Subglacial environments are among the least accessible regions on Earth and represent one of the last physical frontiers of glaciological research, while emerging as a unique ecological habitat. The subglacial environment is a key component in the dynamic behaviour of ice sheets and glaciers, involving complex and precise mass and energy transfers between the ice and its substrate of water, air, bedrock, or sediment, and the oceans at ice sheet boundaries. In particular, determining the distribution and nature of water flows at the ice-mass bed is highlighted as a priority for understanding and predicting ice dynamics. For example, both remote sensing and ground-based observations across Antarctica and Greenland highlight the existence of subglacial water in a variety of forms, ranging from vast subglacial lakes (providing distinctive habitats for potentially unique life forms) to mm-thick water flows at the ice-substrate interface. Feedbacks between increased surface melting, glacier bed conditions and ice flow also affect alpine glaciers, potentially contributing to increased glacial retreat in low and mid-latitude mountain regions.

It is clear that subglacial processes impact ice dynamics, transcending ice-mass scales from valley glaciers to large ice sheets and, through feedback loops, contribute to changes in sea level, ocean circulation, and climate evolution. Quantitative characterisation of the basal environment therefore remains an outstanding glaciological problem, as does scaling of this knowledge for use in modelling ice sheet and glacier behaviour.

We invite scientific contributions that include, but are not limited to, measurements and/or modelling of: (i) flow of subglacial water at the bed and through subglacial sediments; (ii) linkages between subglacial hydrology and ice dynamics; (iii) theoretical-, field-, or laboratory-based parameterisation of subglacial processes in numerical ice-flow models; (v) formation, geometry and potential hydrological linkages between subglacial lakes; (v) subglacial and supraglacial lake drainage and subglacial floods from ice margins; and (vi) geomorphological evidence of subglacial water flows from contemporary ice-sheet margins and across formerly glaciated continental-scale regions.