On the effects of anisotropic rheology on ice flow, internal structure, and the age-depth relationship at ice divides
On the effects of anisotropic rheology on ice flow, internal structure, and the age-depth relationship at ice divides
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各向异性流变学对冰流、内部结构和冰分界年龄深度关系的影响
DOI：
10.1029/2008jf001204
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发表时间：
2009
影响因子：
--
通讯作者：
O. Gagliardini
中科院分区：
文献类型：
--
作者：
C. Martín;G. Gudmundsson;H. Pritchard;O. Gagliardini
我们使用数值模拟与全系统斯托克斯求解器，以阐明非线性流变学和应变诱导的各向异性对冰流在冰鸿沟的影响。我们发现，各向异性流变学深刻地影响等时分层和表面形貌的形状。各向异性效应导致向下弯曲褶皱的形成，即，一个向斜，在冰分水岭下的较低中心区域的等时线中。当由此产生的向斜叠加在著名的雷蒙德背斜上时，就形成了双峰雷蒙德隆起。此外，在雷蒙德隆起的每一侧，形成侧翼向斜。此外，各向异性效应被发现引起一个微妙的表面轮廓的首脑会议的两侧。较低的中央向斜，侧翼向斜，和近山顶的表面斜坡都曾在自然界中观察到，但迄今为止没有解释这些特征的成因。我们将建模结果与从南极洲福克斯冰皮埃蒙特和基利冰隆收集的射线照片进行了比较。特别是，我们能够重现所有观察到的定性特征的表面几何形状和内部分层，包括，只有通过包括，诱导的非线性流变各向异性对流动的影响。流变各向异性有可能深刻地影响年龄分布与深度，和谨慎时，必须行使估计冰的年龄从冰芯与各向同性模型。在卫星图像中经常看到平行于冰分水岭脊的线状特征，这表明冰分水岭处于长期稳定状态，而不是像以前所认为的那样，有正在进行的冰分水岭迁移的迹象。这样的冰沟是提取冰芯的理想地点。
We use numerical modeling with a full-system Stokes solver to elucidate the effects of nonlinear rheology and strain-induced anisotropy on ice flow at ice divides. We find that anisotropic rheology profoundly affects the shape of both isochrone layering and surface topography. Anisotropic effects cause the formation of a downward curving fold, i.e., a syncline, in isochrones in the lower central area beneath the ice divide. When the resulting syncline is superimposed on the well-known Raymond anticline, a double-peaked Raymond bump is formed. Furthermore, to each side of the Raymond bump, flanking synclines are formed. In addition, anisotropic effects are found to give rise to a subtle concavity in the surface profile to both sides of the summit. The lower center syncline, the flanking synclines, and the near-summit surface concavity have all previously been observed in nature, but hitherto no explanation for the genesis of these features has been given. We compare modeling results with radiograms collected from Fuchs Ice Piedmont and Kealey Ice Rise, Antarctica. Good overall agreement is found. In particular, we are able to reproduce all observed qualitative features of surface geometry and internal layering by including, and only by including, the effects of induced nonlinear rheological anisotropy on flow. Rheological anisotropy has the potential to profoundly affect the age distribution with depth, and caution must be exercised when estimating age of ice from ice cores with an isotropic model. The occurrence of linear features parallel to the ridge of ice divides, often seen in satellite imagery, is indicative of long-term stability rather than signs of ongoing ice divide migration as previously suggested. Such ice divides are ideal locations for extracting ice cores.