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

南极西部冰盖（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。这种更快的流动是对变薄的浮冰架支撑减少的反应，最终是由海洋驱动的融化造成的。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，对斯韦茨系统的了解还不够充分，这暴露了我们对斯韦茨退缩、其海洋驱动的强迫作用以及对海平面的影响的理解存在重大差距。TG撤退的主要调节者是其搁浅区的冰和海洋过程，在那里，从内陆流出的冰漂浮在海面上。这个精确地点的冰和海洋过程是我们了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。这个问题更加复杂，因为海洋融化主要发生在接地带深处狭窄的空腔中，在那里，驱动融化过程的物理描述尚未得到证实。这些知识上的差距是有害的，因为TG未来的模型预测显示出对接地区融化以及如何融化的极端敏感性。同样可信的融化速度和接地带冰川学处理方法为西南极洲的未来提供了不同的轨迹，从微小的变化到大规模的冰盖崩塌，海平面上升半米或更多。结果的巨大不确定性源于对这一关键区域缺乏观察。该项目将在搁浅区观察、量化和模拟斯韦茨冰海系统，以牢固地建立海洋强迫和冰盖响应之间的物理联系。将对这个随时间变化的空腔进行彻底调查，并配备海洋监测设备。一个由自主传感器组成的网络将在很长一段时间内从太空观测冰层的融化情况。冰川的反应也将被观察到。我们对TG冰架下的融化，其接地带及其与冰川流的联系的进一步了解将建立在最先进的耦合片和海洋模型中。这些富含物理学的高分辨率模型将使tga对海平面的潜在贡献具有前所未有的保真度。我们提出了一套综合活动：(1)从TG冰架下的多年海洋时间序列来量化需要包含在海洋模型中的融化过程；(2)冰川的类似测量以验证控制接地线退缩的过程；(3)将这些原位测量与新颖的高分辨率空间观测相结合；(4)将这种新的理解建立在最先进的海洋和冰盖模型中，以正确模拟TG系统；(5)将模型与当前海洋强迫相结合，预测未来100年热重盆地的状态。这个国际团队将由经验丰富的海洋和冰川科学家组成，他们将使用从成熟到尖端的一系列技术。该项目的结果将是彻底了解从接地线内陆几公里，穿过接地区，到冰架下的关键区域的TG系统。

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.