Laser Dust Logging of a South Pole Ice Core

This award supports the deployment and analysis of data from an oriented laser dust logger in the South Pole ice core borehole to complement study of the ice core record. Before the core is even processed, data from the borehole probe will immediately determine the depth-age relationship, augment 3D mapping of South Pole stratigraphy, aid in searches for the oldest ice in Antarctica, and reveal layers of volcanic or extraterrestrial fallout. Regarding the intellectual merit, the oriented borehole log will be essential for investigating features in the ice sheet that may have implications for ice core chronology, ice flow, ice sheet physical properties and stability in response to climate change. The tools and techniques developed in this program have applications in glaciology, biogeoscience and exploration of other planetary bodies. The program aims for a deeper understanding of the consequences and causes of abrupt climate change. The broader impacts of the project are that it will include outreach and education, providing a broad training ground for students and post-docs. Data and metadata will be made available through data centers and repositories such as the National Snow and Ice Data Center web portal.

The laser dust logger detects reproducible paleoclimate features at sub-centimeter depth scale. Dust logger data are being used for synchronizing records and dating any site on the continent, revealing accumulation anomalies and episodes of rapid ice sheet thinning, and discovering particulate horizons of special interest. In this project we will deploy a laser dust logger equipped with a magnetic compass to find direct evidence of preferentially oriented dust. Using optical scattering measurements from IceCube calibration studies at South Pole and borehole logs at WAIS Divide, we have detected a persistent anisotropy correlated with flow and crystal fabric which suggests that the majority of insoluble particulates must be located within ice grains. With typical concentrations of parts-per-billion, little is known about the location of impurities within the polycrystalline structure of polar ice. While soluble impurities are generally thought to concentrate at inter-grain boundaries and determine electrical conductivity, the fate of insoluble particulates is much less clear, and microscopic examinations are extremely challenging. These in situ borehole measurements will help to unravel intimate relationships between impurities, flow, and crystal fabric. Data from this project will further develop a unique record of South Pole surface roughness as a proxy for paleowind and provide new insights for understanding glacial radar propagation. This project has field work in Antarctica.

本项目资助部署并分析南极冰芯钻孔定向激光粉尘记录仪（oriented laser dust logger）所采集的数据，以辅助冰芯记录的相关研究。在冰芯完成处理前，钻孔探头采集的数据即可直接确定深度-年代关系，完善南极地层的三维测绘工作，助力南极最古老冰体的搜寻，并揭示火山或地外沉降物层。就学术价值而言，定向钻孔测井数据对于研究冰盖特征至关重要，这些特征或可揭示冰芯年代学、冰流运动、冰盖物理特性以及其对气候变化的响应稳定性等方面的相关信息。本项目开发的工具与技术可应用于冰川学、生物地球科学以及其他天体的探测研究。本项目旨在深入理解气候突变的成因与影响。本项目的社会推广价值包括科普教育工作，为学生与博士后研究人员提供广阔的实践训练平台。项目产生的数据与元数据将通过国家冰雪数据中心（National Snow and Ice Data Center）门户网站等数据中心与存储库公开共享。

激光粉尘记录仪可在亚厘米级深度尺度上识别可重复的古气候特征。粉尘记录仪数据可用于同步各记录序列，并为南极大陆任意点位建立年代标尺，同时可揭示积累异常事件与冰盖快速减薄过程，并发现具有特殊研究价值的微粒层位。本项目将部署搭载磁罗盘的激光粉尘记录仪，以获取粉尘定向排列的直接证据。借助南极冰立方（IceCube）校准研究的光学散射测量数据以及西南极冰盖分水岭（WAIS Divide）的钻孔测井资料，我们已检测到与冰流运动及晶体组构相关的持续性各向异性特征，这表明绝大多数不溶性微粒应位于冰晶粒内部。由于不溶性微粒的典型浓度仅为十亿分之一级，目前学界对极地冰多晶结构中杂质的分布位置仍知之甚少。尽管学界普遍认为可溶性杂质会富集于晶界处并决定冰体的导电性，但不溶性微粒的赋存状态仍不甚明确，且相关显微观测工作极具挑战性。这些原位钻孔测量数据将有助于厘清杂质、冰流与晶体组构之间的内在关联。本项目采集的数据将进一步构建南极地表粗糙度的独有记录，以此作为古风速的代用指标，并为理解冰川雷达传播机制提供新的认识。本项目将在南极开展野外实地工作。