INSIGT: Investigating Shear-margin Interactions with Grounding-line Transitions

由于出口冰川和冰流的快速和局部冰流，南极洲正在失去大部分质量。虽然出口冰川的位置和宽度通常在很大程度上受到下垫景观的控制（例如，冰流通过山脉的间隙），但冰流大多在沉积盆地上流动，其侧向边界很少或没有地形控制。尽管存在这些差异，冰流和出口冰川都可能倾向于不稳定的退缩。造成这种快速冰损失的关键机制之一是海洋冰盖的不稳定，在这种不稳定中，在测深线向内陆倾斜的地区可能会引起持续的退缩。这种不稳定性主要研究了具有冰流横向地形边界的出口冰川。因此，本项目探讨了海洋冰盖不稳定性对边缘没有地形边界的冰流的影响和适用性。该项目的目标是了解海洋冰盖不稳定的机制是否以及如何适用于冰流。为了实现这一目标，研究小组将研究冰流对接地线后退的反应，在接地线上，冰与床失去联系，开始漂浮在海洋中。该小组将重点了解接地线后退和冰流横向边界之间的耦合，而不是接地线后退的开始。假设冰流的宽度和流速都会受到退缩的影响，因为冰流动力学对床层、边缘和驱动应力之间的力平衡非常敏感。更具体地说，研究小组假设河床坡度与冰流的关系不如与出口冰川的关系，因为冰流有可能因退缩而变宽，即使在没有向陆地倾斜的河床的情况下，也会加剧冰的损失。然而，这一机制取决于对加宽和水流加速的阻力，这敏感地依赖于冰和下面沉积层之间的冰下水文。该团队将通过为此目的开发的定制数值模拟方法来验证其假设，并将模型预测与西南极洲简单海岸地区过去冰流的观测约束进行比较。该奖项反映了美国国家科学基金会的法定使命，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，被认为值得支持。

Antarctica is losing most of its mass through rapid and localized ice flow in outlet glaciers and ice streams. While the position and width of outlet glaciers are often largely controlled by the underlying landscape (e.g., ice flow through gaps in mountains), ice streams flow mostly over sedimentary basins with little or no topographic control on their lateral boundaries. Despite these differences, both ice streams and outlet glaciers are potentially prone to unstable retreat. One of the key mechanisms responsible for this rapid ice loss is the marine ice-sheet instability, in which continued retreat may be induced in areas where the bathymetry slopes inland. This instability has been primarily studied for outlet glaciers with lateral topographic bounds on ice flow. Consequently, this project explores the effect and applicability of the marine ice-sheet instability to ice streams without those topographic bounds on their margins.The goal of this project is to understand whether and how the mechanism of the marine ice-sheet instability applies to ice streams. To achieve this goal, the team will study how ice streams respond to the retreat of the grounding line, where ice loses contact with the bed and starts floating in the ocean. The team will focus on understanding the coupling between grounding-line retreat and ice-stream lateral boundaries rather than initiation of grounding-line retreat. It is hypothesized that both the width and flow speed of ice streams would be affected by retreat, because ice-stream dynamics are extremely sensitive to the force-balance between the bed, margins, and driving stress. More specifically, the team hypothesizes that the bed slope is less relevant in the case of ice streams than it is for outlet glaciers, because ice streams have the potential to widen in response to retreat, exacerbating ice loss even in the absence of a landward sloping bed. This mechanism, however, depends on the resistance to both widening and flow acceleration, which is sensitively dependent on the subglacial hydrology between ice and the sedimentary layer underneath. The team will test its hypothesis through a customized numerical modeling approach developed for this purpose and will compare model predictions to observational constraints from past ice flow in the Siple Coast region of West Antarctica.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.