A novel approach to constraining ice sheet models with glacial geomorphology

格陵兰岛和南极洲的冰盖拥有足够的水，可以使全球海平面上升约65米，并且目前正在加速失去质量。对未来质量损失的预测很难做出，这意味着冰盖的贡献是未来海平面上升估计的一个很大的不确定性来源。做出这些预测的数值模型需要观测冰盖的行为来验证和改进，但是现存冰盖的记录很短。通过研究末次冰期（约120，000年至约10，000年前）冰盖所占据的区域，可以获得冰盖行为的更长记录。这一时期存在的冰盖以冰川地貌的形式留下了大量的动态行为证据。在天气预报等领域，模型的改进是通过后测来实现的，后测是模拟过去的条件并将其与历史数据进行比较的行为。然而，古冰盖的模拟很少充分利用冰川地貌记录。这个项目是一个有意识的尝试，汇集冰盖建模和冰川地貌学的不同学科，以改善后报程序。有了这个动机，我的目标是开发和应用工具，验证冰盖模型与冰川地貌。在最后一次冰期，格陵兰岛和南极冰盖更大，大部分北美，西北欧和巴塔哥尼亚冰川。关于这些主要冰盖的行为的信息目前被储存起来。我将整理有关覆盖这五个地区的冰盖的信息，并将其纳入一个标准化的数据库。从这一点上，我将产生第一个全球规模的经验重建冰盖的范围和行为在末次冰期。我还将使用最先进的冰盖模型来模拟这些冰盖的行为。这些冰盖将被模拟数百次，每次模拟都有一组单独的输入值，以捕捉到我们目前对冰盖流动和过去气候条件的了解有限的情况下可能出现的各种冰结构。我将开发一套新的工具，这将量化模型预测的古-从冰川地貌学数据集推断的冰盖。为了过滤掉极端不真实的模型模拟，我将首先将模型输出与我重建的冰盖范围进行比较。然后，根据再现时间、流动方向、流动模式变化、边缘位置，然后，我将联合收割机结合最符合地貌数据的模拟结果，对末次冰期存在的主要冰盖的行为进行高分辨率模拟周期模拟的冰盖将作为现有冰盖的重要模拟物，展示对冰盖行为的控制，如地形，海平面和气候，如何使这些冰盖退缩，以及它们不断变化的几何形状如何促成过去海平面的快速上升，如融水脉冲和主要的冰山排放事件。我的模型数据比较程序还将确定模型难以复制古冰盖行为的区域。这将突出模型中的缺陷，为模型开发提供目标。此外，未来南极和格陵兰冰盖的模型依赖于准确模拟其过去的范围和行为。我进行的程序和模型实验将改善冰盖模型如何坚持这一历史。因此，我的项目将带来冰盖模型测试和校准方式的逐步变化，并为其他研究人员提供一个新的框架。

The ice sheets in Greenland and Antarctica hold enough water to raise global sea level by ~65 m, and are currently losing mass at an accelerating rate. Predictions of future mass loss are difficult to make, meaning that the contribution of ice sheets is a large source of uncertainty for estimates of future sea level rise. The numerical models which make these predictions need observations of ice sheet behaviour for validation and improvement, but the record of extant ice sheets is short. A longer record of ice sheet behaviour can be obtained by studying the regions occupied by ice sheets during the last glacial period (~120,000 to ~10,000 years ago). The ice sheets which existed during this time left behind abundant evidence for their dynamic behaviour in the form of glacial landforms. In fields such as weather forecasting, model improvement has been achieved by hindcasting - the act of simulating past conditions and comparing them to historical data. However, simulations of palaeo-ice sheets rarely utilise the glacial landform record to its full extent. This project is a deliberate attempt to bring together the rather disparate disciplines of ice sheet modelling and glacial geomorphology to improve hindcasting procedures. With this motivation, my aim is to develop and apply tools for validating ice sheet models with glacial geomorphology.During the last glacial, the Greenland and Antarctic ice sheets were larger and much of North America, Northwest Europe and Patagonia was glaciated. Information regarding the behaviour of these major ice sheets is currently disparately stored. I will collate information regarding the ice sheets that covered these five regions into a single standardised database. From this, I will produce the first global scale empirical reconstruction of ice sheet extent and behaviour during the last glacial. I will also use a state of the art ice sheet model to simulate the behaviour of these ice sheets. The ice sheets will be simulated hundreds of times, each simulation with a separate set of input values, to capture the full range of likely ice configurations given the current limitations of our knowledge regarding how ice sheets flow and past climate conditions.To evaluate my model simulations, I will develop a new set of tools which will quantify how well the model predicts the properties of palaeo-ice sheets inferred from the dataset of glacial geomorphology. To filter out extremely unrealistic model simulations, I will first compare model output to my reconstructed ice sheet extent. An overall score of model performance will then be calculated from the ability to reproduce the timing, flow direction, changes in flow pattern, margin position, erosive capabilities and basal pressure gradients that are recorded by glacial geomorphology.I will then combine the simulations which best conform to the geomorphological data to produce a high resolution simulation of the behaviour of the major ice sheets which existed during the last glacial cycle. The simulated ice sheets will serve as important analogues for existing ice sheets, demonstrating how controls on ice sheet behaviour such as topography, sea level and climate conditioned these ice sheets to retreat, and how their changing geometries contributed to past rapid sea level rise, such as meltwater pulses and major iceberg discharge events. My model-data comparison procedure will also identify regions where the model struggles to replicate the palaeo-ice sheet behaviour. This will highlight deficiencies in the model, providing targets for model development. Furthermore, models of the future Antarctic and Greenland ice sheets rely upon accurately simulating their past extent and behaviour. The procedures and model experiments I conduct will improve how ice sheet models adhere to this history. Therefore, my project will bring about a step-change in how ice sheet models are tested and calibrated and offer a new framework for other researchers to utilise.