Annual Satellite Era Accumulation Patterns Over WAIS Divide: A Study Using Shallow Ice Cores, Near-Surface Radars and Satellites

Abstract: This award supports a project to broaden the knowledge of annual accumulation patterns over the West Antarctic Ice Sheet by processing existing near-surface radar data taken on the US ITASE traverse in 2000 and by gathering and validating new ultra/super-high-frequency (UHF) radar images of near surface layers (to depths of ~15 m), expanding abilities to monitor recent annual accumulation patterns from point source ice cores to radar lines. Shallow (15 m) ice cores will be collected in conjunction with UHF radar images to confirm that radar echoed returns correspond with annual layers, and/or sub-annual density changes in the near-surface snow, as determined from ice core stable isotopes. This project will additionally improve accumulation monitoring from space-borne instruments by comparing the spatial-radar-derived-annual accumulation time series to the passive microwave time series dating back over 3 decades and covering most of Antarctica. The intellectual merit of this project is that mapping the spatial and temporal variations in accumulation rates over the Antarctic ice sheet is essential for understanding ice sheet responses to climate forcing. Antarctic precipitation rate is projected to increase up to 20% in the coming century from the predicted warming. Accumulation is a key component for determining ice sheet mass balance and, hence, sea level rise, yet our ability to measure annual accumulation variability over the past 5 decades (satellite era) is mostly limited to point-source ice cores. Developing a radar and ice core derived annual accumulation dataset will provide validation data for space-born remote sensing algorithms, climate models and, additionally, establish accumulation trends. The broader impacts of the project are that it will advance discovery and understanding within the climatology, glaciology and remote sensing communities by verifying the use of UHF radars to monitor annual layers as determined by visual, chemical and isotopic analysis from corresponding shallow ice cores and will provide a dataset of annual to near-annual accumulation measurements over the past ~5 decades across WAIS divide from existing radar data and proposed radar data. By determining if temporal changes in the passive microwave signal are correlated with temporal changes in accumulation will help assess the utility of passive microwave remote sensing to monitor accumulation rates over ice sheets for future decades. The project will promote teaching, training and learning, and increase representation of underrepresented groups by becoming involved in the NASA History of Winter project and Thermochron Mission and by providing K-12 teachers with training to monitor snow accumulation and temperature here in the US, linking polar research to the student's backyard. The project will train both undergraduate and graduate students in polar research and will encouraging young investigators to become involved in careers in science. In particular, two REU students will participate in original research projects as part of this larger project, from development of a hypothesis to presentation and publication of the results. The support of a new, young woman scientist will help to increase gender diversity in polar research.

摘要：本资助项目旨在通过处理2000年美国ITASE考察队获取的现有近地表雷达数据，以及采集并验证近地表层（深度约15米）的超高频/甚高频（UHF）雷达图像，拓展对西南极冰盖（West Antarctic Ice Sheet, WAIS）年度积累模式的认知范围，将近地表年度积累模式的监测能力从单点冰芯拓展至雷达测线范畴。本项目将结合超高频雷达图像采集浅层（15米）冰芯，通过冰芯稳定同位素分析，验证雷达回波是否与近地表积雪的年层或次年度密度变化相对应。此外，本项目将对比空间雷达反演的年度积累时间序列与覆盖南极绝大多数区域、追溯至30余年前的被动微波时间序列，以此优化星载仪器的积累监测能力。本项目的学术价值在于：绘制南极冰盖积累速率的时空变化图谱，是理解冰盖对气候强迫响应的核心前提。据预测，未来百年内南极降水速率将因气候变暖提升至多20%。积累量是确定冰盖质量平衡、进而评估海平面上升的关键参数，但在过去50年的卫星时代，我们对年度积累变异性的监测能力大多局限于单点冰芯。通过雷达与冰芯获取的年度积累数据集，将为星载遥感算法、气候模型提供验证数据，同时确立区域积累趋势。本项目的拓展影响体现在两方面：其一，通过验证超高频雷达可依托对应浅层冰芯的视觉、化学与同位素分析结果监测年层，推动气候学、冰川学与遥感学界的研究发现与认知深化；其二，将利用现有雷达数据与拟采集的雷达数据，构建过去约50年间西南极冰盖分水岭区域的年度至近年度积累测量数据集。通过探究被动微波信号的时序变化是否与积累量的时序变化相关，将有助于评估被动微波遥感在未来数十年内监测冰盖积累速率的应用潜力。本项目将推动教学、培训与学习活动，并通过参与NASA"冬季史"项目与热年代任务（Thermochron Mission），以及为K-12阶段教师提供培训以监测美国本土的积雪积累与温度，将极地研究与学生的日常环境相联系，提升弱势背景群体的参与度。本项目将培养本科生与研究生的极地研究能力，鼓励青年研究者投身科学事业。具体而言，将有两名大学生研究体验项目（Research Experiences for Undergraduates, REU）学生参与原创性研究项目，全程参与从假说构建到结果展示与发表的全流程。资助一位新兴青年女性科学家，将有助于提升极地研究领域的性别多样性。