, after correcting for sub-surface cosmic-ray exposure after Holocene deglaciation, used these results to determine nuclide concentrations at the time the ice sheet deposited the sediment. To determine what percentage of sediment moving through streams and rivers currently draining the field area was derived from incision of thick glacial deposits as opposed to surface erosion, we used 10 Be and 26 Al as tracers by collecting and analyzing modern river sand sourced from Holocene-exposed landscapes (n = 11). We find that all ten deglacial sediment samples contain measurable concentrations of 10 Be and 26 Al equivalent on average to several thousand years of surface exposure – after correction, based on sampling depth, for Holocene nuclide production after deposition. Error-weighted averages (1 standard deviation errors) of measured 26 Al/ 10 Be ratios for both corrected deglacial (6.1 ± 1.2) and modern sediment samples (6.6 ± 0.5) are slightly lower than the production ratio at high latitudes (7.3 ± 0.3) implying burial and preferential decay of 26 Al, the shorter-lived nuclide. However, five deglacial samples collected closer to the center of the former Quebec-Labrador Ice Dome have much lower corrected 26 Al/ 10 Be ratios (5.2 ± 0.8) than five samples collected closer to the former ice margins (7.0 ± 0.7). Modern river sand contains on average about 1.75 times the concentration of both nuclides compared to deglacial sediment corrected for Holocene exposure. The ubiquitous presence of 10 Be and 26 Al in eastern Quebec deglacial sediment is consistent with many ...