NSFGEO-NERC: Collaborative Research: How important are sea-level feedbacks in stabilizing marine-based ice streams?

在对21世纪海平面上升的预测中，最大的不确定性之一是，随着全球气温的上升，格陵兰和南极的冰盖是否会以及如何崩溃。这种不确定性的一个方面涉及固体地球对冰川后反弹形式的冰融化的反应，即在冰的重量被移除后地壳的抬升。这个项目将研究2万年前最后一次冰川盛期覆盖苏格兰西北部的冰盖下地球的行为。在最后一次冰川盛期之后，随着地球变暖，冰盖缩小，大约17,000年前，苏格兰西北部的一部分冰盖经历了一段“崩溃”或快速退缩的时期。这项研究将使用过去海平面的记录来记录地球在这个正在消退的冰盖前面的行为，以确定它的反弹(抬升)速度是否足以帮助稳定正在消退的冰盖。还将进行数值实验，以重现这段时间内地球和冰盖的行为，并将这些模型实验与苏格兰过去海平面变化的测量记录进行比较。这些比较将使人们能够对冰盖退缩的行为有新的见解，并对曾经覆盖苏格兰西北部的冰盖的历史和大小提供更好的约束。该项目将为少数民族人口较多的高中的学生举办为期三周的住校夏令营，向他们介绍地球科学的各个方面。这项研究的目的是调查海平面反馈在海洋冰盖退缩过程中稳定的重要性。拟议的调查将结合新的晚更新世/全新世相对海平面限制条件，从苏格兰西北部的上升海岸线、现有近海海芯和孤立盆地收集，以完善不列颠群岛的冰川均衡调整模型。该提案还将在更局部的层面和晚更新世冰流的规模上调查海平面反馈，该冰流曾使用更专门的冰盖模型流经苏格兰西北部的明奇。该模型与改进的不列颠群岛“全球”尺度冰川均衡调整模型的结果相结合，将被用来理解前Minch冰流对更多局部变量(例如地幔流变性、岩石圈厚度、冰盖几何形状等)的敏感性。将检验三个假设：1.)海平面反馈没有为明奇冰流在最后一次冰川盛期之后的消退过程中提供稳定的影响；沿着凹陷的冰盖边缘，海平面的反馈不是由当地的冰锋决定的，而是由区域均衡调整决定的；海平面反馈对稳定海洋冰流的影响是其下方地球流变学的函数。该奖项反映了NSF的法定使命，并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，被认为值得支持。

Among the largest uncertainties in projections of 21st century sea-level rise is whether and how the Greenland and Antarctic Ice Sheets may collapse as global temperatures increase. One aspect of this uncertainty concerns how the solid Earth responds to melting ice in the form of post-glacial rebound, that is, uplift of crust after the weight of the ice has been removed. This project will examine the behavior of the Earth beneath the ice sheet that covered northwest Scotland during the Last Glacial Maximum, 20,000 years ago. As the earth warmed following the Last Glacial Maximum the ice sheet shrank and around 17,000 years ago a portion of the ice sheet over northwest Scotland experienced a “collapse” or period of fast retreat. The research will use records of past sea levels to document the behavior of the Earth beneath the front of this retreating ice sheet to determine if it rebounded (uplifted) fast enough to help stabilize the retreating ice sheet. There will also be numerical experiments to recreate the behavior of the Earth and ice sheet during this time period and compare these model experiments with measured records of past sea level changes across Scotland. These comparisons will permit new insights into the behavior of retreating ice sheets and provide better constraints on the history and size of the ice sheet that once covered northwest Scotland. The project will conduct a three-week in-residence summer camp for students from high schools with large minority populations to introduce them to the varied dimensions of Earth Science. The purpose of this research is to investigate the importance of sea-level feedbacks in stabilizing marine-based ice sheets during their retreat. The proposed investigation will combine new late Pleistocene/Holocene relative sea-level constraints to be collected from raised shorelines, existing offshore marine cores, and isolation basins from across northwestern Scotland, to refine the glacial isostatic adjustment models for the British Isles. The proposal will also investigate sea-level feedbacks at a more local level and at the scale of the Late Pleistocene ice stream that once flowed through the Minch of northwestern Scotland using a more specialized ice-sheet model. This model, coupled with results from an improved “global” scale glacial isostatic adjustment model for the British Isles, will be used to understand the sensitivity of the former Minch ice stream to more local variables (e.g. mantle rheology, lithospheric thickness, ice sheet geometry, etc.). Three hypotheses will be tested: 1.) Sea-level feedback did not provide a stabilizing influence for the Minch Ice Stream during its retreat following the Last Glacial Maximum; 2.) along indented ice-sheet margins, sea-level feedbacks are governed not by the local ice front but by regional isostatic adjustment; and 3.) the influence of sea-level feedback in stabilizing marine ice streams is a function of the rheology of the Earth beneath it.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.