NSF-NERC: THwaites Offshore Research (THOR)

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。过去25年的卫星观测表明，斯韦茨冰川正在迅速变薄和加速。在同一时期，Thwaites接地线--冰川从海床上过渡到漂浮的地方--已经后退。海洋学研究表明，这些变化的主要驱动力是来自深海的温暖水的入侵，这些水在漂浮的冰架下面流动并导致底部融化。卫星观测的时间不够长，不足以确定像Thwaites这样的大型冰川对海洋或大气的长期和近期变化做出的反应。因此，需要记录前卫星时代的冰川变化，以建立对冰川行为的整体理解。在后退的接地线和更远的近海沉积的海底沉积物包含了冰川和邻近海洋变化的长期记录。另外一个巨大的未知数是海底的地形，以及它如何影响向陆地流动的暖水与Thwaites冰川的相互作用，以及如何影响其稳定性。因此，这个项目侧重于Thwaites冰川近海的海底，以及冰川和周围海洋沉积的沉积物中所包含的过去冰川和海洋变化的记录。通过沿当前接地线进行的跨学科调查，将大大减少对Thwaites冰川未来模型预测的不确定性，包括提取暖水入侵的年代变化记录，确定接地线迁移的卫星前时代历史，以及限制控制暖水流向接地线的水深测量路径。保存在海底的沉积记录和冰川地貌将能够在一系列时间尺度上重建驱动因素的变化和冰川对这些变化的响应，从而提供可用于启动和评估模型可靠性的参考数据。这些数据将进一步深入了解知之甚少的过程对海洋冰盖动态的影响。该项目将包括一套综合的海洋和冰架下研究活动，旨在确定Thwaites冰川接地线向海上移动的边界条件，获取变化的外部驱动因素的记录，增进对导致Thwaites冰川崩塌的过程的了解，并确定过去接地线迁移的历史和冰川基地的条件。这些目标将通过对海底进行高分辨率地球物理调查，并使用船基设备从Thwaites冰川基准线向海的内陆架收集的岩芯中收集的沉积物，以及使用通过热水钻探穿过冰架部署的取样器从冰架下方收集的沉积物进行分析来实现。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。

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.