NSFPLR-NERC: Melting at Thwaites grounding zone and its control on sea level (THWAITES-MELT)

西南极冰盖（WAIS）的命运是海平面上升预测中最大的不确定性之一。ThwaitesGlacier（TG）是海平面上升的主要原因，其流动正在加速。这种更快的流动是由于其变薄的浮动冰架的支撑作用减少，最终是由海洋融化造成的。因此，代价高昂且具有地缘政治挑战性的海平面上升将在很大程度上取决于南极冰架下的冰-海相互作用。然而，人们对Thwaites系统的了解还不够充分，这暴露了我们对WAIS退缩、其海洋驱动的强迫以及海平面后果的理解上的一个重大差距。TG退缩的主要调节因素是其接地区的冰和海洋过程，在那里，从内陆流来的冰漂浮在水面上。在这个精确的位置上的冰和海洋过程是我们理解海洋冰盖不稳定性的核心，但关键变量并没有受到观测的限制。这个问题是复杂的，因为海洋融化参考发生在深，狭窄的腔在接地区，在物理描述的过程驱动融化是未经证实的。这些知识的差距是有害的，因为模型预测TG的未来显示极端敏感的熔化在接地区和熔化是如何应用。同样可信的融化速率和接地区冰川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区域缺乏观测。该项目将观测、量化和模拟接地区的Thwaites冰-海洋系统，以牢固地建立海洋强迫和冰盖响应之间的物理联系。随时间变化的空腔将被彻底调查，并配备海洋监测设备。融化将由一个自主传感器网络和从太空观察一段时间。冰川的反应也将被观察到。我们对TG冰架下的融化、其接地区及其与冰川流的联系的进一步理解将被建立在最先进的冰盖和海洋耦合模型中。这些物理丰富的高分辨率模型将允许TG的潜在海平面贡献以前所未有的保真度为界。我们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，（2）对冰川的类似测量，以验证控制接地线后退的过程，（3）将这些现场测量与新的、高分辨率的空间遥感观测相结合，（4）将这种新的认识建立到最先进的海洋和冰盖模式中，以正确地模拟TG系统，（5）将这些模式与现实的现代海洋强迫相结合，以预测TG盆地在未来一百年的状态。国际团队将由经验丰富的海洋和冰川科学家组成，他们使用一系列技术，从成熟的到尖端的。该项目的成果将是彻底了解TG系统在关键区从几公里的接地线内陆延伸，通过接地区，并在冰架下。

The fate of the West Antarctic Ice Sheet (WAIS) is one of the largest uncertainty in projections of sea-level rise. ThwaitesGlacier (TG) is a primary contributor to sea-level rise and its flow is accelerating. This faster flow is a response to reducedbuttressing from its thinning, floating ice shelf, and is ultimately caused by ocean-driven melting. The degree to which costlyand geopolitically-challenging sea-level rise will occur therefore hangs to a large extent on ice-ocean interaction beneathAntarctic ice shelves. However, the Thwaites system is not sufficiently well understood, exposing a significant gap in ourunderstanding 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, where the ice flowing from inlandgoes afloat. Ice and ocean processes at this precise locale are central to our understanding of marine ice-sheet instability,yet key variables have not been constrained by observation. The problem is compounded because oceanic melt occurspreferentially in the deep, narrow cavity in the grounding zone, where physical descriptions of the processes driving melt are unverified.These gaps in knowledge are damaging because model projections of TG's future display extreme sensitivity to melting inthe grounding zone and how that melting is applied. Equally-credible melt rates and grounding-zone glaciologicaltreatments yield divergent trajectories for the future of West Antarctica, ranging from little change to large-scale ice sheetcollapse with a half a meter or more of sea-level rise. The enormous uncertainty in outcome stems from the lack ofobservations in this critical region.This project will observe, quantify and model the Thwaites ice-ocean system in the grounding zone, to firmly establish thephysics linking ocean forcing and ice-sheet response. The time-dependent cavity will be thoroughly surveyed andinstrumented with ocean monitoring devices. Melting will be observed by a network of autonomous sensors and from spaceover an extended period. The response of the glacier will also be observed. Our enhanced understanding of meltingbeneath TG's ice shelf, its grounding zone and its connection with the glacier flow will be built into state-of-the-art coupledice sheet and ocean models. These physics-rich, high-resolution models will allow the potential sea-level contribution of TGto be bounded with unprecedented fidelity.We propose a suite of integrated activities: (1) multi-year oceanographic time series from beneath TG's ice shelf to quantifymelting processes that need inclusion in ocean models, (2) analogous measurements on the glacier to validate processesgoverning grounding-line retreat, (3) coupling of these in situ measurements with novel, high-resolution space-borneobservations, (4) building this new understanding into state-of-the-art ocean and ice sheet models to correctly simulate theTG system, (5) coupling the models and running with realistic present-day ocean forcing to project the state of TG basinover the next hundred years . The international team will consist of experienced marine and glacier scientists using a rangeof techniques, from the well-established through to the cutting-edge. The outcome of the project will be a thoroughunderstanding of the TG system in the critical zone extending from a few kilometers inland of the grounding line, throughthe grounding zone, and out under the ice shelf.