Numerical modeling of subglacial sediment deformation: Implications for the behavior of the Lake Michigan Lobe, Laurentide Ice Sheet
Numerical modeling of subglacial sediment deformation: Implications for the behavior of the Lake Michigan Lobe, Laurentide Ice Sheet
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冰下沉积物变形的数值模拟：对劳伦泰德冰盖密歇根湖叶行为的影响
DOI：
10.1029/96jb00169
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发表时间：
1996
影响因子：
--
通讯作者：
J. C. Vela
中科院分区：
文献类型：
--
作者：
J. Jenson;D. Macayeal;P. Clark;C. Ho;J. C. Vela
我们应用一个威斯康星州晚期（约20，000年B. P.）密歇根湖叶（LML），劳伦泰德冰盖，研究如何细粒度的冰下沉积物可能会影响叶的行为，特别是在地质记录中观察到的快速千年尺度的边缘振荡。在加拿大地盾上方，我们假设一个刚性床（“硬层”）基底边界条件。在被细粒沉积物（“软层”）覆盖的地区，冰的底部与可变形的沉积物层耦合，使用速率依赖的应力应变定律。对LML沉积的富含粘土的冰碛物进行土工试验，以控制沉积物流变参数。模拟的横截面剖面与地质证据的重建是一致的。与时间相关的模拟表明，软层波瓣可能在大约20，000年或更短的时间内达到稳定状态，而其他相同的硬层波瓣则需要50，000至60，000年。沉积物粘度在实验确定的值的软层状叶约为两倍的响应千年尺度的变化，积累或消融作为一个非滑动的硬层状叶，但在这两种情况下，响应慢于地质记录所示。结果表明，虽然强大的千年尺度的变化积累和消融可以产生的反应，在硬层或软层的冰是符合地质记录，冰下沉积物粘度的变化，即使是相对温和的变化（无论是独立的或与气候变化），可能更容易占千年和submillennial-scale波动的叶缘。这些观察结果并不排除滑动的作用，但它们确实提供了一些视角，从这些视角来评估影响叶行为的各种过程的相对贡献。
We apply a numerical model of the late Wisconsin (circa 20,000 years B.P.) Lake Michigan Lobe (LML), Laurentide Ice Sheet, to investigate how fine-grained subglacial sediment might influence lobe behavior, particularly rapid millennial-scale marginal oscillations observed in the geologic record. Over the Canadian Shield, we assume a rigid bed (“hard bedded”) basal boundary condition. In areas overlain by fine-grained sediment (“soft bedded”), the base of the ice is coupled to a deformable sediment layer, using a rate-dependent stress-strain law. Geotechnical tests of clay-rich till deposited by the LML provide control for sediment rheologic parameters. Simulated cross-sectional profiles are consistent with reconstructions from geologic evidence. Time-dependent simulations suggest that a soft-bedded lobe could have reached steady state in about 20,000 years or less, in contrast to 50,000 to 60,000 years for an otherwise identical hard-bedded lobe. A soft-bedded lobe with sediment viscosity at the experimentally determined value is about twice as responsive to millennial-scale shifts in accumulation or ablation as a nonsliding hard-bedded lobe, but in both cases the response is slower than that indicated by the geologic record. Results suggest that while strong millennial-scale changes in accumulation and ablation can produce responses in hard-bedded or soft-bedded ice that are consistent with the geologic record, changes in subglacial sediment viscosity, even relatively modest changes (whether independent or in conjunction with climate change), might more readily account for millennial- and submillennial-scale fluctuations of the lobe margin. These observations do not exclude a role for sliding, but they do provide some perspective from which to evaluate relative contributions of the various processes that influence lobe behavior.