Multi-scale modelling of the ocean beneath ice shelves

对未来海平面的定量预测目前是不可能的，因为我们缺乏对气候变化如何影响地球大冰盖的质量平衡的了解。主要的不确定性是海洋环流和/或温度的变化将如何影响冰架的厚度和范围，以及从冰盖流出的流量将如何变化。对冰架下海洋的观测非常稀少，而且很难获得。因此，数值模拟被用来洞察冰架洞穴中的海洋流动的结构和动力学，以及它们对更大范围的影响。然而，与这一应用相关的复杂性意味着，基于流体静力学、均匀网格分辨率和垂直分层结构的模型可能会得到改进。这些复杂性包括存在一条接地线，在那里，在平均海平面以下的冰深下，水柱深度为零。这个非常有限的区域对于上面的冰架和相关的地面冰盖的重要性是巨大的，但这正是传统模型在代表真实世界时需要做出最大妥协的地方。此外，冰架底部的形状，以及冰层和开阔海洋之间前沿的陡峭变化，对海洋动力学造成了重要的限制，因此需要以类似于海底水深测量的方式在模型中很好地表示它们。这一点，加上可能是小规模的关键浮力驱动过程的表示，表明在水平和垂直方向上都使用了不均匀的分辨率。在这个项目中，我们将采用我们最先进的数值模式来研究漂浮冰架下洞穴中的海洋环流。三维中的非结构化和各向异性动态自适应网格方法将允许以比以前更大的分辨率和几何灵活性进行模拟。模型开发将根据早期的模型结果进行基准测试，并在一系列测试问题上进行验证。菲尔奇纳-罗恩冰架和松岛冰架下的真实世界应用程序将用于根据观测数据(包括新的Autosub数据)校准和验证该模型。将在这些领域开展非常及时的新科学，该项目也将是将冰架洞穴纳入未来全球海洋模型的重要一步。最终结果将是更好地理解冰架下发生的物理过程，并将成为一个强大的工具，使冰架能够明确地纳入未来全球范围的海洋和气候模型。该项目与NERC战略非常契合。特别是，对冰盖未来对海平面上升的贡献的预测被视为一项高度优先的目标，涉及气候系统、地球系统科学和自然灾害等主题。开发下一代气候模型也是气候系统和技术主题的优先事项。

Quantitative prediction of future sea level is currently impossible because we lack an understanding of how the mass balance of the Earth's great ice sheets can be affected by climate change. Chief among the uncertainties are how changes in ocean circulation and/or temperature will influence the thickness and extent of the ice shelves and how the outflow from the ice sheet will change in response. Observations of the ocean under ice shelves are very sparse and difficult to obtain. Hence, numerical modelling has been used to provide insight into the structure and dynamics of the ocean flow in ice shelf cavities, as well as their influence on the larger scale. However, the complexities associated with this application means that models based upon hydrostatic dynamics, uniform mesh resolution and a layered structure in the vertical, may be improved upon. These complexities include the presence of a grounding line where the water column depth goes to zero under ice deep below mean sea level. The importance of this very limited region to the ice shelf above, and the associated grounded ice sheet, is massive but this is exactly the point where conventional models need to make the largest compromises in representing the real world. Also, the shape of the base of the ice shelf, and the steep change at the front between the ice and the open ocean, place important constraints on the ocean dynamics and hence they need to be represented well in a model in a similar manner to sea floor bathymetry. This, along with the representation of critical buoyancy driven processes that may be of small scale, points towards the use of non-uniform resolution in both the horizontal and vertical directions. In this project we will adapt our state-of-the-art numerical model to study the ocean circulation in the cavities beneath floating ice shelves. Unstructured and anisotropic dynamically-adaptive mesh methods in three dimensions will allow simulations with a resolution and geometric flexibility that is greater than has been possible before. Model developments will be benchmarked against earlier model results and validated on a hierarchy of test problems. Real world applications under the Filchner-Ronne and Pine Island Glacier ice shelves will be used to calibrate and validate the model against observational (including new Autosub) data. Highly timely new science will be preformed in these areas, and this project will also be an important step towards the inclusion of ice shelf cavities in global scale ocean models of the future. The final result will be an improved understanding of the physical processes occurring under ice shelves, and a powerful tool that will enable the explicit inclusion of ice shelves in global scale ocean and climate models of the future. This project fits well with NERC strategy. In particular the prediction of the future contribution of the ice sheets to sea level rise is seen as a high priority goal that cuts across the themes of Climate Systems, Earth System Science and Natural Hazards. Development of the next generation climate models is also a priority for the Climate Systems and Technologies themes.