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.

目前我们对末次冰盛期（Last Glacial Maximum）之前劳伦泰德冰盖（Laurentide Ice Sheet）的侵蚀行为所知甚少，这是因为随着冰盖推进，其几乎完全剥蚀了此前冰川作用的证据。为了探究劳伦泰德冰盖东部区域——魁北克-拉布拉多冰穹（Quebec-Labrador Ice Dome）的侵蚀能力，我们在加拿大东部这片曾多次被冰盖覆盖的区域，从冰消期地貌（蛇形丘（eskers）与三角洲（deltas））的沉积物中采集砂样。我们对从沉积物中分离出的石英进行了10Be与26Al的浓度测定，并在校正全新世（Holocene）期间的宇宙射线暴露影响后，利用这些结果推算出冰消期时的核素浓度。为了通过铍-10（10Be）与铝-26（26Al）开展沉积物物源分析，我们还采集并分析了源自全新世暴露地貌的现代河流沉积物。
冰消期沉积物（样本量n=11）的10Be平均浓度为(1.87 ±1.39)×10⁴ 原子/克（g⁻¹），现代河流沉积物（n=10）的则为(3.31 ±1.57)×10⁴ 原子/克。经全新世暴露校正后，我们测得冰盖沉积形成该冰消期沉积物时，其中继承自此前地表及近地表暴露阶段的10Be浓度介于7.60×10³ 至5.58×10⁴ 原子/克之间。经全新世核素生成校正后，冰消期样本的26Al/10Be比值范围为3.45（-2.26，+1.10）至8.45 ±4.19，现代河流样本的则为5.64 ±0.78 至7.92 ±0.93。
数据表明，在魁北克东部区域，现代河流搬运的沉积物在很大程度上源自冰川沉积，这或可解释现代沉积物与未校正的冰消期沉积物之间核素浓度的相似性。我们的数据还显示，加拿大东部的冰川侵蚀作用不足以去除此前暴露阶段产生的宇宙成因核素，这意味着劳伦泰德冰盖的该区域在末次冰期期间的侵蚀程度极低。多数冰消期样本的26Al/10Be比值接近高纬度地区的核素生成比值，这表明魁北克-拉布拉多冰穹下方的地貌经历了多次更新世（Pleistocene）间冰期暴露阶段。