Continental-scale observations of seawater infiltration in Antarctic ice shelves reveal an overlooked hydrologic system

Dynamic hydrologic networks on and within ice shelves are increasingly recognized as critical controls on ice shelf stability and ice sheet mass loss. To date, ice shelf hydrology has been primarily framed in terms of surface-derived meltwater, including supraglacial pond formation, firn infiltration and refreezing, and meltwater aquifer development. Recent firn modeling suggests that a substantial fraction of Antarctic ice shelf firn lies below sea level, providing extensive pore space that is susceptible to seawater intrusion and brine aquifer formation. Despite this potential, seawater infiltration into porous firn has remained largely unexplored beyond a small number of spatially limited observations, many of which were collected decades ago.

Here, we present the first continental-scale observational assessment of seawater-derived aquifers within Antarctic ice shelves. We analyzed ~145,000 km of airborne radar flightlines and identified diagnostic brine signatures along ~4,500 km of profiles spanning more than 30 Antarctic ice shelves, demonstrating that seawater infiltration occurs wherever suitable observations exist. By reconciling radargrams with available digital elevation models and lidar data, we show that the dominant infiltration mechanisms vary regionally: Antarctic Peninsula ice shelves commonly exhibit large infiltration zones in thin or damaged ice, whereas East Antarctic ice shelves are characterized by localized intrusion along rifts and basal crevasses. We further map the depth of the brine water table across these systems, revealing spatial variability in aquifer geometry linked to ice shelf structure and infiltration mechanism. Climate model projections indicate that regions currently hosting brine aquifers are projected to experience larger future increases in surface meltwater inputs than ice shelf regions without detected brine, highlighting the potential for the development of mixed aquifer systems. Our results demonstrate that seawater infiltration represents a widespread and previously underappreciated hydrologic pathway within Antarctic ice shelves and highlight the need to incorporate these systems into emerging frameworks of ice shelf hydrology and stability.