Mapping Antarctic Subglacial Water in Three Dimensions with Novel Electromagnetic Techniques

南极冰盖被一个动态的水系统所覆盖，该系统为冰流和出口冰川的流动提供润滑剂，为多样化的微生物生态系统提供栖息地，并向南大洋输送淡水和营养物质。然而，很难想象这种冰下环境：南极洲是一块广袤的大陆，冰厚达4公里(2.5英里)。为了探测冰床界面和更深的地下水水库中的水，该项目将采用一种名为电磁测深的技术，这种技术在陆地和海洋中得到了很好的应用，用于对地表下的流体进行成像。据估计，地下水是南极洲冰下水收支的重要组成部分，但以前的观测方法一直无法确定其数量和分布。因此，该项目将提供有关冰-岩石-水-海洋系统如何相互作用的关键信息，并使我们了解冰盖过程、全球营养循环和流入海洋的淡水通量。该项目将为研究生和博士后科学家提供跨学科培训，并通过桦树水族馆开发一个教育推广计划。冰川学中用于成像冰下水的标准地球物理测量技术(无线电回波测深和活动震源地震学)对水含量不直接敏感。相比之下，地面电磁(EM)方法通过其对整体电导率的影响而对水含量敏感。虽然EM方法在其他地质环境中的高精度水文学测绘中已经得到了很好的应用，但它们在冰盖上的应用还处于起步阶段。这项拟议的工作将使被动和主动源EM技术适用于冰川学问题，以量化冰流下和地面带冰川下水的三维结构。该项目将进行一系列合成反演研究，以确定EM技术在冰川学中的应用范围，并在惠兰斯冰原上进行实地实验，以根据先前的观测和模拟结果调查有关冰下水系统的两种假说：(1)冰下惠兰斯湖被一个深的咸水地下水库覆盖；(2)在接地线附近，可能在陆地上，存在冰下淡水与海水混合的河口区。

The Antarctic ice sheet is underlain by a dynamic water system that lubricates the flow of ice streams and outlet glaciers, provides a habitat for a diverse microbial ecosystem, and delivers freshwater and nutrients to the Southern Ocean. However, imaging this subglacial environment is difficult: Antarctica is a vast continent with ice up to four kilometers (2.5 miles) thick. To detect water at the ice-bed interface and in deeper groundwater reservoirs, this project will adapt a technique called electromagnetic sounding that is well-established on land and in the ocean for imaging fluids beneath the surface. Groundwater is estimated to be a significant part of the subglacial water budget in Antarctica, yet previous observational approaches have been unable to characterize its volume and distribution. This project will thus yield critical information about how ice-rock-water-ocean systems interact and inform our understanding of ice-sheet processes, global nutrient cycles, and freshwater flux to the ocean. The project will provide cross-disciplinary training for a graduate student and postdoctoral scientist, and develop an educational outreach program through the Birch Aquarium.Standard geophysical surveying techniques used in glaciology to image subglacial water (radio-echo sounding and active-source seismology) are not directly sensitive to water content. In contrast, ground-based electromagnetic (EM) methods are sensitive to water content through its impact on bulk conductivity. Although EM methods are well-established for high-precision mapping of hydrology in other geological environments, their application on ice sheets is in its infancy. The proposed work will adapt both passive- and active-source EM techniques to glaciological questions to quantify the three-dimensional structure of subglacial water beneath an ice stream and in a grounding zone. The project will perform a suite of synthetic inversion studies to determine the range of applications of EM techniques in glaciology and execute a field experiment on the Whillans Ice Plain to investigate two hypotheses about the subglacial water system based on previous observational and modeling results: (1) Subglacial Lake Whillans is underlain by a deep, saline groundwater reservoir; and (2) there is an estuary-like zone of mixing between fresh subglacial water and seawater near, and possibly landward, of the grounding line.