Collaborative Research: Tidal Modulation of Ice Stream Flow

该奖项支持一个项目，调查新发现的两个主要南极西部冰流对潮汐振荡的惊人敏感性，以了解这种影响的程度和特征及其对未来冰流行为的影响。冰流D， C和Whillans (B)都显示出强烈而明显的潮汐信号。威兰斯的冰平原通常是完全停止的，前进的运动仅限于每天两个短暂的时期，即涨潮和退潮。运动事件以地震波速度在冰平原上传播。在D河口附近，潮汐导致冰流速度的日变化约为50%，在冰川上传播的速度比在Whillans慢，地震数据表明C经历了更慢的潮汐信号在冰川上的传播。在C冰川上游100多公里处观测到潮汐影响，在D冰川上游40多公里处观测到潮汐影响，可能是在惠兰斯冰川上游400公里处（几乎是冰流的全长）报告的基础水压波动的原因。在第一年，这种行为的空间范围将在Whillans冰流和冰流D上通过五个协调的地震和GPS仪器包在每个冰流上间隔100公里进行测量。这些组件将由“双水獭”在卫星图像审查后选定的地点部署，并将通过太阳能和电池的组合自主运行两个月球周期，以研究冰流运动对春季和小潮的敏感性。此外，现有的数据集将进一步研究所涉及的机制的线索，并将开发初步模型来调和在冰流上观察到的看似相反的行为。第二和第三个野外季节将更详细地检查Whillans（第二年）和D（第三年）的潮汐行为。工作将特别侧重于详细研究至少一个Whillans事件的源区域，假设从初步数据推断的源区域仍然活跃。垂直运动还没有被检测到，但差分GPS将提高我们的检测灵敏度。地震仪器将大大提高时间分辨率和测量传播速度和任何空间非均质性的能力。随着从现场实验中学习到更多的知识，建模将得到改进。该项目将产生许多更广泛的影响。这项研究提高了对冰流行为的认识，将有助于评估影响全球海平面和社会后果的冰盖快速变化的可能性。研究结果将通过科学出版物和专业会议上的演讲、与新闻界的接触、私人顾问教授的大学课程、访问学校和社区团体以及其他活动来传播。通过该项目将培养两名研究生。

This award supports a project to investigate the new-found, startling sensitivity of two major West Antarctic ice streams to tidal oscillations to learn the extent and character of the effect and its ramifications for future ice-stream behavior. Ice streams D, C and Whillans (B) all show strong but distinct tidal signals. The ice plain of Whillans is usually stopped outright, forward motion being limited to two brief periods each day, at high tide and on the falling tide. Motion events propagate across the ice plain at seismic wave velocities. Near the mouth of D, tides cause a diurnal variation of about 50% in ice-stream speed that propagates upglacier more slowly than on Whillans, and seismic data show that C experiences even slower upglacier propagation of tidal signals. Tidal influences are observed more than 100 km upglacier on C, more than 40 km upglacier on D, and may be responsible for fluctuations in basal water pressure reported 400 km upstream on Whillans, nearly the full length of the ice stream. During the first year, the spatial extent of this behavior will be measured on Whillans Ice Stream and ice stream D by five coordinated seismic and GPS instrument packages at 100-km spacing on each ice stream. These packages will be deployed by Twin Otter at sites selected by review of satellite imagery and will operate autonomously through a combination of solar and battery power for two lunar cycles to study the sensitivity of the ice stream motion to spring and neap tides. Additionally, existing data sets will be examined further for clues to the mechanisms involved, and preliminary models will be developed to reconcile the seemingly contrasting behaviors observed on the ice streams. The second and third field seasons will examine in greater detail the tidal behavior of Whillans (year 2) and D (year 3). Work will especially focus on detailed study of at least one source area for events on Whillans, assuming that source areas inferred from preliminary data remain active. Vertical motions have not yet been detected, but differential GPS will increase our detection sensitivity. Seismic instrumentation will greatly increase temporal resolution and the ability to measure the propagation speed and any spatial heterogeneity. Modeling will be refined as more is learned from the field experiments. The project should yield numerous broader impacts. The improved knowledge of ice-stream behavior from this study will contribute to assessment of the potential for rapid ice-sheet change affecting global sea level with societal consequences. Results will be disseminated through scientific publication and talks at professional meetings, as well as contacts with the press, university classes taught by the PIs, visits to schools and community groups, and other activities. Two graduate students will be educated through the project.