NSF-NERC: Melting at Thwaites Grounding Zone and its Control on Sea Level (THWAITES-MELT)

该项目有助于美国国家科学基金会（NSF）和英国联合发起的联合倡议。自然环境研究理事会（NERC）将大幅改善对南极洲西部Thwaites冰川造成的冰损失和海平面上升的十年期和长期预测。西南极冰盖（WAIS）的命运是海平面变化预测中最大的不确定性之一。斯韦茨冰川（TG）是海平面上升的主要原因，其流动正在加速。这种更快的流动是对其变薄的浮冰架支撑作用减少的反应，最终是由海洋驱动的融化引起的。因此，代价高昂且具有地缘政治挑战性的海平面上升的程度在很大程度上取决于南极冰架下的冰-海相互作用。然而，Thwaites系统还没有得到充分的理解，暴露了我们对WAIS撤退，海洋驱动的强迫以及海平面后果的理解存在重大差距。 TG消退的主要调节器是其接地区的冰和海洋过程，该区域是从内陆流动的冰漂浮的位置。在这个精确的地点，冰和海洋的过程是我们理解海平面上升的核心，但关键变量并没有受到观测的限制。TG未来的模型预测显示出对接地区熔化的极端敏感性，以及如何应用熔化。同样可信的融化速率和地面区冰川学处理产生了西南极洲未来的不同轨迹，从变化不大到大规模冰盖崩溃，海平面上升半米或更多。结果的巨大不确定性源于在这一关键接地区缺乏观测。 对TG冰架融化的进一步了解将来自于该项目的重点观测计划，将被建立在最先进的冰盖和海洋耦合模型中。这些物理丰富，高分辨率的模式将使潜在的海平面的贡献TG被绑定到前所未有的程度。该项目将使全球和区域气候模拟，使未来的海洋条件的预测大陆架提供基于物理的预测TG的海平面的贡献，作出重大改进。该小组提出了一套综合活动：（1）TG冰架下的多年海洋学时间序列，以量化需要纳入海洋模型的融化过程，重点关注接地区，（2）对冰川进行类似测量，以验证控制接地线后退的过程，（3）将这些现场测量与新的高分辨率星载观测相结合，（4）将这种新的认识建立在最先进的海洋模式（麻省理工学院大气环流模式和帝国理工学院海洋模式）和冰盖模式（WAVI）中，以正确地模拟TG系统。（5）将这些模式耦合起来，并与现实的现代海洋强迫一起运行，以预测TG盆地未来百年的状况。国际团队将使用一系列技术，从成熟的技术，如使用热水钻来测量接地区的冰柱和水柱，到尖端技术，如部署钻孔部署远程操作车辆来调查接地区，以及使用相位相干雷达来监测冰应变和基础融化率。该项目的成果将是对TG系统在从接地线内陆几公里处延伸到冰架下的关键区域的更全面的了解。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估而被认为值得支持。

This project contributes to the joint initiative launched by the U.S. National Science Foundation (NSF) and the U.K. Natural Environment Research Council (NERC) to substantially improve decadal and longer-term projections of ice loss and sea-level rise originating from Thwaites Glacier in West Antarctica. The fate of the West Antarctic Ice Sheet (WAIS) is one of the largest uncertainties in projections of sea-level change. Thwaites Glacier (TG) is a primary contributor to sea-level rise and its flow is accelerating. This faster flow is a response to reduced buttressing from its thinning, floating ice shelf, and is ultimately caused by ocean-driven melting. The degree to which costly and geopolitically-challenging sea-level rise will occur therefore hangs to a large extent on ice-ocean interactions beneath such Antarctic ice shelves. However, the Thwaites system is not sufficiently well understood, exposing a significant gap in our understanding of WAIS retreat, its ocean-driven forcing, and the consequences for sea level. The chief regulators of TG's retreat are ice and ocean processes in its grounding zone, the location where the ice flowing from inland goes afloat. Ice and ocean processes at this precise locale are central to our understanding of sea-level rise, yet key variables have not been constrained by observation. Model projections of TG's future display extreme sensitivity to melting in the grounding zone and how that melting is applied. Equally-credible melt rates and grounding-zone glaciological treatments yield divergent trajectories for the future of West Antarctica, ranging from little change to large-scale ice sheet collapse with a half a meter or more of sea-level rise. The enormous uncertainty in outcome stems from the lack of observations in this critical grounding zone region. The enhanced understanding of melting of TG's ice shelf that will come from this project's focused observational program will be built into state-of-the-art coupled ice-sheet and ocean models. These physics-rich, high-resolution models will allow the potential sea-level contribution of TG to be bounded to an unprecedented degree.This project will enable global and regional climate modelers to make a substantial improvement to projections of future ocean conditions over the continental shelf by providing physics-based projections of TG's sea-level contribution. The team proposes a suite of integrated activities: (1) multi-year oceanographic time series from beneath TG's ice shelf to quantify melting processes that need inclusion in ocean models, with a strong focus on the grounding zone, (2) analogous measurements on the glacier to validate processes governing grounding-line retreat, (3) coupling of these in situ measurements with novel, high-resolution space-borne observations, (4) building this new understanding into state-of-the-art ocean (MIT General Circulation Model and Imperial College Ocean Model) and ice sheet (WAVI) models to correctly simulate the TG system, (5) coupling the models and running with realistic present-day ocean forcing to project the state of TG basin over the next hundred years. The international team will use a range of techniques, from the well-established, such as using a hot-water drill to instrument the ice column and water column in the grounding zone, through to the cutting-edge, such as deploying a borehole deployable remotely operated vehicle to survey the grounding zone, and using phase-coherent radar to monitor ice strain and basal melt rates. The outcome of the project will be a more complete understanding of the TG system in the critical zone extending from a few kilometers inland of the grounding line, through the grounding zone, and out under the ice shelf.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.