Mechanical tests of ice core samples from Dome GRIP, Greenland

为了了解大型极地冰块的流动行为，有必要研究天然冰川冰在深部的力学特性。由欧洲科学基金会资助的格陵兰冰芯项目于1990-1992年在格陵兰岛Dome GRIP(72ﾟ35‘N，37ﾟ38’W)成功获取了一个新的3029m深的冰芯。晶体在深度770米以下保持相当恒定的大小。威斯康星州冰(深度1624米以下)的晶体尺寸要小得多，这可能是由于较高的杂质浓度所致。在冰盖底部附近，晶体尺寸的增大可能是由于较高的冰温下晶体生长所致。晶体取向组构测量结果表明，单峰组构随着深度的增加而增强，尤其是在威斯康星州的冰层中出现了强烈的单峰模式。然而，在冰盖底部附近，组构形成多峰值模式，表明高温下冰晶重新结晶。单轴压缩试验中，应力轴与芯轴倾斜45ﾟ，以使最大分解剪应力平行于冰芯水平面。结果表明，冰很容易像晶体取向组构所预期的那样沿水平面变形。用各冰晶基面滑移的施密德因子对冰样的强度进行了定量解释。这些发现表明，圆顶可以很容易地通过基面水平的冰晶流动将位置调整到新的位置。

To understand the flow behavior of large polar ice masses, it is necessary to study the mechanical characteristics of natural glacier ice in the depth. A new 3029 m deep ice core was successfully obtained from Dome GRIP (72ﾟ 35'N, 37ﾟ38'W), Greenland by Greenland icecore Project sponsored by European Science Foundation during the 1990-92 field seasons.Crystal size measurements reveal characteristic changes with depth corresponding to changes of impurity contents and ice temperature. The crystals maintain fairly constant size below a depth of 770 m. Wisconsin ice (below adepth of 1624 m) shows much smaller crystal size probably due to the higher impurity concentrations. Near the bottom of the ice sheet, crystal size increases possibly resulted from crystal growth under the higher ice temperature.Results of crystal orientation fabrics measurements show strengthening of single maximum fabrics with depth, especially a strong single maximum pattern in Wisconsin ice. Near the bottom of the ice sheet, however, the fabrics becomes of multi-maximum pattern, suggesting recrystalization of ice crystals under a high temperature.Uniaxial compression tests was conducted with the stress axis inclined 45ﾟ from the core axis so as to have the maximum resolved shear stress parallel to the horizontal plane of the ice core. The results show that ice is quite easy to deform along the horizontal plane as expected from the crystal orientation fabrics. Quantitative interpretations on the strength of ice samples were made in terms of Schmid Factor for basal plane glide of each ice crystal. These findings suggest that the dome could easily adjust the position to a new location by the flow of ice crystals with basal plane horizontal.