NSFGEO-NERC: Adjoint tomography of mantle viscosity using deglacial sea level observations

NSFGEO-NERC：利用冰消海平面观测进行地幔粘度的伴随断层扫描

• 批准号: 2002352
• 负责人: Jacqueline Austermann
• 金额: $ 40.8万
• 依托单位: Columbia University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2020
• 资助国家: 美国
• 起止时间: 2020-06-15 至 2023-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2002352&HistoricalAwards=false
• 关键词: NSFGEO; NERC; Adjoint; tomography; mantle

Future sea level change in response to ongoing warming is of societal concern. Adapting to rising seas is a pressing challenge for public health, coastal infrastructure, and economic stability. Sea level today and in the past changes due to the addition of meltwater to the ocean basins, but also due to uplift or sinking of coastlines. One reason for the warping of Earth’s surface is that major ice sheets during the last glacial maximum have pressed down on Earth’s surface and released it as they melt. The investigators will use computational modeling to simulate how sea level and the solid Earth change in response to changing ice sheets over the past 25,000 years when Earth transitioned out of a glacial maximum. To calibrate their model, the team compares their predictions to more than 13,000 sea level observations from the geologic record. That allows them to improve the model and in particular better understand Earth’s internal viscosity, which is a key parameter in these sea level models. This work will allow the team to answer fundamental questions about how fast or slowly Earth’s interior deforms, but also how much solid Earth deformation contributes to sea level change along coastlines today. This is particularly relevant for cities along the U.S. East and West coast in which solid Earth deformation contributes a similar amount of sea level rise compared to warming oceans and melting ice sheets. This project will train two postdoctoral research scientists and one graduate student in an international and highly interdisciplinary setting to understand Earth's internal structure, its climatic history and the pace and magnitude of global change.The viscosity of Earth's mantle varies radially and laterally as a result of its complex thermal structure. While it is known from seismology, geodynamics, mineral physics, and sea level observations that these variations exist, they are difficult to constrain. Through glacial isostatic adjustment (GIA) -- the viscoelastic response of the Earth to waxing and waning ice sheets -- this incomplete knowledge propagates into questions of past ice sheets and sea level change. This proposal constitutes an effort to better understand Earth rheology and its implications for cryosphere evolution. The novel aspect proposed here is to invert sea level, geodetic, and gravitational observations for rheology and deglacial ice sheet changes using gradient-based optimization. Model gradients will be efficiently calculated using the adjoint method. This framework allows the investigators to move beyond a limited set of forward simulations and enables them for the first time to efficiently assimilate sea level data and other GIA observations into a 3D GIA model. The international team will use a newly compiled dataset with over 13,000 datapoints of deglacial sea level to produce the first tomographic image of Earth's internal viscosity structure. They will furthermore use this approach to produce ice sheet reconstructions that are consistent with 3D Earth models. In addition to exploring trade-offs between the Earth and ice structure, the team will develop and implement second-order adjoint equations to assess uncertainty propagation. The model output will allow the investigators to address two targeted research questions, (1) the amount of melt or re-advance of different ice sheets during the Holocene and (2) the present-day contribution of GIA and its uncertainty to sea level change in major coastal cities.This is a project that is jointly funded by the National Science Foundation’s Directorate of Geosciences (NSF/GEO) and the National Environment Research Council (UKRI/NERC) of the United Kingdom (UK) via the NSF/GEO-NERC Lead Agency Agreement. This Agreement allows a single joint US/UK proposal to be submitted and peer-reviewed by the Agency whose investigator has the largest proportion of the budget. Upon successful joint determination of an award, each Agency funds the proportion of the budget and the investigators associated with its own investigators and component of the work.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.

未来海平面变化对持续变暖的反应是社会关注的问题。适应海平面上升是公共卫生、沿海基础设施和经济稳定面临的紧迫挑战。今天和过去的海平面变化是由于海洋盆地的融水增加，也是由于海岸线的隆起或下沉。地球表面弯曲的一个原因是，在最后一次冰川盛期，主要的冰盖压在地球表面上，并在融化时释放出来。研究人员将使用计算模型来模拟海平面和固体地球如何变化，以应对过去25，000年来地球从冰川最大期过渡出来时不断变化的冰盖。为了校准他们的模型，该团队将他们的预测与地质记录中的13，000多个海平面观测结果进行了比较。这使他们能够改进模型，特别是更好地了解地球的内部粘度，这是这些海平面模型的关键参数。这项工作将使研究小组能够回答有关地球内部变形的速度有多快或多慢的基本问题，以及固体地球变形对当今沿着海岸线的海平面变化的贡献。这对于美国东西海岸沿着的城市尤其重要，在这些城市中，与海洋变暖和冰盖融化相比，固体地球变形造成的海平面上升量相似。 该项目将在国际和高度跨学科的环境中培训两名博士后研究科学家和一名研究生，以了解地球的内部结构、气候历史以及全球变化的速度和幅度，由于地球地幔复杂的热结构，地幔的粘性在径向和横向上都有变化。 虽然从地震学、地球动力学、矿物物理学和海平面观测中知道这些变化存在，但它们很难限制。通过冰川均衡调整（GIA）--地球对冰盖变大和变小的粘弹性反应--这种不完整的知识传播到过去冰盖和海平面变化的问题中。这一建议是为了更好地了解地球流变学及其对冰冻圈演变的影响。这里提出的新的方面是反演海平面，大地测量和重力观测的流变学和冰消冰盖的变化，使用基于梯度的优化。使用伴随方法将有效地计算模型梯度。该框架使研究人员能够超越有限的正演模拟，并使他们能够首次有效地将海平面数据和其他GIA观测数据同化到3D GIA模型中。该国际团队将使用一个新编制的数据集，其中包含超过13，000个冰消期海平面数据点，以产生地球内部粘度结构的第一个断层图像。他们还将使用这种方法来制作与3D地球模型一致的冰盖重建。除了探索地球和冰结构之间的权衡之外，该团队还将开发和实现二阶伴随方程，以评估不确定性传播。模型输出将允许研究人员解决两个有针对性的研究问题，（1）全新世期间不同冰盖的融化量或再推进量;（2）GIA的现今贡献及其对主要沿海城市海平面变化的不确定性。这是一个由美国国家科学基金会地球科学理事会（NSF/GEO）共同资助的项目和英国（UK）国家环境研究理事会（UKRI/NERC）通过NSF/GEO-NERC牵头机构协议。该协议允许美国/英国提交一份联合提案，并由研究者拥有最大预算比例的机构进行同行评审。一旦成功地共同确定了一个奖项，每个机构都会为预算的一部分和与自己的调查人员和工作组成部分相关的调查人员提供资金。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

项目成果

Postglacial relative sea level change in Norway

• DOI: 10.1016/j.quascirev.2022.107422
• 发表时间: 2022-03-15
• 期刊: QUATERNARY SCIENCE REVIEWS
• 影响因子: 4
• 作者: Creel, Roger C.;Austermann, Jacqueline;Menke, William
• 通讯作者: Menke, William