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

• Applicant: Professor Dr. Christoph Clauser, since 5/2019
• Subject Area: Palaeontology ; Geophysics
• Term: from 2016 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 319552648

The aim of this study is to understand groundwater circulation at the New Jersey shelf (NJS). In the late 1970’s, groundwater with salinities significantly lower than seawater was discovered 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. In order to understand which of these processes finally resulted in fresh groundwater emplacement, we aim to simulate groundwater flow at the NJS, based on a detailed 3D hydrogeological model. 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. In addition to petrophysical and logging data acquired during previous ODP/IODP expeditions, these data consist of numerous 2D seismic lines. The same-named proposal received DFG funding at TU Freiberg in 2015 and at RWTH Aachen in 2016. Depth-migration of seismic reflection data is close to completion and serves as a basis for building a hydrogeological model. We built a complex and geologically plausible 2D facies model based on geostatistical methods. This model comprises more than 30 Million cells and honors seismic picks of sequence boundaries and log-derived grain size distribution trends. Each facies type is parametrized by petrophysical properties, derived from well logs, core data and from a literature review. After careful definition of initial and boundary conditions, first simulations were run, showing promising results that tentatively confirm the hypotheses stated above. Future work includes extension of the hydrogeological model into 3D and testing of alternative facies modelling approaches such as multiple-point geostatistics. Petrophysical properties derived from AVO analyses of seismic data shall also be incorporated into the model by serving as a guide for stochastic facies distribution. Finally, numerical simulations will be performed on the basis of the final 3D hydrogeological model for testing the hypotheses stated above. Results of this study will yield a better understanding of submarine groundwater discharge in general.

• DFG Programme: Infrastructure Priority Programmes
• Subproject of: SPP 527: Bereich Infrastruktur - "International Ocean Discovery Program" (IODP)
• Ehemaliger Antragsteller: Dr. Sönke Reiche, until 4/2019