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

GSTDTAP

项目编号	1927326
	Refining the bounds of Marine Isotope Stage 5a and 5c peak sea level: Insights from 3D modeling of glacial isostatic adjustment
	Jessica Creveling (Principal Investigator)
主持机构	Oregon State University
项目开始年	2019
	2019-09-01
项目结束日期	2022-08-31
资助机构	US-NSF
项目类别	Standard Grant
项目经费	245474(USD)
国家	美国
语种	英语
英文摘要	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.
文献类型	项目
条目标识符	http://119.78.100.173/C666/handle/2XK7JSWQ/214046
专题	环境与发展全球科技态势
推荐引用方式 GB/T 7714	Jessica Creveling .Refining the bounds of Marine Isotope Stage 5a and 5c peak sea level: Insights from 3D modeling of glacial isostatic adjustment.2019.