Of isbræ and ice streams
Of isbræ and ice streams
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伊斯布拉和冰流
DOI：
10.3189/172756403781816347
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发表时间：
2003
影响因子：
2.9
通讯作者：
K. Echelmeyer
中科院分区：
文献类型：
--
作者：
M. Truffer;K. Echelmeyer
快速流动的冰流和出口冰川为过去和现在冰盖的冰流提供了主要途径。这些冰流的移动速度比周围冰盖快100倍或更多。已经确定了几种快速冰流的机制，导致了一系列不同类型的冰流。在本文中，我们讨论了这一光谱的两个终端成员，我们将其称为“冰流”类型(由西南极的Siple海岸冰流表示)和“Isbræ”类型(由格陵兰岛的Jakobshavn Isbræ表示)。典型的冰流较宽，较浅(∼1000m)，地表坡度和驱动应力较低(∼10kpa)，冰流位置不受河床地形的强烈控制。快速流动是可能的，因为冰流有一个光滑的床，可能被微弱的、活跃变形的沉积物所覆盖。边缘剪切带很窄，支撑了大部分驱动应力，冰的变形几乎完全是横向剪切。冰川的边缘似乎天生就不稳定；它们会迁移，而且有看似合理的机制让这样的冰流关闭。Isbræ类型的冰流具有非常高的驱动应力，通常超过200 kpa。它们流经比周围冰层深得多的深基岩渠道，并具有陡峭的地表坡度。冰的变形既包括垂直切变，也包括横向切变，基面运动对整体运动的贡献不是很大。边缘剪切带相对于Isbræ宽度变得更宽，Isbræ及其边缘的位置强烈地受到基岩地形的控制。它们是稳定的特征，只有在邻近冰盖无法提供高冰通量的情况下才能关闭。伊斯布雷·S分布在格陵兰岛和东南极，可能还有西南极的松岛和斯韦茨冰川的部分地区。本文从冰川变形、冰底运动、冰下水文、冰流的季节性以及冰流的稳定性等方面对两种冰流进行了比较和对比。
Abstract Fast-flowing ice streams and outlet glaciers provide the major avenues for ice flow from past and present ice sheets. These ice streams move faster than the surrounding ice sheet by a factor of 100 or more. Several mechanisms for fast ice-stream flow have been identified, leading to a spectrum of different ice-stream types. In this paper we discuss the two end members of this spectrum, which we term the “ice-stream” type (represented by the Siple Coast ice streams in West Antarctica) and the “isbræ” type (represented by Jakobshavn Isbræ in Greenland). The typical ice stream is wide, relatively shallow (∼1000 m), has a low surface slope and driving stress (∼10 kPa), and ice-stream location is not strongly controlled by bed topography. Fast flow is possible because the ice stream has a slippery bed, possibly underlain by weak, actively deforming sediments. The marginal shear zones are narrow and support most of the driving stress, and the ice deforms almost exclusively by transverse shear. The margins seem to be inherently unstable; they migrate, and there are plausible mechanisms for such ice streams to shut down. The isbræ type of ice stream is characterized by very high driving stresses, often exceeding 200 kPa. They flow through deep bedrock channels that are significantly deeper than the surrounding ice, and have steep surface slopes. Ice deformation includes vertical as well as lateral shear, and basal motion need not contribute significantly to the overall motion. The marginal shear zone stend to be wide relative to the isbræ width, and the location of isbræ and its margins is strongly controlled by bedrock topography. They are stable features, and can only shut down if the high ice flux cannot be supplied from the adjacent ice sheet. Isbræs occur in Greenland and East Antarctica, and possibly parts of Pine Island and Thwaites Glaciers, West Antarctica. In this paper, we compare and contrast the two types of ice streams, addressing questions such as ice deformation, basal motion, subglacial hydrology, seasonality of ice flow, and stability of the ice streams.