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.

冰架上的表格冰山的产犊占每年从南极洲失去的所有冰的一半。当全厚性裂缝（称为裂谷）通过冰架水平传播时，冰山会形成。由此产生的冰山的大小可能是数千平方公里，可能会影响野生动植物，运输和海洋循环，并可以改变保留的冰架的形状和稳定性，随后对冰出和海平面上升产生影响。产犊的时机目前是不可预测的，仅在某些冰盖模型中仅以表面包含，例如，一旦达到一定的厚度，就可以去除冰。已经观察到裂痕每天最多几公里，或者非常缓慢地迅速传播，停滞了数年甚至几十年。虽然已经很好地确定冰架塌陷会导致冰川加速，但最近的观察结果也直接显示出中度的产犊事件，并立即影响冰流和基础熔体速率，这表明迫切需要限制此过程的时机以及它是否会加速未来。同时，只要在小规模和大尺度上的行为通过观察值校准，由工程应用驱动的裂缝近似方法的发展使数值表示离散的裂缝成为可能。目前，缺乏观察结果限制了这种建模在冰川学中的价值。我们的研究结合了对南极洲首发冰架上裂谷生长的直接观察，以及对同一冰样品的实验实验，当将其连接在一起时，它们在多个尺度上产生了骨折过程的前所未有的细节。使用新的可扩展相位场模型将这种细节级别应用于断裂问题，该模型允许使用裂纹边界处的漫差接口将显微镜过程映射到低分辨率的冰盖尺度网格上。我们将进行实验室观察，以了解裂纹如何在晶体水平上与冰相互作用，并原位观察裂纹在公里水平上与冰架相互作用，以验证和测试该模型。这将阐明裂谷生长和控制其速率的物理冰的背后的三维机制。冰盖模型中如何在冰盖模型中表示产犊过程的逐步改变，从地球科学界有好处，从需要估算冰架支撑压力的冰盖模板以及产犊对接地线动态的影响到大规模的地球 - 依靠准确的冰架几何形状来限制淡水通量和海冰形成速率的系统模块。