Collaborative Research: Evaluating Retreat in the Amundsen Sea Embayment: Assessing Controlling Processes, Uncertainties, and Projections

在人类感兴趣的时间尺度上对冰川运动进行准确的重建和预测，需要更好地理解现有的观测结果，并有能力对控制冰流的关键过程进行建模。事实上，许多这些过程是相互关联的，受到数据的松散约束，不仅涉及冰，还涉及大气、海洋和固体地球，这使得这是一项具有挑战性的努力，但这对于地球系统建模以及由此产生的气候和海平面预测至关重要，这些预测可以提供给全世界的决策者。根据南极西部冰盖现有的冰量及其流入和/或融化到海洋的能力，它的完全崩溃将导致全球海平面上升3.3至5米，使其稳定性和变化率的科学问题具有全球社会意义。无论最终是否会发生崩塌，在考虑沿海人口中心的命运时，有必要更好地了解南极西部在未来几十年和几个世纪对海平面的潜在贡献。最近对西南极洲阿蒙森海海湾的观察表明，它正在经历比该大陆任何其他地区更快的物质损失。目前，这个海湾的长期稳定性是未知的，理论和观察都表明，崩溃是可能的。本研究的重点是这一关键区域。我们将根据现有观测对冰盖模型进行测试，改进模型中关键过程的处理，并通过不确定性评估进行预测。这是一项为期三年的建模研究，利用开源的冰盖系统模型与其他模型协作，改进对未来海平面变化的预测。项目目标是：1。2.对Amundsen Sea Embayment部门过去二三十年的发展进行后推，以确定控制过程，合并和测试参数化，评估和改进模型初始化、启动和性能；2 .利用面向区域过程模型的敏感性研究对模型进行改进，为关键子网格尺度过程创建数值上有效的参数化；3 .预测阿蒙森海海湾在今后几个世纪的一系列可能演变及其各自对海平面的贡献；确定后估误差的来源，并对预估中的不确定性进行评估，包括在各种强迫和模式中包含或遗漏物理过程的情况下可能产生的一系列结果。目前，阿蒙森海海湾的长期稳定性是未知的，理论（“海洋冰盖不稳定假说”）和观测（快速变薄和接地线后退接近河床加深的内陆地区）都表明崩塌是可能的。但不完全了解的物理过程（例如，基础水文、流变学和滑动；潮汐效应；沿大陆架和接地带内的冰海相互作用）和缺乏分辨率的基础地形数据集使得最终结果不确定。因此，迫切需要对该地区进行高分辨率模拟，其中包括在高阶冰盖模型中控制物理过程的数值表示（其中许多适用于其他地方），该模型能够吸收最近的观测结果，并提供与模型和数据限制相关的不确定性分析。通过关注阿蒙森海湾作为连接地区在10 - 10000米尺度使用层次结构的一个,两个,三维模型和灵敏度分析工具构建到冰盖系统模型,该项目旨在产生(1)迄今为止最可靠的结果相比,研究只考虑了一个冰流或整个冰原和(2)的估计错误带来的不同的动态响应数据,模型参数化,和营力。考虑到这些不确定性，该项目将产生一系列具有特征趋势的预测，这些预测可以在未来的观测数据集中识别出来。随着新数据的出现，可以从本研究生成的预测路径中剔除一些预测的变化率。

Accurate reconstructions and predictions of glacier movement on timescales of human interest require a better understanding of available observations and the ability to model the key processes that govern ice flow. The fact that many of these processes are interconnected, are loosely constrained by data, and involve not only the ice, but also the atmosphere, ocean, and solid Earth, makes this a challenging endeavor, but one that is essential for Earth-system modeling and the resulting climate and sea-level forecasts that are provided to policymakers worldwide. Based on the amount of ice present in the West Antarctic Ice Sheet and its ability to flow and/or melt into the ocean, its complete collapse would result in a global sea-level rise of 3.3 to 5 meters, making its stability and rate of change scientific questions of global societal significance. Whether or not a collapse eventually occurs, a better understanding of the potential West Antarctic contribution to sea level over the coming decades and centuries is necessary when considering the fate of coastal population centers. Recent observations of the Amundsen Sea Embayment of West Antarctica indicate that it is experiencing faster mass loss than any other region of the continent. At present, the long-term stability of this embayment is unknown, with both theory and observations suggesting that collapse is possible. This study is focused on this critical region. We will test an ice-sheet model against existing observations, improve treatment of key processes in the model, and make projections with uncertainty assessments.This is a three-year modeling study using the open-source Ice Sheet System Model in coordination with other models to improve projections of future sea-level change. Project goals are to:1. hindcast the past two-to-three decades of evolution of the Amundsen Sea Embayment sector to determine controlling processes, incorporate and test parameterizations, and assess and improve model initialization, spinup, and performance;2. improve the model by utilizing sensitivity studies with regional process-oriented models to create numerically efficient parameterizations for key sub-grid-scale processes;3. project a range of likely evolutions of the Amundsen Sea Embayment sector and their respective contributions to sea level in the next several centuries;4. attribute sources of errors in the hindcast and provide an assessment of the uncertainties in the projections, including a range of likely outcomes given various forcings and inclusion or omission of physical processes in the model.At present, the long-term stability of the Amundsen Sea Embayment is unknown, with both theory (the "marine ice sheet instability hypothesis") and observations (rapid thinning and grounding-line retreat approaching regions where the bed deepens inland) suggesting that collapse is possible. But incompletely understood physical processes (e.g., basal hydrology, rheology, and sliding; tidal effects; ice-ocean interaction along the shelf and within the grounding zone) and lack of resolution in basal topography datasets making the ultimate outcome uncertain. Thus, there is a pressing need for high-resolution simulations of this region that include numerical representations of controlling physical processes (many of which are applicable elsewhere) within a higher-order ice-sheet model capable of assimilating recent observations and providing uncertainty analyses associated with model and data limitations. By focusing on the Amundsen Sea Embayment as a connected region across the 10-10,000-meter scales using a hierarchy of one, two, and three-dimensional models along with the sensitivity analysis tools built into the Ice Sheet System Model, this project aims to produce (1) the most reliable results to date when compared with studies that consider only one ice stream or the entire ice sheet and (2) estimates of differing dynamic responses arising from errors in data, model parameterizations, and forcings. Given the uncertainties, the project will produce a range of predictions with characteristic trends that can be recognized within future observational data sets. As new data become available, some predicted rates of change could be culled from the predictive paths generated by this study.