CAREER: Taking Process-based Models to the Field to Understand the Possibility and Implication of an Internal Shear Band Forming in Ice Flowing over Rough Topography

职业：将基于过程的模型带到现场，了解在粗糙地形上流动的冰中形成内部剪切带的可能性和影响

• 批准号: 2142651
• 负责人: Jenny Suckale
• 金额: $ 68.5万
• 依托单位: Stanford University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2022
• 资助国家: 美国
• 起止时间: 2022-04-01 至 2027-03-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2142651&HistoricalAwards=false
• 关键词: CAREER; Taking; Process; based; Models

Ice sheets in Antarctica and Greenland lose the vast majority of their ice mass through narrow drainage routes that are embedded into comparatively stagnant ice. The sharp difference in ice speed inside and outside of these drainage routes is comparable in magnitude to the speed difference between a race car and a pedestrian, begging the question how ice with relatively similar properties across the entirety of the ice sheet behaves so differently. The most convincing explanation to date is that rapidly moving ice has lost direct contact with the bedrock below and is slipping towards the ocean while slowly moving ice remains connected to the bed and is moving through internal deformation. Compelling as this explanation might be, it does not address where in the ice column the slip occurs that enables fast motion, but this location is essential for assessing how sliding, and the associated ice motion, responds to climate change. If slip occurs where ice and rock meet at the base of the ice sheet, water infiltration from a warming ocean could directly affect ice speed. If slip occurs close to the base of the ice sheet but within the ice itself, this feedback would likely be less immediate. The research plan is integrated with a collaborative educational program that aims to increase participation in polar science for high-school students from historically disadvantaged communities that are prone to be impacted by sea-level rise in the near future.The goal of this CAREER proposal is to understand the possibility and implications of an internal shear band forming in ice flowing over rough topography by developing a suite of customized numerical models that will be available as open-source tools to the glaciological community for usage and further development. The team hypothesizes that ice flowing over a hard bed with rough topography in the non-cavitating limit may experience sufficient strain localization in the ice just above topographic highs to form an internal shear band through creep instability despite advective cooling as the ice thins and accelerates. The deformation in this internal shear band is highly localized and reminiscent of sliding, highlighting that flow and sliding may be end members that are connected by a spectrum of increasingly localized englacial deformation. The team will test its hypothesis through a three-step process by (1) identifying the nondimensional conditions that are required for internal-shear band formation for a bed with an idealized topography, (2) generalizing insights to beds with more realistic, fractal bed topography and comparing results to existing field observations, and (3) producing continental-scale assessments of where an internal shear band could form for both Greenland and 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.

南极洲和格陵兰岛的冰盖通过嵌入相对停滞的冰中的狭窄排水通道失去了绝大多数的冰质。这些排水路线内外的冰速度的巨大差异与赛车和行人之间的速度差异相当，这就引出了一个问题，即在整个冰盖上具有相对相似属性的冰如何表现得如此不同。迄今为止，最令人信服的解释是，快速移动的冰已经失去了与下面基岩的直接接触，正在滑向海洋，而缓慢移动的冰仍然连接到床，并通过内部变形移动。尽管这一解释可能令人信服，但它并没有解决冰柱中发生滑动的位置，从而使快速运动成为可能，但这个位置对于评估滑动以及相关的冰运动如何响应气候变化至关重要。如果滑动发生在冰盖底部的冰和岩石相遇的地方，那么来自变暖海洋的水渗透可能直接影响冰的速度。如果滑动发生在冰盖底部附近，但在冰本身内部，这种反馈可能不会那么直接。该研究计划与一项合作教育计划相结合，该计划旨在增加来自历史上弱势社区的高中生对极地科学的参与，这些社区容易受到海洋的影响。本CAREER建议的目标是通过开发一套定制的数值模拟，了解在粗糙地形上流动的冰中形成内部剪切带的可能性和影响。这些模型将作为开放源代码工具提供给冰川学界使用和进一步开发。该团队假设，在非空化极限下，冰在具有粗糙地形的硬床上流动，可能会在地形高点上方的冰中经历足够的应变局部化，以通过蠕变不稳定性形成内部剪切带，尽管随着冰变薄和加速而对流冷却。在这个内部剪切带的变形是高度本地化的，让人联想到滑动，突出的流动和滑动可能是端部成员连接的光谱越来越本地化的内冰变形。该团队将通过三步过程来测试其假设，即（1）确定具有理想地形的床层内部剪切带形成所需的无量纲条件，（2）将见解推广到具有更现实的分形床层地形的床层，并将结果与现有的现场观测结果进行比较，（3）生产大陆-该奖项反映了NSF的法定使命，并被认为值得通过使用基金会的学术价值和更广泛的影响审查标准。