Fabric along the NEEM ice core, Greenland, and its comparison with GRIP and NGRIP ice cores
Fabric along the NEEM ice core, Greenland, and its comparison with GRIP and NGRIP ice cores
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DOI：
10.5194/tc-8-1129-2014
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发表时间：
2014-07
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通讯作者：
M. Montagnat;N. Azuma;D. Dahl-Jensen;J. Eichler;S. Fujita;F. Gillet‐Chaulet;S. Kipfstuhl;D. Samyn;A. Svensson;I. Weikusat
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作者：
M. Montagnat;N. Azuma;D. Dahl-Jensen;J. Eichler;S. Fujita;F. Gillet‐Chaulet;S. Kipfstuhl;D. Samyn;A. Svensson;I. Weikusat
抽象的。结构（分布的晶体取向）沿着整个NEEM冰芯，格陵兰岛进行了测量，在现场的自动冰结构分析仪每10米，从33米到2461米的深度。织物从一个轻微的各向异性织物在顶部，朝着一个强大的单一最大值在约2300米，这是典型的变形模式主要是由单轴压缩和简单的剪切驱动。在全新世到威斯康星州（HW）的气候转变中，观察到组构强化率的急剧增加。从一个简单的模型，我们估计，这个深度位于从一个由垂直压缩为主的状态，以垂直剪切为主的状态的过渡。比较其他两个冰芯钻沿着同一脊; GRIP冰芯，钻在冰盖的首脑会议，和NGRIP冰芯，钻325公里的NNW的首脑会议沿着脊，和365公里的上游NEEM。这种比较倾向于表明，冰粘度的变化与HW气候转变必须与剪切为主的状态，诱导在NEEM观察到的突然织物加强。因此，这种比较反映了当沿沿着脊向西北方向从GRIP移动到NGRIP和NEEM时，剪切变形对取芯地点的作用越来越大。NEEM和NGRIP之间的组构剖面的差异也证明了NGRIP处与更尖锐的脊相关的更强的横向延伸。此外，沿着芯，在芯的底部观察到厘米尺度的突变纹理（织物和微观结构）变化。它们的位置与Dahl-Jensen等人（2013）中观察到的折叠层非常一致。
Abstract. Fabric (distribution of crystallographic orientations) along the full NEEM ice core, Greenland was measured in the field by an automatic ice texture analyzer every 10 m, from 33 m down to 2461 m depth. The fabric evolves from a slightly anisotropic fabric at the top, toward a strong single maximum at about 2300 m, which is typical of a deformation pattern mostly driven by uniaxial compression and simple shearing. A sharp increase in the fabric strengthening rate is observed at the Holocene to Wisconsin (HW) climatic transition. From a simple model we estimate that this depth is located at a transition from a state dominated by vertical compression to a state dominated by vertical shear. Comparisons are made to two others ice cores drilled along the same ridge; the GRIP ice core, drilled at the summit of the ice sheet, and the NGRIP ice core, drilled 325 km to the NNW of the summit along the ridge, and 365 km upstream from NEEM. This comparison tends to demonstrate that the ice viscosity change with the HW climatic transition must be associated with the shear-dominated state to induce the abrupt fabric strengthening observed at NEEM. This comparison therefore reflects the increasing role of shear deformation on the coring site when moving NW along the ridge from GRIP to NGRIP and NEEM. The difference in fabric profiles between NEEM and NGRIP also evidences a stronger lateral extension associated with a sharper ridge at NGRIP. Further along the core, centimeter scale abrupt texture (fabric and microstructure) variations are observed in the bottom part of the core. Their positions are in good agreement with the observed folding layers in Dahl-Jensen et al. (2013).