Subglacial roughness of the Greenland Ice Sheet: relationship with contemporary ice velocity and geology
Subglacial roughness of the Greenland Ice Sheet: relationship with contemporary ice velocity and geology
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DOI：
10.5194/tc-13-3093-2019
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发表时间：
2019-05
期刊：
影响因子：
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通讯作者：
M. Cooper;Thomas M. Jordan;D. M. Schroeder;M. J. Siegert;Christopher N. Williams;J. Bamber
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文献类型：
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作者：
M. Cooper;Thomas M. Jordan;D. M. Schroeder;M. J. Siegert;Christopher N. Williams;J. Bamber
抽象的。格陵兰冰盖(GRIS)的冰下环境在其总体性质(例如地质、沉积物的存在和水的存在)以及界面条件(例如粗糙度和河床流变学)方面都受到很差的限制。因此，人们对空间不均匀的冰下特性如何与冰盖运动相关的了解有限。在这里，通过对20年无线电回波探测数据的分析，我们提出了一种新的系统分析GRIS下冰下粗糙度的方法。我们使用两种独立的方法来量化冰川下的粗糙度：第一，沿轨地形的可变性--通过与冰流垂直和平行排列的成对正交横断面来评估粗糙度各向异性；第二，根据床回波散射--能够评估精细尺度的河床特征。我们建立了冰下粗糙度的空间分布，并量化了其与冰流速度和方向的关系。总体而言，快速流动区域的河床被观察到比缓慢流动的内部更粗糙。在快速流动区，地形粗糙度与冰面速度呈指数标度关系，与流动方向平行但不垂直，各向异性程度与冰面速度相关。在许多缓慢流动的地区，两种粗糙度方法都显示了光滑床在空间上连贯的区域，结合下伏地质分析，我们得出结论，这可能是由于坚硬平坦床的存在。因此，这项研究为冰盖模型提供了空间可变的硬床或软床边界约束。
Abstract. The subglacial environment of the Greenland Ice Sheet (GrIS) is poorly constrained both in its bulk properties, for example geology, the presence of sediment, and the presence of water, and interfacial conditions, such as roughness and bed rheology. There is, therefore, limited understanding of how spatially heterogeneous subglacial properties relate to ice-sheet motion. Here, via analysis of 2 decades of radio-echo sounding data, we present a new systematic analysis of subglacial roughness beneath the GrIS. We use two independent methods to quantify subglacial roughness: first, the variability in along-track topography – enabling an assessment of roughness anisotropy from pairs of orthogonal transects aligned perpendicular and parallel to ice flow and, second, from bed-echo scattering – enabling assessment of fine-scale bed characteristics. We establish the spatial distribution of subglacial roughness and quantify its relationship with ice flow speed and direction. Overall, the beds of fast-flowing regions are observed to be rougher than the slow-flowing interior. Topographic roughness exhibits an exponential scaling relationship with ice surface velocity parallel, but not perpendicular, to flow direction in fast-flowing regions, and the degree of anisotropy is correlated with ice surface speed. In many slow-flowing regions both roughness methods indicate spatially coherent regions of smooth beds, which, through combination with analyses of underlying geology, we conclude is likely due to the presence of a hard flat bed. Consequently, the study provides scope for a spatially variable hard- or soft-bed boundary constraint for ice-sheet models.