Rapid southeastern Laurentide Ice Sheet thinning during the last deglaciation revealed by elevation profiles of in situ cosmogenic 10Be
Rapid southeastern Laurentide Ice Sheet thinning during the last deglaciation revealed by elevation profiles of in situ cosmogenic 10Be
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DOI：
10.1130/b36463.1
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发表时间：
2022-12
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通讯作者：
Christopher T. Halsted;P. Bierman;J. Shakun;P. Davis;L. Corbett;M. Caffee;Taylor S. Hodgdon;J. Licciardi
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作者：
Christopher T. Halsted;P. Bierman;J. Shakun;P. Davis;L. Corbett;M. Caffee;Taylor S. Hodgdon;J. Licciardi
末次盛冰期之后劳伦泰德冰盖体积变化的准确重建对于理解冰盖对海平面上升的贡献、融水对海洋环流的影响以及冰川消退的时空模式至关重要。在此，我们通过测量在美国东北部9座山的垂直剖面上采集的81个样本中的原地宇宙成因¹⁰Be，对末次冰川消退期间劳伦泰德冰盖的变薄情况提供了经验性约束。结合先前研究中5个垂直剖面上的107个暴露年龄样本，我们重建了冰盖变薄的历史。在边缘地点（距终碛200公里范围内），我们发现了在19.5千年到17.5千年之间约600米变薄的证据，这与纹泥记录所显示的初始边缘缓慢后退是一致的。在终碛以北400公里以上的地点，海拔1200米以上和以下的暴露年龄呈现出不同的模式。此海拔以上的年龄多变且更老，而在800 - 1000米海拔范围内较低海拔的年龄无法区分，这种模式表明在海拔约1200米处存在一个冰下热边界，将下方的侵蚀性、暖基冰与上方的多热、微侵蚀性冰分隔开来。来自上游山脉的低海拔年龄在15千年到13千年之间，这表明在波令 - 阿勒罗德暖期同时发生了约1000米的快速变薄。这些古冰快速变薄的速率与世界其他垂直暴露年龄剖面的速率相当，并且可能比现代南极和格陵兰全盆地的变薄速率更快，这表明劳伦泰德冰盖东南部对气候变暖高度敏感。
Accurate reconstruction of Laurentide Ice Sheet volume changes following the Last Glacial Maximum is critical for understanding ice sheet contribution to sea-level rise, the resulting influence of meltwater on oceanic circulation, and the spatial and temporal patterns of deglaciation. Here, we provide empirical constraints on Laurentide Ice Sheet thinning during the last deglaciation by measuring in situ cosmogenic 10Be in 81 samples collected along vertical transects of nine mountains in the northeastern United States. In conjunction with 107 exposure age samples over five vertical transects from previous studies, we reconstruct ice sheet thinning history. At peripheral sites (within 200 km of the terminal moraine), we find evidence for ∼600 m of thinning between 19.5 ka and 17.5 ka, which is coincident with the slow initial margin retreat indicated by varve records. At locations >400 km north of the terminal moraine, exposure ages above and below 1200 m a.s.l. exhibit different patterns. Ages above this elevation are variable and older, while lower elevation ages are indistinguishable over 800−1000 m elevation ranges, a pattern that suggests a subglacial thermal boundary at ∼1200 m a.s.l. separating erosive, warm-based ice below and polythermal, minimally erosive ice above. Low-elevation ages from up-ice mountains are between 15 ka and 13 ka, which suggests rapid thinning of ∼1000 m coincident with Bølling-Allerød warming. These rates of rapid paleo-ice thinning are comparable to those of other vertical exposure age transects around the world and may have been faster than modern basin-wide thinning rates in Antarctica and Greenland, which suggests that the southeastern Laurentide Ice Sheet was highly sensitive to a warming climate.