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

要准确重建和预测人类感兴趣的时间尺度上的冰川运动，需要更好地了解现有的观测结果，并有能力对支配冰流的关键过程进行建模。其中许多过程是相互关联的，受到数据的松散限制，不仅涉及冰，而且还涉及大气、海洋和固体地球，这使得这一努力具有挑战性，但对于地球系统建模以及由此产生的气候和海平面预测是必不可少的，这些预测将提供给世界各地的政策制定者。根据西南极冰盖中存在的冰量及其流入和/或融化海洋的能力，它的完全崩溃将导致全球海平面上升3.3至5米，使其稳定性和变化速度成为具有全球社会意义的科学问题。无论最终是否发生崩塌，在考虑沿海人口中心的命运时，有必要更好地了解未来几十年和几个世纪西南极对海平面的潜在贡献。最近对南极洲西部阿蒙森湾的观察表明，它正在经历比大陆其他任何地区更快的质量损失。目前，这个海湾的长期稳定性尚不清楚，理论和观测都表明有可能坍塌。本研究正是针对这一关键区域展开的。我们将根据现有的观测结果测试冰盖模型，改进对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，使用开放源码的冰盖系统模型与其他模型协调，以改进对未来海平面变化的预测。项目目标是：1.回顾阿蒙森海湾部门过去二三十年的演变，以确定控制过程，纳入和测试参数化，评估和改进模式的初始化、自旋和性能；2.利用区域面向过程的模式的敏感性研究，改进模式，为关键的次网格尺度过程建立有效的数值参数；3.预测阿蒙森海湾部门在未来几个世纪可能的一系列演变及其对海平面的各自贡献；4.后播中误差来源的属性，并对预测中的不确定性进行了评估，包括在模式中考虑到各种强迫和物理过程的一系列可能结果。目前，阿蒙森海湾的长期稳定性尚不清楚，理论(“海洋冰盖不稳定性假说”)和观测(快速变薄和基准线后退接近海床向内陆加深的区域)都表明坍塌是可能的。但不完全了解物理过程(例如，基础水文学、流变学和滑动；潮汐效应；沿陆架和接地带内的冰-海洋相互作用)，以及基础地形数据集缺乏分辨率，使得最终结果不确定。因此，迫切需要对这一区域进行高分辨率的模拟，其中包括控制物理过程的数字表示(其中许多过程适用于其他地方)，该模型能够吸收最近的观测并提供与模型和数据限制有关的不确定性分析。通过使用一维、二维和三维模型的层次结构以及冰盖系统模型中内置的敏感性分析工具，将阿蒙森海湾作为一个跨越10-10,000米尺度的连通区域进行重点研究，该项目旨在产生(1)与只考虑一股冰流或整个冰盖的研究相比，迄今最可靠的结果，以及(2)对数据、模型参数化和强迫中的错误引起的不同动态响应的估计。考虑到不确定性，该项目将产生一系列具有特征趋势的预测，这些趋势可以在未来的观测数据集中得到识别。随着新数据的出现，一些预测的变化率可能会从这项研究产生的预测路径中挑选出来。

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.