A holistic model of outlet calving, dynamic acceleration and drawdown for the Greenland Ice Sheet

人类活动对全球气候产生重大影响的科学证据越来越多，公众的关切突出表明，需要更好地评估极地地区的当代环境变化。北半球最大的淡水储备量--相当于海平面上升7米--保存在格陵兰冰盖(GIS)内，但它现在和未来对海平面的贡献受到很大限制(IPCC，2007)。最近的观察表明，由于表面熔化增加(例如Steffen等人，2004年)和动态变薄(例如Rignot和Kanagaratnam，2006年)，地理信息系统边缘附近的质量损失正在加速。然而，控制内部下降的关键过程尚未完全确定，因此，没有纳入构成气专委海平面预测基础的冰盖模型。这在一定程度上反映了这样一个事实，即揭示冰川普遍加速的卫星数据不能以解决原因机制所需的时间分辨率获得。该项目的重点是西部地理信息系统的第二和第三大出口冰川，以帮助了解这些冰川通过冰山崩解加快速度并向海洋流失冰的过程。冰川崩解是一种机械破裂的过程，冰层从冰川和漂浮的冰架边缘断裂。它占了南极损失的大部分，占全球地理信息系统损失的50%以上。崩解是一种非常有效的质量损失机制，它提供了储存在陆地上的冰和海洋之间的快速连接，在那里它变成了海平面上升。尽管冰山崩解具有重要意义，但我们对冰山崩解的控制以及与之相关的动态下沉过程的了解很少，而且目前的耦合冰盖模式(ISMS)根本不能模拟这些过程，这严重阻碍了它们的预测能力。我们的目标是收集两个出口冰川的详细海洋、气候、大地测量和地球物理数据，这将使我们能够：1)调查控制冰山崩解的主要过程和联系及其对上游冰川流动和变薄的影响，2)利用这些数据完善新的基于过程的裂解/流动动力学标准，该标准可以很容易地包括在耦合模型中，以模拟未来的气候和极地冰盖及其对海平面上升的贡献。

The body of scientific evidence for significant anthropogenic impacts on the global climate is growing and public concern underscores a need for better assessments of contemporary environmental changes in polar regions. The greatest store of fresh water in the northern hemisphere - equivalent to 7m of eustatic sea level rise - is held within the Greenland Ice Sheet (GIS), and yet its present and future contribution to sea level is poorly constrained (IPCC, 2007). Recent observations suggest that mass loss near the margin of the GIS is accelerating through a combination of increased surface melting (e.g. Steffen et al, 2004) and dynamic thinning (e.g. Rignot and Kanagaratnam, 2006). However, the key processes controlling interior drawdown have yet to be fully identified, and in consequence, are not incorporated in the ice-sheet models which form the basis of the IPCC sea level projections. This in part reflects the fact that the satellite data that has revealed the widespread speed-up of glaciers cannot be acquired at the temporal resolution needed to resolve the causal mechanisms. This project focuses on second and third largest outlet glaciers of western GIS in order to help understand the processes by which these glaciers increase their speed and lose ice to the ocean by means of iceberg calving. Calving is the process of mechanical fracture where ice breaks off from the edge of glaciers and floating ice shelves. It accounts for the majority of loss from the Antarctic and over 50% of that from the GIS. Calving is a very efficient mass-loss mechanism which provides a rapid connection between the ice stored on land and the ocean where it is turned into sea level rise. Despite its fundamental importance, our understanding of the controls on iceberg calving and the associated process of dynamic drawdown are poorly understood and the present generation of coupled ice sheet models (ISMs) do not simulate these processes at all which severely handicaps their predictive ability. We aim to collect detailed oceanic, climatic, geodetic and geophysical datasets at two outlet glaciers which will enable us to: 1) investigate the main processes and linkages controlling iceberg calving and its effect on upstream glacier flow and thinning, and, 2) to use this data to refine a new process-based calving/flow dynamics criterion that can be easily included within models coupled to simulate the future climate and polar ice cover and its contribution on rising sea levels.