How do variations in ice-marginal lake water depth impact subglacial hydrology routing and ice dynamics?

Over 3,300 ice-marginal lakes exist around the Greenland Ice Sheet (GrIS), interacting with ~10% of its perimeter boundary. The number of ice-marginal lakes has increased over the last three decades, likely in response to enhanced meltwater runoff and glacier recession. We describe an ice-dammed, ice-marginal lake drainage event observed north of Isunnguata Sermia Glacier, south west Greenland in which ~1.6 million m³ of water drained from the 100 m deep lake over 4 days during the 2015 melt season. Using the Glacier Drainage System (GlaDS) model, fully-coupled to ice flow dynamics in the Ice-sheet and Sea-level System Model (ISSM), we model this ice-marginal lake drainage as an instantaneous drop in water level at the boundary of our model domain. By modifying the subglacial hydrological inflow/outflow boundary conditions, and tracking the evolution of the system through time in terms of channelised discharge, sheet thickness, effective pressure, and ice velocity we show that ice-marginal lake-drainage of the scale observed in 2015 causes significant reorganisation of the channelised subglacial drainage, both in the short term with a sudden injection of water and channel development, and in the long term with changes in the outlet boundary conditions and basal friction. As the number of ice-marginal lakes and the frequency of their drainage increases going forward we expect these dynamic drainage reorganisations to become more common, with implications for future GrIS dynamics.