Laurentide ice sheet thinning and erosive regimes at Mount Washington, New Hampshire, inferred from multiple cosmogenic nuclides
Laurentide ice sheet thinning and erosive regimes at Mount Washington, New Hampshire, inferred from multiple cosmogenic nuclides
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DOI：
10.1130/spe.s.13487109
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发表时间：
2020-10
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通讯作者：
Alexandria J. Koester;J. Shakun;P. Bierman;P. Davis;L. Corbett;B. Goehring;A. Vickers;S. Zimmerman
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作者：
Alexandria J. Koester;J. Shakun;P. Bierman;P. Davis;L. Corbett;B. Goehring;A. Vickers;S. Zimmerman
末次冰消期期间劳伦泰德冰盖在美国东北部低地向北退缩的历史已得到很好的确定，但由于缺乏对冰盖厚度在时间和空间上的直接限制，其垂直减薄历史却鲜为人知。此外，新英格兰的最高海拔地区以缓坡高地表面和风化岩块区域为特征，这些地貌的历史并不确定。为了更好地确定该地区冰盖历史及其与高山地貌的关系，我们在美国东北部最高峰华盛顿山（海拔1917米）沿一条海拔样带进行了20次新的铍 - 10和7次原位碳 - 14宇宙成因核素测量。我们的结果表明，该山上部和下部有着截然不同的暴露和侵蚀历史。在海拔1600米以上，铍 - 10和原位碳 - 14测量结果表明，该山上部在18000年前就已开始冰消。然而，一些铍 - 10年龄比末次冰消期的年龄大几倍，这与弱侵蚀性、冷基冰未对冰期前表面造成深度侵蚀的情况相符。在海拔1600米以下，铍 - 10年龄在近900米的海拔范围内无法区分，这意味着大约在14100 ± 1100年（1个标准差；n = 9）时冰面快速下降。这种从山上部冰消早期的缓慢减薄到低海拔地区的突然减薄的转变，与康涅狄格河谷纹泥记录所显示的在波令间冰段期间该地区冰缘加速后退的情况相吻合。华盛顿山宇宙成因核素垂直样带和康涅狄格河谷纹泥记录，以及新英格兰的其他宇宙成因核素记录都表明，在美国东北部内陆地区，由于波令暖期的影响，冰量迅速减少。
The northward retreat history of the Laurentide ice sheet through the lowlands of the northeastern United States during the last deglaciation is well constrained, but its vertical thinning history is less well known because of the lack of direct constraints on ice thickness through time and space. In addition, the highest elevations in New England are characterized by gently sloping upland surfaces and weathered block fields, features with an uncertain history. To better constrain ice-sheet history in this area and its relationship to alpine geomorphology, we present 20 new 10Be and seven in situ 14C cosmogenic nuclide measurements along an elevation transect at Mount Washington, New Hampshire, the highest mountain in the northeastern United States (1917 m above sea level [a.s.l.]). Our results suggest substantially different exposure and erosion histories on the upper and lower parts of the mountain. Above 1600 m a.s.l., 10Be and in situ 14C measurements are consistent with upper reaches of the mountain deglaciating by 18 ka. However, some 10Be ages are up to several times greater than the age of the last deglaciation, consistent with weakly erosive, cold-based ice that did not deeply erode preglacial surfaces. Below 1600 m a.s.l., 10Be ages are indistinguishable over a nearly 900 m range in elevation and imply rapid ice-surface lowering ca. 14.1 ± 1.1 ka (1 standard deviation; n = 9). This shift from slow thinning early in the deglaciation on the upper part of the mountain to abrupt thinning across the lower elevations coincided with accelerated ice-margin retreat through the region recorded by Connecticut River valley varve records during the Bølling interstadial. The Mount Washington cosmogenic nuclide vertical transect and the Connecticut River valley varve record, along with other New England cosmogenic nuclide records, suggest rapid ice-volume loss in the interior northeastern United States in response to Bølling warming.