Investigating Effects of Transient and Non-Newtonian Mantle Viscosity on Glacial Isostatic Adjustment Process and their Implications for GPS Observations in Antarctica

研究瞬态和非牛顿地幔粘度对冰川均衡调整过程的影响及其对南极 GPS 观测的影响

• 批准号: 2333940
• 负责人: Shijie Zhong
• 金额: $ 37.76万
• 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: 2024
• 资助国家: 美国
• 起止时间: 2024-01-01 至 2026-12-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2333940&HistoricalAwards=false
• 关键词: Investigating; Effects; Transient; Non; Newtonian

Satellite observations of Earth’s surface gravity and elevation changes indicate rapid melting of ice sheets in recent decades in northern Antarctica Peninsula and Amundsen Sea Embayment of West Antarctica. This rapid melting may lead to significant global sea level rise which is a major societal concern. Measurements from the Global Positioning System (GPS) show rapid land uplift in these regions as the ice sheets melt. When an ice sheet melts, the melt water flows to oceans, causing global sea level to rise. However, the sea level change at a given geographic location is also influenced by two other factors associated with the ice melting process: 1) the vertical motion of the land and 2) gravitational attraction. The vertical motion of the land is caused by the change of pressure force on the surface of the solid Earth. For example, the removal of ice mass reduces the pressure force on the land, leading to uplift of the land below the ice sheet, while the addition of water in oceans increases the pressure force on the seafloor, causing it to subside. The sea level always follows the equipotential surface of the gravity which changes as the mass on the Earth’s surface (e.g., the ice and water) or/and in its interiors (e.g., at the crust-mantle boundary) is redistributed. Additionally, the vertical motion of the land below an ice sheet has important effects on the evolution and stability of the ice sheet and may determine whether the ice sheet will rapidly collapse or gradually stabilize. The main goal of this project is to build an accurate and efficient computer model to study the displacement and deformation of the Antarctic crust and mantle in response to recent ice melting. The project will significantly improve existing and publicly available computer code, CitcomSVE. The horizontal and vertical components of the Earth’s surface displacement depends on mantle viscosity and elastic properties of the Earth. Although seismic imaging studies demonstrate that the Antarctica mantle is heterogeneous, most studies on the ice-melting induced deformation in Antarctica have assumed that mantle viscosity and elastic properties only vary with the depth due to computational limitations. In this project, the new computational method in CitcomSVE avoids such assumptions and makes it possible to include realistic 3-D mantle viscosity and elastic properties in computing the Antarctica crustal and mantle displacement. This project will interpret the GPS measurements of the surface displacements in northern Antarctica Peninsula and Amundsen Sea Embayment of West Antarctica and use the observations to place constraints on mantle viscosity and deformation mechanisms. The project will also seek to predict the future land displacement Antarctica, which will lead to a better understand of Antarctica ice sheets. Finally, the project has direct implications for the study of global sea level change and the dynamics of the Greenland ice sheet. Technical DescriptionGlacial isostatic adjustment (GIA) is important for understanding not only fundamental science questions including mantle viscosity, mantle convection and lithospheric deformation but also societally important questions of global sea-level change, polar ice melting, climate change, and groundwater hydrology. Studies of rock deformation in laboratory experiments, post-seismic deformation, and mantle dynamics indicate that mantle viscosity is temperature- and stress-dependent. Although the effects of stress-dependent (i.e., non-Newtonian) viscosity and transient creep rheology on GIA process have been studied, observational evidence remains elusive. There has been significant ice mass loss in recent decades in northern Antarctica Peninsula (NAP) and Amundsen Sea Embayment (ASE) of West Antarctica. The ice mass loss has caused rapid bedrock uplift as measured by GPS techniques which require surprisingly small upper mantle viscosity of ~1018 Pas. The rapid uplifts may have important feedback effects on ongoing ice melting because of their influence on grounding line migration, and the inferred small viscosity may have implications for mantle rheology and deformation on decadal time scales. The main objective of the project is to test hypotheses that the GPS observations in NAP and ASE regions are controlled by 3-D non-Newtonian or/and transient creep viscosity by developing new GIA modeling capability based on finite element package CitcomSVE. The project will carry out the following three tasks: Task 1 is to build GIA models for the NAP and ASE regions to examine the effects of 3-D temperature-dependent mantle viscosity on the surface displacements and to test hypothesis that the 3-D mantle viscosity improves the fit to the GPS observations. Task 2 is to test the hypothesis that non-Newtonian or/and transient creep rheology controls GIA process on decadal time scales by computing GIA models and comparing model predictions with GPS observations for the NAP and ASE regions. Task 3 is to implement transient creep (i.e., Burgers model) rheology into finite element package CitcomSVE for modeling the GIA process on global and regional scales and to make the package publicly available to the scientific community. The project will develop the first numerical GIA model with Burgers transient rheology and use the models to examine the effects of 3-D temperature-dependent viscosity, non-Newtonian viscosity and transient rheology on GIA-induced surface displacements in Antarctica. The project will model the unique GPS observations of unusually large displacement rates in the NAP and ASE regions to place constraints on mantle rheology and to distinguish between 3-D temperature-dependent, non-Newtonian and transient mantle viscosity. The project will expand the capability of the publicly available software package CitcomSVE for modeling viscoelastic deformation and tidal deformation on global and regional scales. The project will advance our understanding in lithospheric deformation and mantle rheology on decadal time scales, which helps predict grounding line migration and understand ice sheet stability in West Antarctica. The project will strengthen the open science practice by improving the publicly available code CitcomSVE at github.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.

