Thwaites Interdisciplinary Margin Evolution (TIME)

西南极冰盖（WAIS）包含200万立方公里的冰。全球科学界认为这是沿海环境和城市面临的最重大风险，因为它可能导致未来海平面上升。WAIS造成的风险加剧，因为它与变暖的海洋直接接触，其河床向内陆倾斜;后一个方面使冰容易受到广泛和长期的退缩。尽管科学家们从20世纪70年代初就已经意识到西南极洲冰系的不稳定性，但直到现在才变得明显，几个大型流域的冰流正在经历动态变化，这与长期的、可能无法阻止的解体的开始相一致，尽管不确定。当今科学界面临的两个基本的全球性挑战包括了解对WAIS稳定性的控制，以及通过改进冰流的计算机模拟来更准确地预测海平面上升。在TIME项目中，我们通过以下方式直接解决了这两个挑战：a）使用前沿技术观察快速变形的剪切边缘，假设剪切边缘对WAIS的Thwaites冰川出口的未来演变施加强有力的控制，和（b）利用观测记录，为尚未在用于预测WAIS对海平面上升的贡献的冰盖模型中实施的重要过程制定参数化。TIME将测试这是一个关键的假设，即通过思韦茨冰川排水盆地的冰流的未来演变是由其剪切边缘的动态控制的-冰川边缘的边界，通过该边界可以观察到冰流的增加。为了验证这一假设，研究小组将在思韦茨冰川东部剪切边缘的两个地点建立一个冰观测站。该团队认为，薄弱的地形控制使得这种剪切边缘容易向外迁移，并可能突然跳跃，以应对内陆冰的下降时，接地线的思韦茨撤退。冰观测站的设计目的是对重要的冰内特性进行新的全面限制，这些特性包括冰的变形率、冰晶结构、冰的粘度、冰的温度、冰的液态水含量和底部融化率。冰观测站还将确定基础条件，包括任何冰下沉积层和更深海洋沉积层的厚度和孔隙度。此外，该团队将开发新的知识，对冰流这些特性变化的后果给予前所未有的重视，包括对它们变化的空间和时间尺度的直接评估。这些知识将从三个实地地球物理平台获得：- 将使用无线地震检波器进行二维和三维主动震源地震调查，-宽带地震仪网络，以确定裂缝和基底滑动产生的冰震，-具有相控阵的自主雷达系统，可生成快速变形的内部层的连续3D图像，同时还可能揭示在河床处的基础水系统的几何形状。数据集将被纳入在不同空间尺度上开发的数值模型。一个将特别关注剪切边缘动力学，另一个剪切边缘动力学如何影响整个流域的冰流。该项目完成后，将确认思韦茨冰川的东部剪切边缘是否会像假设的那样迅速迁移，如果是的话，在本世纪及以后的海平面上升方面将产生什么影响。

The West Antarctic Ice Sheet (WAIS) contains 2 million cubic kilometers of ice. The global scientific community considers the it the most significant risk for coastal environments and cities, given its potential contribution to future sea-level rise. The risk posed by the WAIS is exacerbated because it is in direct contact with the warming ocean, and its bed slopes inland; this latter aspect makes the ice vulnerable to extensive and prolonged retreat. Although scientists have been aware of the precarious setting of the WAIS since the early 1970s, it is only now becoming apparent that the flow of ice in several large drainage basins is undergoing dynamic change, which is consistent with - although not certain to be - the beginning of a prolonged and potentially unstoppable disintegration. Two of the fundamental global challenges facing the scientific community today include understanding the controls on the stability of the WAIS, and enabling a more accurate prediction of sea-level rise through improved computer simulations of ice flow. In the TIME project, we directly address both challenges bya) using frontier technologies to observe rapidly deforming shear margins hypothesized to exert strong control on the future evolution of the Thwaites Glacier outlet of the WAIS, andb) using observational records to develop parameterizations for important processes which are not yet implemented in the ice sheet models used to predict the contribution of WAIS to sea level rise.TIME will test the key hypothesis that the future evolution of ice flow through the Thwaites Glacier Draining Basin is governed by the dynamics of its shear margin - the boundary at the edge of the glacier across which increased ice flow is observed. To test the hypothesis the team will set up an ice observatory at two sites on the eastern shear margin of Thwaites Glacier. The team argues that weak topographic control makes this shear margin susceptible to outward migration and, possibly, sudden jumps in response to the drawdown of inland ice when the grounding line of Thwaites retreats. The ice observatory is designed to produce new and comprehensive constraints on important englacial properties, which include ice deformation rates, ice crystal fabric, ice viscosity, ice temperature, ice liquid-water content and basal melt rates. The ice observatory will also establish basal conditions, including thickness and porosity of any subglacial sediment layer and the deeper marine sediments. Furthermore, the team will develop new knowledge with an unparalleled emphasis on the consequences of variations in these properties for ice flow, including a direct assessment of the spatial and temporal scales on which they vary. These knowledge will be obtained from three field-based geophysical platforms: - Active-source seismic surveys will be carried out in 2D and 3D, uniquely using wireless geophones, - A network of broadband seismometers, to identify the icequakes produced by crevassing and basal sliding, - Autonomous radar systems with phased arrays to produce sequential 3D images of rapidly deforming internal layers while potentially also revealing the geometry of a basal water system at the bed. Datasets will be incorporated into numerical models developed on different spatial scales. One will focus specifically on shear margin dynamics, the other on how shear margin dynamics can influence ice flow in the whole drainage basin. Upon completion, the project will have confirmed whether the eastern shear margin of Thwaites Glacier can migrate rapidly, as hypothesised, and if so what the impacts will be in terms of sea level rise in this century and beyond.