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，因为我们不了解地球大冰盖的物质平衡如何受到气候变化的影响。主要的不确定因素是，海洋环流和（或）温度的变化将如何影响冰架的厚度和范围，以及冰盖的流出量将如何相应变化。对冰架下海洋的观测非常稀少，而且很难获得。因此，数值模拟已被用于深入了解冰架空洞中海洋流动的结构和动力学，以及它们对更大尺度的影响。然而，与此应用程序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。这些复杂性包括在平均海平面以下的冰层下，水柱深度为零的接地线的存在。这个非常有限的区域对上面的冰架和相关的接地冰原的重要性是巨大的，但这正是传统模型在代表现实世界时需要做出最大妥协的地方。此外，冰架底部的形状，以及冰面和开阔海洋之间的陡峭变化，对海洋动力学产生了重要的限制，因此，它们需要在一个与海底测深类似的模型中得到很好的表现。这一点，连同可能是小规模的关键浮力驱动过程的表示，指向在水平和垂直方向上使用非均匀分辨率。在这个项目中，我们将采用我们最先进的数值模型来研究漂浮冰架下空洞中的海洋环流。三维非结构化和各向异性动态自适应网格方法将使模拟具有比以前更大的分辨率和几何灵活性。模型开发将根据早期的模型结果进行基准测试，并在测试问题的层次结构上进行验证。Filchner-Ronne和Pine Island冰川冰架下的实际应用将用于根据观测数据（包括新的Autosub）校准和验证模型。在这些领域将会出现非常及时的新科学，这个项目也将是在未来的全球尺度海洋模型中包含冰架空洞的重要一步。最终的结果将提高对冰架下发生的物理过程的理解，并提供一个强有力的工具，使冰架能够明确地包括在未来全球尺度的海洋和气候模式中。这个项目非常符合NERC的战略。特别是预测冰盖对海平面上升的未来贡献被视为跨越气候系统、地球系统科学和自然灾害主题的高度优先目标。开发下一代气候模式也是气候系统和技术主题的一个优先事项。

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.