OFFING project

Offshore freshened groundwater (OFG) refers to water stored in porous sediments and fractured rocks beneath the seafloor, with a salinity lower than that of seawater. It has been estimated that the global volume of OFG is in the order of 10⁵ ~ 10⁶ km³, which is about one-tenth the global volume of shallow groundwater. These order-of-magnitude calculations suggest that OFG may be a potential fresh water source in the future. OFG systems are also of interest because an enhanced understanding of their key control mechanisms could advance the knowledge of fluid migration processes and biogeochemical fluxes to the ocean, which, in turn, has direct implications for benthic and sub-seafloor ecology, and more generally on the course of environmental change. However, our current knowledge of the functioning of OFG systems is still very limited, which is due to a lack of available data that would allow for an unambiguous interpretation of OFG emplacement. 

The DFG funded project “OFFshore freshened groundwater systems – Emergence and persistence analysis by geochemical modellING (OFFING)” will take a comprehensive approach to leveraging available biogeochemical data to constrain the timing and emplacement mechanisms of two typical OFG systems: the New Jersey shelf and Canterbury Bight. This will involve a thorough quantitative evaluation of high-resolution pore water biogeochemical data (from IODP 313 and 317) using 1D and 2D numerical transport-reaction models. In addition to identifying the processes behind observed porewater biogeochemical distribution patterns, the models will quantify and constrain fluxes, reaction rates, and flow velocities. As a consequence, the question of whether an OFG system is actively recharging or not (i.e., fossil groundwater) will be answered, which has important implications for their potential use as a source of potable water.