Collaborative Research: Antarctic Airborne ElectroMagnetics (ANTAEM) - Revealing Subsurface Water in Coastal Antarctica

在南极洲，数百万年的冰冻导致了数百米厚的永久冻土(即冻土)的发育。最近的研究表明，这种缓慢的冻结将水聚集到当地和地区的咸水层中，比海水的含盐量高出许多倍。因为盐会降低水的冰点，所以这些盐水能够在远低于淡水正常冰点的温度下以液态水的形式存在。这种不同寻常的地下水系统可能支持微生物生命，为沿海海洋和冰盖湖泊提供养分，并影响冰川的运动。这些咸水含水层也是其他行星(如火星)上深层生命栖息地的潜在陆地类似物，并为寻找地外水提供了试验场。虽然人们在了解极地寒冷地区地表和近地表水域的物理、化学和生物学方面投入了大量的努力，但在这种情况下研究深层地下含水层却相对困难。航空电磁法(AEM)地下成像为咸水测绘提供了一种有效的方法。与丹麦奥胡斯大学的国际合作将使AEM技术方面的知识和技能转移成为可能，这将增强美国的极地研究能力，并为美国本科生和研究生提供独特的培训体验。该项目将对南极洲麦克默多站附近超过1000平方公里的海洋和陆地进行调查，并将揭示寒冷的极地沙漠是否隐藏了地下液态水池。这将对理解寒冷的极地冰川、冰盖的湖泊、冰冻的地面和极地微生物学以及预测它们对未来变化的反应具有重要意义。永冻层测绘技术的改进以及对永冻层和地下地下水的了解将有利于人类对南极和北极高极地区的利用。该项目将首次对南极部分无冰的沿海地区麦克默多干谷的地下水分布和水文连通性进行系统规模的综合概述。液态水在这种环境中相对稀缺，但通过影响和整合生物、生物地球化学、冰川和地质过程，发挥着巨大的作用。尽管地表水文学及其在生态系统过程中的作用在过去几十年中得到了彻底的研究，但很难绘制和描述地下水库的特征，也很难理解它们与区域湖泊、冰川和沿海水域的相互作用。拟议的项目建立在2011年使用AEM技术的“概念验证”的基础上。与2011年的概念验证调查相比，传感器和数据处理能力的改进将使新数据收集期间地下的渗透深度增加约一倍，后者达到300-400米的深度。第一个野外季节将侧重于在以下关键地点利用地面系统收集深度测深：(I)过去钻探项目对地下结构的独立限制，以及(Ii)2011年的电阻率数据集表明，需要更深的渗透率和只有地面系统才能实现的高信噪比。区域航空调查将在第二个野外季节进行，将产生不同大小和不同冰盖比例的几个山谷的地下电阻率数据。

In Antarctica, millions of years of freezing have led to the development of hundreds of meters of thick permafrost (i.e., frozen ground). Recent research demonstrated that this slow freezing has trapped and concentrated water into local and regional briny aquifers, many times more salty than seawater. Because salt depresses the freezing point of water, these saline brines are able to persist as liquid water at temperatures well below the normal freezing point of freshwater. Such unusual groundwater systems may support microbial life, supply nutrients to coastal ocean and ice-covered lakes, and influence motion of glaciers. These briny aquifers also represent potential terrestrial analogs for deep life habitats on other planets, such as Mars, and provide a testing ground for the search for extraterrestrial water. Whereas much effort has been invested in understanding the physics, chemistry, and biology of surface and near-surface waters in cold polar regions, it has been comparably difficult to investigate deep subsurface aquifers in such settings. Airborne ElectroMagnetics (AEM) subsurface imaging provides an efficient way for mapping salty groundwater. An international collaboration with the University of Aarhus in Denmark will enable knowledge and skill transfer in AEM techniques that will enhance US polar research capabilities and provide US undergraduates and graduate students with unique training experiences. This project will survey over 1000 km2 of ocean and land near McMurdo Station in Antarctica, and will reveal if cold polar deserts hide a subsurface pool of liquid water. This will have significant implications for understanding cold polar glaciers, ice-covered lakes, frozen ground, and polar microbiology as well as for predictions of their response to future change. Improvements in permafrost mapping techniques and understanding of permafrost and of underlying groundwaters will benefit human use of high polar regions in the Antarctic and the Arctic.The project will provide the first integrative system-scale overview of subsurface water distribution and hydrological connectivity in a partly ice-free coastal region of Antarctica, the McMurdo Dry Valleys. Liquid water is relatively scarce in this environment but plays an outsized role by influencing, and integrating, biological, biogeochemical, glaciological, and geological processes. Whereas surface hydrology and its role in ecosystem processes has been thoroughly studied over the last several decades, it has been difficult to map out and characterize subsurface water reservoirs and to understand their interactions with regional lakes, glaciers, and coastal waters. The proposed project builds on the "proof-of-concept" use of AEM technology in 2011. Improvements in sensor and data processing capabilities will result in about double the depth of penetration of the subsurface during the new data collection when compared to the 2011 proof-of-concept survey, which reached depths of 300-400m. The first field season will focus on collecting deep soundings with a ground-based system in key locations where: (i) independent constraints on subsurface structure exist from past drilling projects, and (ii) the 2011 resistivity dataset indicates the need for deeper penetration and high signal-to-noise ratios achievable only with a ground-based system. The regional airborne survey will take place during the second field season and will yield subsurface electrical resistivity data from across several valleys of different sizes and different ice cover fractions.