NSF-NERC: Geological History Constraints on the Magnitude of Grounding Line Retreat in the Thwaites Glacier System

该项目为美国国家科学基金会(NSF)和英国自然环境研究理事会(NERC)发起的联合倡议做出了贡献，该倡议旨在大幅改善对南极洲西部斯韦茨冰川造成的冰流失和海平面上升的十年和更长期的预测。斯韦茨冰川系统是南极洲海平面上升的主要原因。预测这个系统在未来几十年将如何演变，从而可能对海平面做出贡献，需要详细了解它过去如何应对气候和海洋条件的变化。该项目将通过建立抬高的海洋海滩的年表，以及通过冰下钻探对目前由Thwaites冰川覆盖的基岩进行采样和测年，来记录过去10,000年来Thwaites冰川退缩的时间和持续时间，从而记录区域海平面的变化。与来自其他记录的气候和海洋条件一起，这些将为过去到现在的模型模拟以及用于预测一系列气候情景下未来冰川变化的边界条件提供边界条件。具体地说，该项目将检验该地区现有地质证据所暗示的假设，即目前斯韦茨冰川系统的快速消退是可逆的。该团队的目标是利用两种方法：1.为了重建全新世的相对海平面，他们将绘制整个松岛湾上升的海洋和海岸线沉积物的地图并确定日期。对地貌和沉积物中与过去海平面遗传相关的有机物质，如贝壳碎片、海洋动物骨骼和企鹅鸟粪进行放射性碳测年，将提供海平面变化的年代学限制。2.为了获得过去接地线退缩事件的地质证据，该小组将对冰下基岩进行宇宙源核素暴露测年。使用最近开发的用于冰下基岩恢复的钻探系统，该团队将从冰层厚度与Thwaites系统中的接地线位置动态联系的地点(特别是在哈德逊山脉和墨菲山附近)获取冰下基岩。观测到重要的宇宙源核素浓度--该团队将主要测量这些样本中的铍-10和原位碳-14--将为过去与接地线后退有关的变薄事件提供直接、明确的证据，以及对其时间和持续时间的限制。这一裁决反映了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。

This project contributes to the joint initiative launched by the U.S. National Science Foundation (NSF) and the U.K. Natural Environment Research Council (NERC) to substantially improve decadal and longer-term projections of ice loss and sea-level rise originating from Thwaites Glacier in West Antarctica. The Thwaites Glacier system dominates the contribution to sea-level rise from Antarctica. Predicting how this system will evolve in coming decades, and thereby its likely contribution to sea level, requires detailed understanding of how it has responded to changes in climate and oceanographic conditions in the past. This project will provide a record of regional sea-level change by establishing chronologies for raised marine beaches as well as the timing and duration of periods of retreat of Thwaites Glacier during the past 10,000 years by sampling and dating bedrock presently covered by Thwaites Glacier via subglacial drilling. Together with climatic and oceanographic conditions from other records, these will provide boundary conditions for past-to-present model simulations as well as those used to predict future glacier changes under a range of climate scenarios. Specifically, the project will test the hypothesis--implied by existing geological evidence from the region--that present rapid retreat of the Thwaites Glacier system is reversible. The team aims to utilize two approaches: 1. To reconstruct relative sea level during the Holocene, it will map and date raised marine and shoreline deposits throughout Pine Island Bay. Chronological constraints on sea-level change will be provided by radiocarbon dating of organic material in landforms and sediments that are genetically related to past sea level, such as shell fragments, bones of marine fauna, and penguin guano. 2. To obtain geological evidence for past episodes of grounding-line retreat, the team will apply cosmogenic-nuclide exposure-dating of subglacial bedrock. Using drill systems recently developed for subglacial bedrock recovery, the team will obtain subglacial bedrock from sites where ice thickness is dynamically linked to grounding-line position in the Thwaites system (specifically in the Hudson Mountains, and near Mount Murphy). Observation of significant cosmogenic-nuclide concentrations--the team will primarily measure Beryllium-10 and in situ Carbon-14--in these samples would provide direct, unambiguous evidence for past episodes of thinning linked to grounding-line retreat as well as constraints on their timing and duration.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.