Modelling present glacier dynamics on Svalbard - from inferringsurface velocities to computing a flow-consistent bedrock map

全球表面温度比上个世纪上升了约0.7摄氏度。由于高纬度地区气候变化的内在放大，气候变暖在极地地区表现得更明显。一个显著的后果是上个世纪观察到的斯瓦尔巴群岛冰川的普遍消退。在过去的几十年里，斯瓦尔巴群岛南部的冰川甚至以惊人的速度变薄。然而，这种最新的变薄趋势并未在整个北极得到证实。原因在于斯瓦尔巴群岛独特的气候条件。由于北大西洋温暖的洋流到达群岛的南端，气候相当温暖，纬度带也是多变的。因此，斯瓦尔巴群岛冰川的演变经常被认为是北极其他地区的先驱。在北极，斯瓦尔巴群岛在另一个方面是独一无二的，因为冰川范围和海拔变化在几十年里都有很好的特征。然而，从气候演变的角度来解释这些几何变化是受阻的，因为它们既来自气候表面质量平衡，也来自冰流散度。后者取决于冰川的几何形状和动态，不一定直接受气候参数变化的控制。然而，对冰川厚度和速度的观测是稀少的，在时间上不连贯，这阻碍了对斯瓦尔巴群岛冰川变化的动态控制的可靠量化。推而广之，我们对海洋冰锋的冰山崩解每年排放多少量也只有模糊的概念。冰的排放可能解释了总质量预算的很大一部分，因为超过一半的冰盖区域通过海洋终止的冰川排水。研究提案的目的是将关于冰川演变的冰动态组成部分的知识扩展到整个斯瓦尔巴群岛。为此，地面速度是从卫星遥感推断出来的，而卫星遥感反过来又有助于重建所有冰盖地区下的基岩地形。这种重建利用了质量守恒原理，因此提供了流动一致的厚度图，并已在我们的冰流模型中实现。关于冰速和冰层厚度的信息是量化冰流分歧的先决条件，这一分歧解释了迄今为止基本上未知的冰川变化部分。因此，根据观测到的北极大气变暖，重建将有可能更好地解释最近的几何变化。此外，以前对整个群岛的冰量和流量估计的外推可以在物理基础上得到改进。由于基岩重建与观测到的冰流一致，该图将为冰流模型在斯瓦尔巴群岛上的应用提供便利。通过我们的流动模型，我们的目的是推断底部滑动对现代冰川流动的贡献。

Global surface temperatures have risen by ~0.7°C over the previous century. Due to an inherent amplification of climatic changes in high latitudes, warming has been more expressed in Polar Regions. One eminent consequence is the general retreat of Svalbard glaciers observed throughout the last century. In the last decades, southern Svalbard glaciers have even moved on to thin at dramatically increasing rates. This latest thinning trend is however not confirmed throughout the Arctic. The reason relies in the unique climatic conditions on Svalbard. Since warm ocean currents in the North Atlantic reach the southern tip of the archipelago, the climate is rather warm and variable for its latitudinal band. Evolution of Svalbard glaciers has therefore often been suggested to play a precursor role for the other Arctic regions.Within the Arctic, Svalbard is unique in another respect, as glacier extents and elevation changes are well characterised over several decades. However, the interpretation of these geometric changes in terms of the climatic evolution is inhibited, as they arise from both the climatic surface mass balance and from ice flow divergence. The latter depends on glacier geometry and dynamics, and is not necessarily directly controlled by changes in climatological parameters. Yet, observations on glacier thicknesses and velocities are sparse and temporally incoherent, which impedes to this day a reliable quantification of the dynamic control on Svalbard glacier changes. By extension, we have only a vague idea on how much volume is annually discharged by iceberg calving at the marine ice fronts. Ice discharge presumably explains a large portion in the total mass budget, as more than half of the ice-covered area drains through marine-terminated glaciers.The aim of the research proposal is to expand the knowledge on the ice dynamic component of glacier evolution to the entire Svalbard archipelago. To this end, surface velocities are inferred from satellite remote sensing, which, in turn, serve to reconstruct the bedrock topography beneath all ice-covered areas. The reconstruction makes use of the mass conservation principle, provides therefore a flow-consistent thickness map and is already implemented in our ice flow model. Information on both ice velocities and ice thickness are a prerequisite to quantify the ice flow divergence that explains a, to this day, largely unknown portion of glacier changes. The reconstruction will therefore make it possible to better interpret recent geometric changes in the light of the observed atmospheric warming in the Arctic. Moreover, previous extrapolations for archipelago-wide estimates of ice volume and discharge can be improved on a physical basis. As the bedrock reconstruction is consistent with the observed ice flow, the map will facilitate the application of ice flow models on Svalbard. With our flow model, we aim at inferring the contribution of basal sliding to present glacier flow.