Thwaites Interdisciplinary Margin Evolution (TIME)

全球科学界认为，西南极冰盖对沿海环境和城市来说是最大的风险，因为它可能对未来海平面上升做出巨大贡献。WAIS构成的风险加剧了，因为它与变暖的海洋直接接触，而且其反向的海床坡度使冰层容易受到长期不稳定退缩的影响。尽管自1970年代初以来，科学家们就已经意识到WAIS的不稳定环境，但直到现在才变得明显的是，几个大型流域的冰流正在经历动态变化，这符合--尽管不一定是--持续的、可能无法阻止的崩解的开始。当今科学界面临的两个根本全球挑战包括了解对WAIS稳定性的控制，以及通过改进对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，我们直接应对这两个挑战：a)使用前沿技术观测快速变形的剪切边缘，假设这将对Thwaites冰川流域未来的冰流演变施加强有力的控制，以及b)使用观测记录为尚未在用于预测南极对海平面上升的贡献的冰盖模型中实施的重要过程开发参数。TIME将检验以下关键假设：通过Thwaites冰川流域的未来冰流演变是由将快速流动的冰川与周围缓慢移动的冰分开的剪切边缘的动态决定的。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。研究小组认为，地形控制的薄弱使得这一切变边缘很容易向外迁移，并可能在Thwaites冰川接地线后退时，因内陆冰的减少而突然跳跃。冰观测站的设计目的是对重要的冰川特性产生新的和全面的约束，这些特性包括冰变形速率、冰晶组构、冰粘度、冰温度、冰液态水含量和基本融化速率。冰观测站还将建立基本条件，包括任何冰下沉淀层和更深的海洋沉积物的厚度和孔隙度。此外，该小组将开发新的知识，无与伦比地强调这些特性的变化对冰流的影响，包括对它们变化的空间和时间尺度的直接评估。这些知识将来自跨学科的实地地球物理平台，包括三维有源地震勘探、二维有源地震断面、全球定位系统网络和互补的无源宽带地震仪网络，以及部署相控阵以探测冰和床中迅速变形的内层和液态水的自主雷达系统。数据集将被纳入在不同空间尺度上开发的数值模型中。其中一个将专门关注剪切边缘动力学，另一个将专注于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Thwaites冰川的东部剪切边缘是否可以如假设的那样迅速迁移，如果是的话，将对本世纪及以后的海平面上升产生什么影响。

The global scientific community considers the West Antarctic Ice Sheet to be the most significant risk for coastal environments and cities, given its potentially large 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 because its reverse bed slope makes the ice vulnerable to a prolonged unstable 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 sustained 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 by:a) using frontier technologies to observe rapidly deforming shear margins hypothesized to exert strong control on the future evolution of ice flow in the Thwaites Glacier drainage basin, andb) using observational records to develop parameterisations for important processes which are yet to be implemented in the ice sheet models used to predict the Antarctic contribution to sea level rise.TIME will test the key hypothesis that the future evolution of ice flow through the Thwaites Glacier drainage basin is governed by the dynamics of the shear margins that separate the fast flowing glacier from the slow-moving ice that surrounds it. 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 Glacier 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 interdisciplinary field-based geophysical platforms, including 3D active-source seismic surveys, 2D active-source seismic transects, networks of GPS and complementary passive broadband seismometers, and autonomous radar systems deployed with phased arrays to detect rapidly deforming internal layers and liquid water in the ice and 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.