RIFT-TIP: Rates of Ice Fracture and Timing of Tabular Iceberg Production

RIFT-TIP：冰破裂率和板状冰山产生时间

• 批准号: NE/X014991/1
• 负责人: Oliver Marsh
• 金额: $ 132.5万
• 依托单位: British Antarctic Survey
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2023
• 资助国家: 英国
• 起止时间: 2023 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FX014991%2F1
• 关键词: RIFT; TIP; Rates; Ice; Fracture

Calving of tabular icebergs from ice shelves accounts for around half of all the ice lost from Antarctica each year. The icebergs form when full-thickness fractures (known as rifts) propagate horizontally through the ice shelf. The resulting icebergs can be thousands of square kilometres in size, can impact wildlife, shipping and ocean circulation and can modify the shape and stability of the ice shelves which remain, with a subsequent impact on ice discharge and sea level rise. The timing of calving is currently unpredictable and is only included superficially in some ice sheet models, for example by removing ice once a certain thickness is reached. Rifts have been observed to propagate very rapidly, at up to several kilometres per day, or very slowly, stagnating for years or even decades. Whilst it is well established that ice shelf collapse can lead to glacier acceleration, recent observations also show moderate calving events directly and immediately impacting ice flow and basal melt rate, indicating an urgent need to constrain the timing of this process and whether it will accelerate in the future. Simultaneously, developments in fracture approximation methods driven by engineering applications have made it possible to represent discrete fractures numerically, provided the behaviour at the small-scale and large-scale is calibrated with observations. Lack of observations currently limits the value of this type of modelling in glaciology. Our research combines direct observations of rift growth on the Brunt Ice Shelf in Antarctica with laboratory experiments on samples of the same ice, which when linked together produce unprecedented detail on the fracture process across multiple scales. This level of detail will be applied to the fracture problem using a new scalable phase-field model that allows microscale processes to be mapped onto a low-resolution ice-sheet-scale grid using diffuse interfaces at crack boundaries. We will conduct laboratory observations of how cracks interact with ice at the crystal level, and in situ observations of how rifts interact with the ice shelf at the kilometre level to validate and test this model. This will illuminate the three-dimensional mechanism behind rift growth and the physical ice properties that control its rate. A step-change improvement in how the calving process is represented in ice sheet models has benefits across the geoscience community, from ice sheet modellers who need to estimate ice shelf buttressing stress and the impact of calving on grounding line dynamics, to large scale earth-system modellers which rely on accurate ice shelf geometry to constrain freshwater fluxes and rates of sea ice formation.

冰架上的扁平冰山崩解约占南极洲每年冰损失的一半。当全层裂缝（称为裂缝）水平地穿过冰架时，冰山就形成了。由此产生的冰山面积可达数千平方公里，可能影响野生动物、航运和海洋环流，并可能改变残留冰架的形状和稳定性，从而影响冰的排放和海平面上升。目前，冰解的时间是不可预测的，并且仅在一些冰盖模型中包含了表面上的内容，例如一旦达到一定厚度就将冰移除。据观察，裂缝的传播速度非常快，每天可达数公里，或者非常缓慢，停滞数年甚至数十年。虽然已经确定冰架崩塌会导致冰川加速，但最近的观测也显示，中度的产犊事件直接并立即影响冰流和基底融化速率，这表明迫切需要限制这一过程的时间以及它是否会在未来加速。与此同时，在工程应用驱动的裂缝近似方法的发展，使得它有可能代表离散裂缝数值，提供的行为在小规模和大规模的校准与观察。目前缺乏观测限制了这种类型的冰川学建模的价值。我们的研究结合了对南极洲布伦特冰架裂缝生长的直接观察和对同一冰样本的实验室实验，这些实验结合在一起时，在多个尺度上产生了前所未有的断裂过程细节。这一层次的细节将被应用到断裂问题，使用一个新的可扩展的相场模型，允许微尺度的过程被映射到一个低分辨率的冰盖规模的网格使用扩散界面在裂纹边界。我们将进行实验室观察裂缝如何与冰在晶体水平上相互作用，并在现场观察裂缝如何与冰架在千米水平上相互作用，以验证和测试这个模型。这将阐明裂缝增长背后的三维机制和控制其速度的冰的物理特性。在冰盖模型中如何表示产犊过程的阶跃变化改进在整个地球科学界都有好处，从需要估计冰架支撑应力和产犊对接地线动态影响的冰盖建模者，到依赖精确的冰架几何形状来约束淡水通量和海冰形成速率的大规模地球系统建模者。