Simulating UNder ice Shelf Extreme Topography (SUNSET)

模拟冰架下极端地形（日落）

• 批准号: NE/X013782/1
• 负责人: John Taylor
• 金额: $ 43.5万
• 依托单位: University of Cambridge
• 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%2FX013782%2F1
• 关键词: Simulating; UNder; ice; Shelf; Extreme

Global average sea level is rising at an ever-accelerating rate. Given the huge economic and societal impacts of this change, accurate forecasts of sea level are urgently needed to inform policymakers considering mitigation and adaptation strategies. Melting of the Antarctic and Greenland ice sheets currently contributes about one third of sea-level rise. The future of this melting is highly uncertain, and the worst-case scenario involves a substantial ice-sheet contribution to dangerous sea-level rise. The largest ice-sheet contribution to sea level occurs when the ocean melts the base of ice shelves (floating extensions of the grounded ice sheet), increasing the flow of grounded ice into the ocean. The melt rate of ice shelves is determined by the transfer of heat from the ocean towards the ice. Recently, extreme topographic features, including step-like terraces and 1-10 km wide channels, have been discovered to be ubiquitous on the underside of rapidly melting ice shelves. These features significantly modify the patterns and rates of melting, and so are crucial to predicting sea level. However, such features are generally too small to be resolved in climate models and their effect must be understood and explicitly built into these models. We will investigate how extreme topography on the underside of ice shelves changes ocean currents and melting. Beneath ice shelves with a smooth, gradually sloping base, melting can be viewed as a vertical process, and this is how it is currently represented in climate models. However, observations show that melting on the steeply sloping sides of extreme ice topography is actually horizontal, and much faster than the melting of a smooth ice base. In addition, turbulent ocean eddies generated by extreme topographic features will mix warm water up towards the ice, further enhancing the melting. We will observe the influence of extreme ice topography beneath an Antarctic ice shelf using pressurised hot water to drill through more than a kilometre of ice, enabling access to the ocean cavity beneath. We will study the controls on melting using a targeted suite of the latest observational measurements: radar and sonar to track the ice topography and melting, and acoustic ocean current profiling and a string of temperature sensors to monitor the mixing of ocean heat towards the ice. This will provide a unique dataset of the close interaction between ocean mixing and ice melting.We will then combine these observations with a hierarchy of computer simulations to develop a new representation of the effect of extreme ice topography in climate models. We will first simulate the flow around extreme topographic features using high-resolution large-eddy simulations, which resolve the ocean turbulence. This will provide insight into the mixing of warm water to the ice base, and its interaction with melting. We will then use an ocean model to study the role of ice channel geometry on the melt rate and flow properties. Using these simulations, we will develop mathematical formulae to represent the influence of extreme ice topography. We will implement these formulae into the ocean model and test its ability to represent the influence of extreme ice topography in climate models.

全球平均海平面正在以不断加速的速度上升。鉴于这种变化的巨大经济和社会影响，迫切需要对海平面的准确预测，以告知考虑缓解和适应策略的决策者。目前，南极和格陵兰冰盖的融化占海平面上升的三分之一。这种融化的未来是高度不确定的，最坏的情况涉及对危险海平面上升的巨大冰期贡献。当海洋融化冰架的底部（地面冰盖的浮动延伸）时，最大的冰片贡献是对海平面的最大贡献，从而增加了接地冰的流入海洋。冰架的熔体速率取决于将热量从海洋转移到冰上的。最近，在快速融化的冰架的底面上，已经发现极端的地形特征，包括阶梯状的露台和1-10公里宽的通道。这些特征显着改变了熔化的模式和速率，因此对于预测海平面至关重要。但是，这种功能通常太小，无法在气候模型中解决，必须理解并明确内置这些特征。我们将研究冰架上底面的极端地形如何改变洋流和融化。在带有光滑，逐渐倾斜的底座的冰架下，熔化可以看作是垂直过程，这就是气候模型中目前表示的方式。但是，观察结果表明，在极端冰形地形的陡峭倾斜的侧面融化实际上是水平的，并且比光滑的冰基的融化要快得多。此外，极端地形特征产生的湍流海洋涡流将使水向冰融化，从而进一步增强熔化。我们将使用加压热水在南极冰架下观察到极端冰架的影响，以钻多公里以上的冰，从而可以进入下方的海洋腔。我们将使用最新观测测量的目标套件来研究熔化的控件：雷达和声纳，以跟踪冰形和融化，以及声海洋电流谱分析和一系列温度传感器，以监视海洋热量朝冰的混合。这将为海洋混合与冰融化之间的紧密相互作用提供独特的数据集。然后，我们将将这些观察结果与计算机模拟的层次结合在一起，以开发出在气候模型中极端冰形效果的新表示。我们将使用高分辨率大型模拟来模拟极端地形特征周围的流量，从而解决海洋湍流。这将提供有关将温水与冰基混合在一起的洞察力，以及与熔化的相互作用。然后，我们将使用海洋模型来研究冰通道几何形状对熔体速率和流量特性的作用。使用这些模拟，我们将开发数学公式来代表极端冰形的影响。我们将将这些公式实施到海洋模型中，并测试其在气候模型中代表极端冰形影响的能力。