Collaborative Research: A Pilot Study for Electromagnetic Surveying of Freshwater Resources Beneath the US Atlantic Continental Shelf

合作研究：美国大西洋大陆架淡水资源电磁测量试点研究

• 批准号: 1458392
• 负责人: Kerry Key
• 金额: $ 24万
• 依托单位: University of California-San Diego Scripps Inst of Oceanography
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-04-01 至 2017-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1458392&HistoricalAwards=false
• 关键词: Collaborative; Research; Pilot; Study; Electromagnetic

Supplies of fresh drinking water typically come from aquifers deep below the surface. These aquifer units do not stop at the shoreline, but instead extend offshore for perhaps hundreds of kilometers, carrying freshwater with them. In some cases, it is suspected that isolated bodies of freshwater may exist, emplaced during periods of time when sea level was much lower than it is today. Although the presence of large volumes of freshwater beneath the continental shelf is likely a global phenomenon, estimates of the extent of potential resources vary widely. A recent modeling study suggests that as much as 1300 km3 of fresh water could be trapped off the New England shore. For reference, the city of New York consumes roughly 1.5 km3 per year. As freshwater resources become increasingly stressed, many nations will need to exploit these valuable resources in a manner that does not result in contamination of the freshwater supply. Although we suspect that extensive freshwater exists offshore, our knowledge of where the water can be found is limited to drilling sites where samples have been collected. For example, it has been known for ~40 years that a substantial body of freshwater can be found offshore New Jersey. However, drilling gives only point measurements and is prohibitively expensive when large areas need to be studied. What is missing are tools capable of mapping the subsurface that are sensitive to fresh groundwater and for mapping deposits in new areas where water supplies onshore are scarce. This research takes advantage of electromagnetic surveying tools that were initially developed by academia, but which have been adopted and expanded by the petroleum industry. These tools measure how well the seafloor can conduct electrical current and, as a result, are sensitive to changes in the salinity of water in the subsurface because fresh water conducts current less than seawater. The electromagnetic methods that will be used in this projet are the only non-invasive means available to detect the presence of fresh-water in the subsurface and to map these layers over length-scales of tens of kilometers. In this research, the project will characterize the spatial distribution of sub-seafloor fresh water beneath the continental shelf of the US Atlantic coast in two locations: off Martha's Vineyard, Massachusetts, and the offshore New Jersey. Broader impacts of the work include providing a proof of concept that electromagnetics can be effectively used to detect freshwater reserves in the offshore marine environment.

新鲜饮用水的供应通常来自地表深处的含水层。这些含水层单位并不停留在海岸线，而是向近海延伸大约数百公里，并携带着淡水。在某些情况下，人们怀疑可能存在孤立的淡水体，这些淡水体是在海平面远低于现在的时期形成的。 尽管大陆架下存在大量淡水可能是一种全球现象，但对潜在资源范围的估计差异很大。最近的一项模型研究表明，新英格兰海岸可能滞留多达 1300 平方公里的淡水。作为参考，纽约市每年消耗约 1.5 平方公里。随着淡水资源的压力越来越大，许多国家需要以不会导致淡水供应污染的方式开发这些宝贵的资源。尽管我们怀疑近海存在大量淡水，但我们对在哪里可以找到水的了解仅限于收集样本的钻井地点。例如，大约 40 年前人们就知道新泽西州近海有大量淡水。然而，钻孔只能提供点测量，并且当需要研究大面积时，其成本过高。目前缺少的是能够绘制对淡水敏感的地下区域的工具，以及能够绘制陆上供水稀缺的新地区沉积物的工具。这项研究利用了电磁测量工具，这些工具最初由学术界开发，但已被石油工业采用和扩展。这些工具测量海底传导电流的能力，因此对地下水的盐度变化很敏感，因为淡水传导电流的能力小于海水。该项目将使用的电磁方法是唯一可用于检测地下淡水存在并绘制数十公里长度范围内这些层的非侵入性方法。在这项研究中，该项目将描述美国大西洋海岸大陆架下两个地点海底淡水的空间分布：马萨诸塞州玛莎葡萄园岛附近和新泽西州近海。这项工作的更广泛影响包括提供电磁学可有效用于检测近海海洋环境中淡水储量的概念证明。