During the first three years we will develop integrated methodologies and technologies to investigate aquifers offshore Malta. Malta is representative for a large part of the Mediterranean coast line, and is also one of the ten poorest countries globally in terms of water resources per inhabitant. The archipelago hosts an excellent example of unconfined carbonate rock aquifer onshore which is overlain by an aquitard. This aquitard continues offshore out to the shelf break. Existing borehole data and pockmarks indicate that the groundwater aquifer extends offshore, but so far it is unknown if the underlying aquifer also extends all the way to the shelf break or if it terminates somewhere on the shelf. Finding this out is one of the objectives of the project. Groundwater is known to seep along the coastline and shallow seafloor. Electromagnetic and ROV data are presently being collected by team members in the framework of MARCAN, a 5-year project funded through a European Research Council (ERC) Starting Grant that focuses on the role of offshore groundwater seepage in sea geomorphology.
The planned work for SMART is divided into three work packages:
SMART is planned over 3 years and divided into 3 Work Packages (WP), which are directly linked to the objectives and lead into a set of deliverables (D). Within SMART we want to detect and quantify OAs across the coastal zone. In a first step, we will compile all relevant existing information on the work area (WP1a). The detection will be based on a combination of onshore/offshore electromagnetic and seismic measurements (WP1b). Electromagnetic data react very sensitively to pore water salinity, as it changes the bulk conductivity of the seafloor. However, changes in bulk resistivity may also be caused by lithological variations. Seismic data, on the other hand, are largely unaffected by the salinity of pore fluids yet are very sensitive to lithological variations and can resolve the geometry of aquifers at high resolution. To achieve a high-resolution Earth model of aquifers we will integrate the electromagnetic data with seismic data and ground-truthing from boreholes. Most efficient and reliable results are obtained if the data are jointly inverted to a common Earth model (WP1e). The data integration and joint inversion requires knowledge of the relationship between different physical parameters such as electrical conductivity, seismic velocity, grain-size and porosity, which may be obtained at borehole calibration points (WP1c). Information from WP1a to WP1e will be combined to construct an Earth model with hydrologically relevant parameters (WP1e).
Based on this model, we will propose suitable pore-water sampling locations for geochemical analysis in order to constrain the age of the groundwater, residence time, and recharge rates. Postulated offshore freshwater seepage sites, constrained by WP1, will be ground-truthed and sampled for geochemical measurements (WP2). The ground-truthing strategy includes well-established hydroacoustic and oceanographic exploration tools developed for cold seep studies (WP2a). Offshore water-/porewater sampling and chemical analyses of seeping fluids from the seafloor will be conducted in WP2b. The geochemical characteristics of seeping fluids will help to indicate different origin of water and secondary water/sediment interaction by end-member calculations. Palaeowaters and young meteoric waters will be indicated by radio-isotope measurements.
Together with long-term seepage monitoring (WP2c), results from WP1 and WP2 be used to inform 2D and 3D hydrogeologic models (WP3a-d) that will enhance our understanding of how OAs will respond to natural and human-induced forcing mechanisms.
Study area offshore Malta. Within the dashed black box there are single-channel 2D seismic lines, and complete multi-beam echosounder coverage. The CSEM lines (yellow) were acquired in October, 2018. The red box and the red lines are approximate locations for the data that will be acquired in year 2 of SMART. The precise location and survey configuration as well as the geochemical sampling programme will depend on the results of the first year of SMART.
Detection, characterization and quantification of offshore aquifers
Lead: Marion Jegen/GEOMAR
Modified from Schwalenberg et al. (2017)
Nature and age of offshore aquifers
Lead: Mark Schmidt/GEOMAR
Photos: Mark Schmidt/GEOMAR
Evolution of offshore aquifers
Lead: Aaron Micallef/University of Malta
Cohen et al. (in press)