A geological and geophysical database for the assessment of offshore freshened groundwater resources

Fresh groundwater resources in coastal regions are vital for modern society, but are under considerable pressure due to population growth, seasonal peaks in demand, pollution and climate change. In recent years, interest in offshore freshened groundwater (OFG) has surged, as potential resource for addressing these challenges. Recent studies have documented OFG occurrences on many continental margins and islands, with global volume estimates ranging between 105-10⁶ km3. However, these global estimates rely on simplified assumptions regarding aquifer geometry and properties, as they only are intended to give an idea of the scale of these resources. Focused studies on specific coastal regions are required to evaluate the distribution of these resources locally. However, these studies are often hampered by the technical challenge and high cost of acquiring and processing data in marine regions. Thus, the understanding of aquifers, including their occurrence, volumes, and their geological and hydrological properties, remains limited. In this context, this study aims to develop a comprehensive, open access database that integrates existing geophysical, geological, and geochemical datasets to enhance OFG characterisation and modelling capabilities in the Euro-Mediterranean region. Moreover, this database aims to support hydrological studies on offshore aquifers and coastal hydrology, and help modelling of groundwater flow from recharge areas. The remaining challenges regarding data accessibility and resolution are then discussed, underscoring the need for further interdisciplinary research and data sharing to ensure the sustainable management of this valuable resource.