EAR - Climate; Investigating Effects of 3-Dimensional and Non-Newtonian Mantle Viscosity on Relative Sea-Level Changes and Deglaciation History Since the Last Glacial Maximum

EAR——气候；

• 批准号: 2222115
• 负责人: Shijie Zhong
• 金额: $ 36.61万
• 依托单位: University of Colorado at Boulder
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2022
• 资助国家: 美国
• 起止时间: 2022-09-01 至 2025-08-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2222115&HistoricalAwards=false
• 关键词: EAR; Climate; Investigating; Effects; Dimensional

Some 26,000 years ago, much of North America and Europe was covered by ice sheets several kilometers thick. These ice sheets started to melt and by about 8,000 years ago they were mostly gone, but their meltwater caused the sea level to rise globally by about 130 meters. As the ice sheets melted, the land that used to support them gradually rose in response, while the vast ocean floors subsided under the load of added weight from the meltwater. This slow rising and falling of the Earth’s surface in response to deglaciation is called glacial isostatic adjustment (GIA). GIA tells us about sea-level change and ice sheet melting history, as well as flow in the Earth's mantle and even rotation of the Earth, but it is a huge topic requiring the effort of many scientists and highly sophisticated computational models. To make this effort more efficient, Dr. Zhong will be updating his software (CitcomSVE) and sharing it freely with other researchers. Dr. Zhong's own research group will address uncertainties in deglaciation history for the last 26,000 years, and seek to resolve conflicting modeling results from previous studies. If he is successful, his software can be used with confidence to project sea level change in the near future. This will help scientists, engineers and other stakeholders understand risks associated with sea level rise and take steps to improve resilience in the highest-risk coastal regions. GIA studies determine mantle viscosity and construct deglaciation history for the last ~26,000 years since the last glacial maximum (LGM). However, the two widely used ICE6G [Peltier et al., 2015] and ANU [Lambeck et al., 2017] ice models differ significantly, and so do their accompanying mantle viscosity models. Furthermore, while various studies of rock deformation including laboratory experiments and geodynamic modeling indicate that mantle viscosity is temperature- and stress-dependent (i.e., non-Newtonian) [e.g., Karato, 2008], observational evidence for the influence of non-Newtonian viscosity in GIA process remains elusive. This project has three objectives: 1) to construct an improved ice model and mantle viscosity model that explains the combined relative sea level (RSL) datasets used by the Peltier and Lambeck groups, 2) to seek observational evidence in GIA process for non-Newtonian mantle in quasi-L shaped RSL curves from locations near former ice sheet edges, and 3) to develop a publicly available finite element package CitcomSVE for modeling GIA and tidal deformation problems. This project consists of the following three tasks to accomplish these objectives. Task 1 is to further develop the newly upgraded, open-source package, CitcomSVE code, by including more efficient computational methods for solving Earth’s gravitational field and physically more realistic features such as mantle compressibility. Task 2 is to further analyze the RSL data considered by Peltier and Lambeck groups, to seek ice models and 1-D mantle viscosity models that better explain these RSL data at near-field and far-field sites and GRACE data, and to test the effects of 3-D mantle viscosity derived from seismic models and plate boundary viscosity on GIA observables. Task 3 is to examine the effects of non-Newtonian viscosity on simulations of the GIA process, to characterize the quasi-L shaped RSL curves at near-field sites, to understand causes of the quasi-L-shaped RSL curves in terms of deglaciation history and non-Newtonian viscosity, and to test the hypothesis that the effect of non-Newtonian viscosity is evident in the RSL observations.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

大约 26,000 年前，北美和欧洲的大部分地区被几公里厚的冰盖覆盖，这些冰盖开始融化，到大约 8,000 年前它们大部分消失了，但它们的融水导致全球海平面上升了约 130°。随着冰盖融化，支撑冰盖的陆地逐渐上升，而巨大的海底则在地球表面缓慢上升和下降的重量作用下下沉。冰川消退的过程称为冰川均衡调整（GIA），GIA 告诉我们有关海平面变化和冰盖融化历史，以及地幔流动甚至地球自转的信息，但这是一个需要付出努力的巨大课题。为了使这项工作更加高效，钟博士将更新他的软件（CitcomSVE）并与其他研究人员免费共享，钟博士自己的研究小组将解决这一问题。过去 26,000 年的冰消历史，并寻求解决先前研究中相互矛盾的建模结果。如果他成功了，他的软件就可以放心地用于预测不久的将来的海平面变化，这将有助于科学家、工程师和其他利益相关者。了解与海平面上升相关的风险，并采取措施提高风险最高的沿海地区的恢复能力 GIA 研究确定地幔粘度并构建自上次盛冰期以来过去约 26,000 年的冰消历史。 (LGM)。然而，两种广泛使用的 ICE6G [Peltier et al., 2015] 和 ANU [Lambeck et al., 2017] 冰模型存在显着差异，而且它们伴随的地幔粘度模型也存在显着差异。包括实验室实验和地球动力学模型在内的变形表明，地幔粘度与温度和应力有关（即非牛顿）[例如，Karato， [2008]，关于 GIA 过程中非牛顿粘度影响的观测证据仍然难以捉摸，该项目有三个目标：1）构建改进的冰模型和地幔粘度模型，以解释所使用的组合相对海平面（RSL）数据集。由 Peltier 和 Lambeck 小组进行，2) 在 GIA 过程中寻找来自前冰盖边缘附近位置的准 L 形 RSL 曲线中的非牛顿地幔的观测证据，以及3) 开发一个公开可用的有限元软件包 CitcomSVE，用于对 GIA 和潮汐变形问题进行建模 该项目包括以下三个任务来完成这些目标 任务 1 是进一步开发新升级的开源软件包 CitcomSVE 代码。通过包含更有效的计算方法来求解地球引力场和更现实的物理特征（例如地幔压缩性），任务 2 是进一步分析 Peltier 和 Lambeck 小组考虑的 RSL 数据，以寻找冰。模型和一维地幔粘度模型可以更好地解释这些近场和远场站点的 RSL 数据以及 GRACE 数据，并测试从地震模型导出的 3-D 地幔粘度和板块边界粘度对 GIA 可观测值的影响。任务 3 是检查非牛顿粘度对 GIA 过程模拟的影响，表征近场位置的准 L 形 RSL 曲线，以了解就冰消历史和非牛顿粘度而言，准 L 形 RSL 曲线的成因，并检验非牛顿粘度的影响在 RSL 观测中明显的假设。该奖项反映了 NSF 的法定使命，并已通过使用基金会的智力优点和更广泛的影响审查标准进行评估，认为值得支持。