Refining the bounds of Marine Isotope Stage 5a and 5c peak sea level: Insights from 3D modeling of glacial isostatic adjustment

细化海洋同位素阶段 5a 和 5c 峰值海平面的范围：冰川均衡调整 3D 建模的见解

• 批准号: 1927326
• 负责人: Jessica Creveling
• 金额: $ 24.55万
• 依托单位: Oregon State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2019
• 资助国家: 美国
• 起止时间: 2019-09-01 至 2024-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1927326&HistoricalAwards=false
• 关键词: Refining; bounds; Marine; Isotope; Stage

Marine terraces and other geological markers of an ancient ocean's shoreline can constrain the height of sea level for past warm periods with similar or less ice than exists on Earth today. However, geoscientists must be careful to correct for local tectonic displacement and motion of the Earth's crust that arises from the growth and melt of ice sheets when stating that a geological marker's present elevation equals the height of sea level long ago. In the case of the latter, continental ice sheets, like those that existed across Canada and the northern U.S. at the last glacial maximum, loaded down the glaciated crust and created a raised bulge that extended south as far as Florida/Caribbean and southern California/Baja California on the east and west Coasts of North America, respectively. This physics is similar to the deformation caused by a person sitting on a soft mattress. Like the mattress analogy, when continental ice sheets melt (the person stands up), the loaded portion begins to bounce back, or rebound, and the raised portion begins to relax down, or subside. For the Earth's crust, however, the adjustment from being loaded to unloaded takes many, many thousands of years to complete. For this reason, geoscientists use computer models for how Earth's crust deforms to "correct" the elevations of geological markers for past shorelines and therefore determine past sea level heights; by assuming that the Earth has a simple, layered, internal structure, that looks like a concentric jaw-breaker candy in cross-section, geoscientists can model Earth's deformation on a desktop computer. Here the investigator proposes to update this computer model with more realistic lateral and vertical layers of Earth's composition as determined from seismic-wave imaging of Earth's interior (much like an ultrasound). The PI proposes to use more powerful computers to complete this modeling effort. The PI will compare the computer model outputs to a compilation of published elevations of globally distributed marine terraces and geological shoreline markers for two periods of warmth during the last ice age that occurred ~80 and ~100 thousand years ago. This research will refine estimates of global sea level and during these past intervals of ice-age warmth. The proposed research will train a PhD student in sea level research methods; together with the Oregon Museum of Science and Industry (OMSI), the scientists will create a hands-on activity of how geologists use the geological archive of ancient sea level and global geophysical models of Earth's structure to understand the stability of ice sheets during past climate states.Global geophysical models of glacial isostatic adjustment (GIA) utilize the geographic pattern of past sea level reconstructed from marine terraces and other shoreline markers to determine global mean sea level (GMSL), and equivalent ice volume, during past warm periods. A compilation of published elevations of globally distributed markers for Marine Isotope Stage (MIS) 5a and 5c high stands, ~80 and ~100 ka, respectively, offer the opportunity to examine the magnitude of peak GMSL arising from an orbital precession cycle. Recent GIA analyses of regional subsets of this global compilation of geological markers have produced discrepant estimates of MIS 5a and 5c peak GMSL that vary between ~5 to 40 m below present sea level. These analyses adopted independent one-dimensional models of Earth's viscoelastic structure- that is, depth varying but laterally homogenous- that best fit regional subsets of paleo-sea level markers. However, these 1D models could not fit the full suite of geological constraints from around the globe, thus introducing biases into GMSL reconstructions. Here, the investigator propose to adopt a three-dimensional finite element model of GIA that captures both the lateral and radial complexity in Earth's viscoelastic structure as inferred from recent studies of high-resolution seismic shear wave tomography in order to improve the fit between numerical predictions of the geographically variable pattern in sea level arising from GIA and a global compilation of geological indicators of MIS 5a and 5c peak sea level. This exercise will refine estimates of MIS 5a and 5c peak global mean sea level and further constrain cryosphere stability during these past intervals of relative ice-age warmth. As such, the proposed research represents a timely opportunity-and necessary next step- to further our understanding of the magnitude and rate of cryosphere change as evidenced by the geological record. Finally, the results of this project will be directly relevant to ongoing studies of seismic hazard (for example, across the U.S. Pacific coast) through refinements of regional rates of tectonic uplift.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.

