Few subglacial lakes have been identified beneath the Greenland Ice Sheet (GrIS) despite extensive documentation in Antarctica, where periodic release of water can impact ice flow. Here we present an ice-sheet-wide survey of Greenland subglacial lakes, identifying 54 candidates from airborne radio-echo sounding, and 2 lakes from ice-surface elevation changes. These range from 0.2–5.9 km in length, and are mostly distributed away from ice divides, beneath relatively slow-moving ice. Based on our results and previous observations, we suggest three zones of formation: stable lakes in northern and eastern regions above the Equilibrium Line Altitude (ELA) but away from the interior; hydrologically-active lakes near the ELA recharged by surface meltwater and; small, seasonally-active lakes below the ELA, which form over winter and drain during the melt season. These observations provide important constraints on the GrIS's basal thermal regime and help refine our understanding of the subglacial hydrological system.

Subglacial lakes store ancient climate records, provide habitats for life, and modulate ice flow, basal hydrology, biogeochemical fluxes and geomorphic activity. In this Review, we construct the first global inventory of 773 subglacial lakes, including 675 from Antarctica (59 newly identified in this study), 64 from Greenland, 2 beneath Devon Ice Cap, 6 beneath Iceland's ice caps, and 26 from valley glaciers. The inventory is used to evaluate subglacial lake environments, dynamics, and their wider impact on ice flow and sediment transport. We suggest their behaviour is conditioned by the subglacial setting and the hydrologic, dynamic and mass balance regime of the ice mass above. Using space-time substitution, we predict fewer and smaller lakes but increased activity with higher discharge drainages of shorter duration where climate warming causes ice-surface steepening. Coupling to surface melt and rainfall inputs will modulate fill-drain cycles and seasonally enhance oxic processes. Higher discharges cause large, transient ice-flow accelerations, but might result in overall net slowdown due to development of efficient subglacial drainage. Future subglacial lake research requires new drilling technologies, and the integration of geophysics, satellite monitoring and numerical modelling, which will provide new insight into their wider role in a changing Earth system.

Abstract. We report three active subglacial lakes within 2 km of the lateral margin of Isunguata Sermia, West Greenland, identified by differencing time-stamped ArcticDEM strips. Each lake underwent one drainage–refill event between 2009 and 2017, with two lakes draining in < 1 month in August 2014 and August 2015. The 2015 drainage caused a ∼ 1-month down-glacier slowdown in ice flow and flooded the foreland, aggrading the proglacial channel by 8 m. The proglacial flooding confirms the ice-surface elevation anomalies as subglacial water bodies and demonstrates how their drainage can significantly modify proglacial environments. These subglacial lakes offer accessible targets for geophysical investigations and exploration.