Active hydrogen emissions offshore the Maltese Islands: implications for an aborted Mesozoic rift in the Sicily Channel

The growing interest in natural hydrogen as a low-carbon energy carrier calls for a better understanding of its geological sources and migration pathways, particularly in marine rifted margins. In this study, we document active seepage from pockmarks offshore the Maltese Islands, providing the first evidence of hydrogen-rich emission in the Mediterranean Sea and offering new constraints on the geodynamic controls governing natural H₂ circulation. Integrated multibeam bathymetry, sub-bottom profiler, and multichannel seismic data reveal more than 1,000 pockmarks preferentially aligned along NW-SE trending escarpments. These structures appear to be inherited transtensional faults from a Mesozoic Sicily Channel Rift, a rifting system that ultimately aborted prior to full continental break-up. Although no longer seismically active, these faults remain mechanically open and permeable, acting as long-lived fluid conduits that promote upward gas migration. Geochemical analyses of water-column samples collected within active pockmarks show anomalously high dissolved H₂concentrations, associated with elevated helium values and systematic relationships with uranium, thorium, and light rare earth elements. These signatures indicate a predominantly crustal hydrogen source, most plausibly generated by radiolytic water splitting and water-rock interactions within the continental crust. We propose that hydrogen release in the study area is controlled by a leakage-dominated system, where structural inheritance from an aborted rift governs present-day fluid circulation in the absence of active tectonic deformation. This study highlights the critical role of fossil rift architectures as persistent pathways for deep-sourced gases and underscores the importance of considering aborted rift systems as prime targets for natural hydrogen exploration and for understanding long-term fluid flow in rifted continental margins.