Distributed, Multi-Physical Fibre Optic Sensing of the Isunnguata Sermia Englacial Hydraulic System and its Impact on Glacial Dynamics

The transfer of surface meltwater to the base of the Greenland Ice Sheet modulates basal sliding, which controls ice loss into the ocean. The way in which water reaches the glacier bed, organizes itself near the ice-bed interface, and affects ice dynamics remains poorly understood due to limited observations. In this study, we present and interpret a multi-physical observational dataset from Isungnuata Sermia, West Greenland, acquired during the 2024 and 2025 melt seasons as part of the REASSESS and SLIDE projects.

We show how Distributed Fibre Optic Sensing (DFOS) measurements combined with meteorological observations and models, and Global Navigation Satellite System (GNSS) measurements of surface ice motion, provide observational constraints on and improve our conceptual understanding of the surface-to-bed hydrological connection. We deployed fibre optic cables at the surface and in four 600 m boreholes, providing measurements of temperature, strain, and seismicity at thousands of sensing points at the surface, and through the full depth of the glacier.

We observe that seismic activity is temporally linked with surface melt on a daily and weekly scale and evolves over time in alignment with the coalescence of surface channels. We apply Matched-Field Processing (MFP) beamforming to detect and locate seismic sources, aiming to resolve the vertical extent of fracturing related to water input. We observe the migration of some high-frequency seismic events to greater depths during periods of high runoff. This process is coincident with ice surface acceleration and subsequent deceleration events. Temperature and strain measurements from the DFOS system indicate highly variable distributions of temperature and deformation, which enable exploration of the prevalence and importance of englacial fracturing in surface-to-bed water transport.

Together, these data offer potential insights into the mechanism of fracture-driven water transport, basal pressure increase, and subsequent regulation and dissipation via subglacial-water-channel development, and the relationship of these processes to glacial dynamics.