NSF-NERC: THwaites Offshore Research (THOR)

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. Satellite observations extending over the last 25 years show that Thwaites Glacier is rapidly thinning and accelerating. Over this same period, the Thwaites grounding line, the point at which the glacier transitions from sitting on the seabed to floating, has retreated. Oceanographic studies demonstrate that the main driver of these changes is incursion of warm water from the deep ocean that flows beneath the floating ice shelf and causes basal melting. The period of satellite observation is not long enough to determine how a large glacier, such as Thwaites, responds to long-term and near-term changes in the ocean or the atmosphere. As a result, records of glacier change from the pre-satellite era are required to build a holistic understanding of glacier behavior. Ocean-floor sediments deposited at the retreating grounding line and further offshore contain these longer-term records of changes in the glacier and the adjacent ocean. An additional large unknown is the topography of the seafloor and how it influences interactions of landward-flowing warm water with Thwaites Glacier and affects its stability. Consequently, this project focuses on the seafloor offshore from Thwaites Glacier and the records of past glacial and ocean change contained in the sediments deposited by the glacier and surrounding ocean. Uncertainty in model projections of the future of Thwaites Glacier will be significantly reduced by cross-disciplinary investigations seaward of the current grounding line, including extracting the record of decadal to millennial variations in warm water incursion, determining the pre-satellite era history of grounding-line migration, and constraining the bathymetric pathways that control flow of warm water to the grounding line. Sedimentary records and glacial landforms preserved on the seafloor will allow reconstruction of changes in drivers and the glacial response to them over a range of timescales, thus providing reference data that can be used to initiate and evaluate the reliability of models. Such data will further provide insights on the influence of poorly understood processes on marine ice sheet dynamics. This project will include an integrated suite of marine and sub-ice shelf research activities aimed at establishing boundary conditions seaward of the Thwaites Glacier grounding line, obtaining records of the external drivers of change, improving knowledge of processes leading to collapse of Thwaites Glacier, and determining the history of past change in grounding line migration and conditions at the glacier base. These objectives will be achieved through high-resolution geophysical surveys of the seafloor and analysis of sediments collected in cores from the inner shelf seaward of the Thwaites Glacier grounding line using ship-based equipment, and from beneath the ice shelf using a corer deployed through the ice shelf via hot water drill holes. 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.

本项目响应美国国家科学基金会（U.S. National Science Foundation, NSF）与英国自然环境研究理事会（U.K. Natural Environment Research Council, NERC）联合发起的倡议，旨在大幅改进对源自西南极洲思韦茨冰川（Thwaites Glacier）的冰量损失与海平面上升的十年及更长期预测。
过去25年的卫星观测数据显示，思韦茨冰川正快速变薄且流速显著加快。同期，冰川从海底基岩过渡至漂浮状态的接地冰线（grounding line）正持续后退。海洋学研究表明，此类变化的主要驱动因素为深海暖水侵入漂浮冰架下方，引发冰架底部消融。
现有卫星观测的时长不足以明确思韦茨这类大型冰川对海洋与大气的长期、近期变化会作出何种响应。因此，亟需借助卫星时代前的冰川变化记录，以全面理解冰川行为规律。在持续后退的接地冰线外侧及更远近海区域沉积的海底沉积物，留存了冰川与邻近海域长期变化的相关记录。此外，海底地形及其如何影响向陆流动的暖水与思韦茨冰川的相互作用、进而影响冰川稳定性，仍是一项尚未明确的重大科学问题。
有鉴于此，本项目聚焦思韦茨冰川外侧的海底区域，以及冰川与周边海洋沉积所留存的过去冰川与海洋变化记录。
通过对当前接地冰线外侧海域开展跨学科研究——包括提取暖水侵入的十年至千年尺度变化记录、明确卫星时代前的接地冰线迁移历史、约束控制暖水流入侵接地冰线的海底地形（bathymetric）通道——可大幅降低思韦茨冰川未来预测模型的不确定性。
保存在海底的沉积记录与冰川地貌，可帮助重建不同时间尺度下冰川变化的驱动因素及冰川响应过程，从而为模型构建与可靠性评估提供基准参考数据。此类数据还可进一步阐明当前认知不足的过程对海洋冰盖（marine ice sheet）动力学的影响。
本项目将整合一系列冰架下与海洋科考活动，旨在确定思韦茨冰川接地冰线外侧的边界条件，获取冰川变化的外部驱动因素记录，加深对思韦茨冰川崩塌过程的理解，并明确接地冰线迁移与冰川底部环境的历史变化过程。
上述目标将通过以下方式实现：利用科考船搭载设备对思韦茨冰川接地冰线外侧的内陆架区域开展高分辨率地球物理勘测（geophysical surveys）并分析采集的沉积物岩芯（sediment cores），同时借助热水钻孔技术在冰架下方部署取芯设备以获取岩芯样本。
本次资助符合美国国家科学基金会的法定使命，且通过基金会的学术价值与更广泛影响评审标准评估，被认定为值得支持的项目。