海洋阶地和古代海洋海岸线的其他地质标志可以限制过去温暖时期的海平面高度，与今天地球上存在的冰相似或更少。然而，地球科学家必须小心地纠正局部构造位移和地壳运动，这些位移和地壳运动是由冰盖的生长和融化引起的，因为他们认为地质标志物现在的海拔高度等于很久以前的海平面高度。在后一种情况下，大陆冰盖，就像那些存在于加拿大和北方美国的冰盖一样，在末次盛冰期，把冰川地壳压下来，形成了一个隆起，向南延伸到佛罗里达/加勒比海和加州南部/下加利福尼亚分别在北美的东海岸和西海岸。这种物理现象类似于一个人坐在柔软的床垫上引起的变形。就像床垫的比喻一样，当大陆冰盖融化时（人站起来），承载的部分开始反弹，或者反弹，而升高的部分开始放松，或者消退。然而，对于地壳来说，从加载到卸载的调整需要数千年才能完成。由于这个原因，地球科学家使用计算机模型来研究地壳如何变形，以“校正”过去海岸线的地质标志的海拔，从而确定过去的海平面高度;通过假设地球具有简单的分层内部结构，看起来像一个同心圆的糖果横截面，地球科学家可以在台式计算机上模拟地球的变形。在这里，研究人员建议用更真实的地球组成的横向和垂直层来更新这个计算机模型，这些层是从地球内部的地震波成像（很像超声波）中确定的。PI建议使用更强大的计算机来完成这一建模工作。PI将比较计算机模型输出与全球分布的海洋阶地和地质海岸线标记的出版海拔高度汇编，这些海拔高度是发生在大约8万年前和大约10万年前的最后一个冰河时期的两个温暖时期。这项研究将完善全球海平面的估计，并在这些过去的冰河时期温暖的间隔。拟议的研究将培养一名海平面研究方法的博士生;与俄勒冈州科学与工业博物馆（OMSI）一起，科学家们将创建一个实践活动，了解地质学家如何使用古代海平面的地质档案和地球结构的全球地球物理模型来了解过去气候状态下冰盖的稳定性。利用从海洋阶地和其他海岸线标志重建的过去海平面的地理模式，确定过去温暖时期的全球平均海平面（GMSL）和等效冰量。海洋同位素阶段（MIS）5a和5c高的立场，~80和~100 ka，分别公布的全球分布的标记海拔的汇编，提供了机会来检查峰值GMSL产生的轨道岁差周期的幅度。最近GIA对全球地质标志汇编的区域子集进行的分析得出了MIS 5a和5c峰值GMSL的不一致估计，这些峰值在目前海平面以下约5至40 m之间变化。这些分析采用了地球粘弹性结构的独立一维模型--即深度变化但横向均匀--最适合古海平面标志的区域子集。然而，这些1D模型不能适应来自地球仪周围的全套地质约束，从而在GMSL重建中引入偏差。在这里，研究人员建议采用GIA的三维有限元模型，该模型可以捕获地球粘弹性结构中的横向和径向复杂性，这是从最近的高分辨率地震剪切波层析成像，以改善GIA引起的海平面地理变化模式的数值预测与MIS 5a和5c峰的全球地质指标汇编之间的拟合海拔这项工作将完善MIS 5a和5c峰值全球平均海平面的估计，并进一步限制在这些相对冰期温暖的过去间隔期间冰冻圈的稳定性。因此，拟议中的研究代表了一个及时的机会，也是必要的下一步，以进一步了解地质记录所证明的冰冻圈变化的幅度和速度。最后，该项目的成果将直接关系到正在进行的研究地震危险（例如，整个美国太平洋海岸）通过细化区域的构造隆起率。该奖项反映了NSF的法定使命，并已被认为是值得支持的评估使用基金会的知识价值和更广泛的影响审查标准。

项目成果

A global database of marine isotope substage 5a and 5c marine terraces and paleoshoreline indicators

海洋同位素亚阶段 5a 和 5c 海洋阶地和古海岸线指标的全球数据库

• DOI: 10.5194/essd-13-3467-2021
• 发表时间: 2021
• 期刊: Earth System Science Data
• 影响因子: 11.4
• 作者: Thompson, Schmitty B.;Creveling, Jessica R.
• 通讯作者: Creveling, Jessica R.

Three-dimensional glacial isostatic adjustment modeling reconciles conflicting geographic trends in North American marine isotope stage 5a relative sea level observations

三维冰川均衡调整模型协调了北美海洋同位素阶段 5a 相对海平面观测中相互冲突的地理趋势

• DOI: 10.1130/g51257.1
• 发表时间: 2023
• 期刊: Geology
• 影响因子: 5.8
• 作者: Thompson, Schmitty B.;Creveling, Jessica R.;Latychev, Konstantin;Mitrovica, Jerry X.
• 通讯作者: Mitrovica, Jerry X.