Abstract Surface exposure dating with terrestrial cosmogenic nuclides (TCNs) has become the primary method for determining numerical ages of Pleistocene mountain glacial deposits and landforms in the conterminous western United States (U.S.) and in numerous other glaciated settings worldwide. Recent updates to models of TCN production and scaling warrant a reconsideration of published exposure ages of moraines of the last two Pleistocene glaciations and associated paleoclimate inferences. Previously reported TCN exposure ages of moraines are recalculated here using newer production rates and scaling models for nuclides helium-3 (3He), beryllium-10 (10Be), aluminum-26 (26Al), and chlorine-36 (36Cl), in most cases yielding significant differences from originally reported ages. Recalculated TCN exposure ages of moraines of the penultimate glaciation display a high degree of variability for individual landforms, particularly toward the younger end of age distributions, suggesting that exposure history is affected by moraine denudation and that older age modes provide the best estimate of the depositional age of these moraines. Oldest exposure ages of penultimate glaciation moraines are well-aligned among mountain ranges across the western U.S. and yield a mean of 138 ± 13 ka, indicating that mountain glaciation occurred in step with global ice volume maxima during marine oxygen isotope stage 6. On average, terminal moraines of the last glaciation date to 19.5 ± 2.3 ka and correspond to the latter part of the global Last Glacial Maximum (LGM). Down-valley recessional moraines representing prolonged glacial stabilizations or readvances to ≥75% of maximum lengths have a mean exposure age of 17.0 ± 1.8 ka, suggesting that these moraine positions were last occupied during Heinrich Stadial 1. Evidence for multiple glacial culminations during the last glaciation is found in several mountain ranges and likely reflects at least two phases of Late Pleistocene climate: an earlier phase when glaciers attained their maximum length in response to cooling during the LGM, and a later phase when glaciers persisted at or readvanced to near-maximum lengths in response to sustained cold temperatures and/or increased precipitation.

中文翻译：

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美国西部更新世山地冰川作用的更新宇宙成因年表和相关的古气候推断

摘要 用陆地宇宙成因核素 (TCN) 进行地表暴露测年已成为确定美国西部大陆 (US) 和全球许多其他冰川环境中更新世山地冰川沉积物和地貌数字年龄的主要方法。TCN 生产和缩放模型的最新更新需要重新考虑已公布的最近两次更新世冰川的冰碛暴露年龄和相关的古气候推断。先前报告的冰碛的 TCN 暴露年龄在这里使用更新的生产速率和比例模型重新计算，用于核素氦 3 (3He)、铍 10 (10Be)、铝 26 (26Al) 和氯 36 (36Cl)，在大多数情况下与最初报告的年龄产生显着差异的病例。重新计算的倒数第二次冰川冰碛的 TCN 暴露年龄显示出个体地貌的高度可变性，特别是在年龄分布的年轻末端，这表明暴露历史受到冰碛剥蚀的影响，并且较老的年龄模式提供了对沉积的最佳估计这些冰碛的年龄。倒数第二个冰川冰碛的最古老暴露年龄在美国西部的山脉中排列良好，平均为 138 ± 13 ka，表明在海洋氧同位素第 6 阶段，山地冰川与全球冰体积最大值同步发生。平均而言，最后一次冰期的终端冰碛日期为 19.5 ± 2.3 ka，对应于全球末次冰期最大值 (LGM) 的后期。