Measuring in situ 26Al and 10Be in Post-Glacial Sand Reveals Limited Erosion by Quebec-Labrador Ice Dome

• Main Author: Cavnar, Peyton McKinsey
• Format: Text
• Language: English
• Published: UVM ScholarWorks 2024
• Subjects: Cosmogenic; Ice Sheet; Isotope; Laurentide; Nuclides; Paleoclimate; Climate; Geochemistry; Canada
• Online Access: https://scholarworks.uvm.edu/graddis/1905; https://scholarworks.uvm.edu/context/graddis/article/2906/viewcontent/Cavnar_uvm_0243N_11686.pdf

There is minimal knowledge of the Laurentide Ice Sheet’s erosive behavior prior to the LastGlacial Maximum because, as the ice sheet advanced, it largely erased evidence of previous glaciations. Seeking 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) and from rivers across eastern Canada—a landscape repeatedly overrun by ice. We measured concentrations of 10Be and 26Al in quartz isolated from the sediment and, after considering cosmic-ray exposure during the Holocene, used the data to determine nuclide concentration at the time of deglaciation. The mean 10Be concentration in deglacial sediments (n=11) is 1.87 ±1.39*104 atoms g-1 and 3.31±1.57*104 atoms g-1 in modern sediments (n=10). Corrected for Holocene exposure, we determine that deglacial sediment, at the time it was deposited by the ice sheet, contained between 7.60*103 and 5.58*104 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. Our data indicate that glacial erosion in eastern Canada was insufficient to remove cosmogenic nuclides produced during prior periods of exposure. This provides further evidence that the Laurentide Ice Sheet was minimally erosive during the last glacial period, as studies on other portions of the ice sheet also show inherited nuclide concentrations preserved by limited erosion. Most 26Al/10Be ratios for deglacial samples are near the production rate for high latitudes, giving a strong indication that the Quebec-Labrador Ice Dome went through multiple periods of Pleistocene interglacial exposure.