Thwaites Interdisciplinary Margin Evolution (TIME)

南极西部冰盖（WAIS）包含200万立方千米的冰。全球科学界认为，考虑到它对未来海平面上升的潜在影响，它是沿海环境和城市面临的最大风险。由于与变暖的海洋直接接触，其海床向内陆倾斜，西海带带来的风险更加严重；后一种情况使冰容易受到大范围和长时间的退缩。尽管科学家们早在20世纪70年代初就已经意识到WAIS的危险环境，但直到现在才变得明显，几个大流域的冰流正在发生动态变化，这与——尽管不确定——长期的、可能不可阻挡的解体的开始是一致的。当今科学界面临的两个基本的全球挑战包括了解对WAIS稳定性的控制，以及通过改进的冰流计算机模拟来更准确地预测海平面上升。在TIME项目中，我们直接解决了这两个挑战：a)使用前沿技术观测快速变形的剪切边缘，这些剪切边缘被假设对WAIS的Thwaites冰川出口的未来演变施加强烈控制；b)使用观测记录开发重要过程的参数化，这些过程尚未在用于预测WAIS对海平面上升贡献的冰盖模式中实现。《时代》杂志将检验一个关键假设，即通过斯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力学控制的——在冰川边缘的边界上，观察到冰流的增加。为了验证这一假设，研究小组将在斯韦茨冰川东部剪切边缘的两个地点建立一个冰观测站。研究小组认为，薄弱的地形控制使得这个剪切边缘容易受到向外迁移的影响，而且当斯韦茨的接地线后退时，可能会随着内陆冰的减少而突然跳跃。冰天文台的设计目的是对重要的冰川特性，包括冰的变形速率、冰晶结构、冰的粘度、冰的温度、冰的液态水含量和基本融化速率，产生新的和全面的约束。冰观测站还将建立基础条件，包括任何冰下沉积物层和更深的海洋沉积物的厚度和孔隙度。此外，该团队将开发新的知识，无与伦比地强调这些特性变化对冰流的影响，包括对它们变化的时空尺度的直接评估。这些知识将从三个基于现场的地球物理平台获得：—主动震源地震调查将以2D和3D的方式进行，独特地使用无线检波器；—宽带地震检波器网络，用于识别裂缝和基底滑动产生的冰震；—具有相控阵的自主雷达系统，用于生成快速变形的内层的连续3D图像，同时也可能揭示基底水系统的几何形状。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，另一个将关注剪切边缘动力学如何影响整个流域的冰流。项目完成后，将确认斯韦茨冰川的东部剪切边缘是否能像假设的那样快速迁移，如果是这样，将对本世纪及以后的海平面上升产生什么影响。

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.