Fresh groundwater far off the coast: 3D numerical simulations of groundwater flow at the New Jersey shelf

远离海岸的淡水地下水：新泽西陆架地下水流的 3D 数值模拟

基本信息

批准号：
279624715
负责人：
Professor Dr. Stefan Buske
金额：
--
依托单位：
Institut für Geophysik und Geoinformatik
依托单位国家：
德国
项目类别：
Infrastructure Priority Programmes
财政年份：
2015
资助国家：
德国
起止时间：
2014-12-31 至 2017-12-31
项目状态：
已结题

来源：
https://gepris.dfg.de/gepris/projekt/279624715?language=en
关键词：
Fresh groundwater far off coast

项目摘要

The aim of this study is to understand groundwater circulation at the New Jersey shelf (NJS) based on numerical simulations. In the late 1970, groundwater with salinities significantly lower than seawater was initially discovered in the course of the Atlantic Margin Coring Project along the eastern U.S. continental margin. Such fresh groundwater reserves were shown to be present within a distance of locally more than 100 km from the coastline. A particularly detailed record of pore water salinity was recovered in the course of IODP Leg 313 at the NJS, revealing abrupt vertical salinity variations at each of the three drilling locations. Previous studies either explained the existence of fresh groundwater at the NJS by present-day seaward directed meteoric groundwater flow or by fresh water emplacement during the last glacial period. However, which of these processes finally resulted in fresh groundwater at the NJS is currently debated. Also, the cause for the observed vertical salinity changes is little understood. In order to answer these questions, we will build a detailed 3D hydrogeological model for simulating groundwater flow at the NJS. On the basis of numerical simulations, the following working hypotheses to be tested are defined: 1. Fresh groundwater at the NJS was emplaced during the last glacial period. 2. Present-day submarine fresh groundwater discharge does not extend up to 100 km offshore. 3. The distribution of fresh submarine groundwater is controlled by low-permeability deposits. An excellent data base is available for building a 3D hydrogeological model. It consists of numerous 2D seismic profiles, 3D seismic data (by December 2015) as well as petrophysical and logging data, acquired during ODP Legs 150, 174A and IODP Leg 313. Depth-migration of seismic data will be performed for building a 3D hydrogeological model in depth. Definition of individual model sequences will be based on the published lithostratigraphic framework established after IODP Leg 313. Each sequence will be subdivided into geological facies, where each facies type is characterized by petrophysical properties obtained from ODP/IODP logs and laboratory measurements. By using a multiple-point geostatistical approach for modelling facies distribution, petrophysical properties derived from AVO analyses of 3D seismic data can also be incorporated into the model. Testing the working hypotheses defined above by numerical groundwater flow simulations requires careful definition of the initial and boundary conditions of the model, incorporating Pleistocene sea level and temperature variations, present-day fresh-water discharge at the coast, the hydraulic head (eventually accounting for ice sheet topography) and heat flux. Results of this study may be applicable to the entire eastern U.S. Atlantic margin where fresh water is widely encountered and will yield a better understanding of submarine groundwater discharge in general.

这项研究的目的是根据数值模拟了解新泽西州货架（NJS）的地下水循环。在1970年后期，在美国东部大陆边缘的大西洋边缘芯项目过程中，最初发现了盐度的地下水明显低于海水。这种新鲜的地下水储量显示出距离海岸线超过100公里的距离之内。在NJS的IODP腿313过程中回收了孔隙水盐度的特别详细记录，揭示了三个钻探位置中每个钻探的突然垂直盐度变化。先前的研究要么通过当今的海上导出的地下水流量来解释新泽西州在新泽西州的存在，要么通过在最后一个冰川时期通过淡水的淡水来解释。但是，目前在NJS上最终导致了新的地下水。而且，几乎没有理解观察到的垂直盐度变化的原因。为了回答这些问题，我们将建立一个详细的3D水文学模型，以模拟NJS的地下水流量。根据数值模拟，定义了要测试的以下工作假设：1。在最后一个冰川期间，NJS的新鲜地下水被安置。 2。当今的海底新鲜地下水排放量不会延伸到近海100公里。 3。新鲜海底地下水的分布由低渗透性沉积物控制。可用于构建3D水文学模型的出色数据库。它由许多2D地震曲线，3D地震数据（到2015年12月）以及岩石物理和记录数据，在ODP腿150、174A和IODP腿313期间获得。深度模型。单个模型序列的定义将基于IODP腿313后建立的已发表的岩石地层框架。每个序列将细分为地质相，在该相中，每种相类型的类型都由从ODP/IODP原木和实验室测量值获得的质量特性。通过使用多点的地统计方法进行建模相分布，也可以将来自3D地震数据的AVO分析得出的岩石物理特性纳入模型中。测试上面由数值地下水流量模拟定义的工作假设，需要仔细定义模型的初始和边界条件，并结合了更新世海平面和温度变化，当今海岸的淡水排放，液压头（最终核算冰盖地形）和热通量。这项研究的结果可能适用于整个美国东部的大西洋边缘，那里淡水广泛遇到，并且将更好地了解海底地下水排放。