Data_Sheet_1_On the Birth of Structural and Crystallographic Fabric Signals in Polar Snow: A Case Study From the EastGRIP Snowpack.zip

The role of near-surface snow processes for the formation of climate signals through densification into deep polar firn is still barely understood. To this end we have analyzed a shallow snow pit (0-3 meters) from EastGRIP (Greenland) and derived high-resolution profiles of different types of mechanically relevant fabric tensors. The structural fabric, which characterizes the anisotropic geometry of ice matrix and pore space, was obtained by X-ray tomography. The crystallographic fabric, which characterizes the anisotropic distribution of the c-axis (or optical axis) orientations of snow crystals, was obtained from automatic analysis of thin sections. The structural fabric profile unambiguously reveals the seasonal cycles at EastGRIP, as a consequence of temperature gradient metamorphism, and in contrast to featureless signals of parameters like density or specific surface area. The crystallographic fabric profile unambiguously reveals a signal of cluster-type texture already at shallow depth. We make use of order of magnitude estimates for the formation time of both fabric signals and discuss potential coupling effects in the context of snow and firn densification.

近地表雪过程在气候信号形成中的作用，尤其是在通过致密化进入深层极地雪垫的过程中，其作用机理仍处于初步理解阶段。为此，我们对来自东格陵兰（Greenland）的浅层雪坑（0-3米）进行了分析，并推导出不同类型机械相关结构张量的高分辨率剖面。通过X射线断层扫描获得了表征冰基质和孔隙空间各向异性几何形状的结构织构。通过自动分析薄片，获得了表征雪晶c轴（或光轴）方向各向异性分布的晶体织构。结构织构剖面明确揭示了东格陵兰的季节周期，这是由于温度梯度变质作用的结果，与密度或比表面积等参数的无特征信号形成鲜明对比。晶体织构剖面明确揭示了在浅层深度就已经存在的簇状纹理信号。我们利用结构张量和晶体织构形成时间的量级估计，并讨论了在雪和雪垫致密化过程中的潜在耦合效应。