对地球表面重力和海拔变化的卫星观测表明，近几十年来，南极洲半岛北部和西南极洲阿蒙森海湾的冰盖迅速融化，这种快速融化可能导致全球海平面大幅上升，这是一个重大的社会问题。全球定位系统（GPS）显示，随着冰盖融化，这些地区的陆地迅速隆起。当冰盖融化时，融水流入海洋，导致全球海平面上升。给定地理位置的变化还受到与冰融化过程相关的其他两个因素的影响：1）陆地的垂直运动和2）陆地的垂直运动是由作用在冰上的压力的变化引起的。例如，冰块的去除减少了陆地上的压力，导致冰盖下方的陆地隆起，而海洋中水的增加增加了海底的压力，导致冰盖下方的陆地隆起。海平面总是随之下降。随着地球表面（例如冰和水）或/和其内部（例如地壳-地幔边界）的质量在冰盖下方重新分布而变化的重力等位面对冰盖具有重要影响。该项目的主要目标是建立一个准确有效的计算机模型来研究冰盖的位移和变形。该项目将显着改进现有的和公开的计算机代码，CitcomSVE 地球表面位移的水平和垂直分量取决于地球的地幔粘度和弹性特性。成像研究表明，南极洲地幔是不均匀的，大多数关于南极洲冰融化引起的变形的研究都假设地幔粘度和弹性特性仅随深度而变化，因为在该项目中，CitcomSVE 中的新计算方法避免了此类假设，并且可以在计算南极洲地壳和地幔位移时包含真实的 3D 地幔粘度和弹性属性。该项目还将研究南极半岛北部和西南极洲阿蒙森海湾的地表位移，并利用观测结果对地幔粘度和变形机制进行限制。最后，该项目对研究全球海平面变化和格陵兰冰盖的动态具有重要意义。不仅了解地幔粘度、地幔对流和岩石圈变形等基础科学问题，而且了解全球海平面变化、极地冰融化、气候变化和地下水水文学等重要社会问题。实验室实验中的岩石变形、震后变形和地幔动力学表明，地幔粘度与温度和应力有关，尽管应力依赖（即非牛顿）粘度和瞬态蠕变流变学对 GIA 过程的影响已被证实。研究表明，近几十年来，南极洲半岛北部（NAP）和西部阿蒙森海湾（ASE）的冰量明显减少。通过 GPS 技术测量，南极洲的冰块损失导致了基岩的快速抬升，这需要约 1018 Pas 的上地幔粘度。由于它们对接地线迁移的影响，快速抬升可能会对正在进行的冰融化产生重要的影响。推断出的小粘度可能对年代际时间尺度上的地幔流变和变形产生影响。该项目的主要目标是检验 NAP 和 ASE 地区 GPS 观测的假设。通过开发基于有限元软件包 CitcomSVE 的新 GIA 建模功能，由 3-D 非牛顿或/和瞬态蠕变粘度控制。 该项目将执行以下三项任务： 任务 1 是为 NAP 和 ASE 构建 GIA 模型。区域，以检查 3-D 温度相关地幔粘度对表面位移的影响，并检验 3-D 地幔粘度改善与 GPS 观测的拟合的假设。是通过计算 GIA 模型并将模型预测与 NAP 和 ASE 区域的 GPS 观测结果进行比较来测试非牛顿或/和瞬态蠕变流变学在十年时间尺度上控制 GIA 过程的假设。任务 3 是实现瞬态蠕变（即， Burgers 模型）流变学纳入有限元软件包 CitcomSVE，用于在全球和区域尺度上对 GIA 过程进行建模，并向科学界公开该软件包。该项目将开发第一个数值 GIA 模型。 Burgers 瞬态流变学并使用这些模型来研究 3-D 温度依赖性粘度、非牛顿粘度和瞬态流变学对 GIA 引起的南极洲表面位移的影响。该项目将对南极洲异常大的位移率的独特 GPS 观测进行建模。 NAP 和 ASE 区域对地幔流变学进行限制，并区分 3-D 温度依赖性、非牛顿和瞬态地幔粘度。该项目将扩大这一能力。该项目将促进我们对十年时间尺度上的岩石圈变形和地幔流变学的理解，这有助于预测接地线迁移并了解西部冰盖的稳定性。南极洲。该项目将通过改进 github 上的公开代码 CitcomSVE 来加强开放科学实践。该奖项反映了 NSF 的法定使命，并被认为是值得的。通过使用基金会的智力优势和更广泛的影响审查标准进行评估来获得支持。