High-resolution modelling of the seasonal evolution of surface water storage on the Greenland Ice Sheet

• Main Authors: Arnold, NS, Banwell, A, Willis, IC
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2014
• Subjects: 3707 Hydrology; 3709 Physical Geography and Environmental Geoscience; 37 Earth Sciences; 3705 Geology; Greenland; Rapid Lake; Ice Sheet
• Online Access: https://www.repository.cam.ac.uk/handle/1810/273621; https://doi.org/10.17863/CAM.20690

Seasonal meltwater lakes on the Greenland Ice Sheet form when surface runoff is temporarily trapped in surface topographic depressions. The development of such lakes affects both the surface energy balance and dynamics of the ice sheet. Although areal extents, depths, and lifespans of lakes can be inferred from satellite imagery, such observational studies have a limited temporal resolution. Here, we adopt a modelling-based strategy to estimate the seasonal evolution of surface water storage for the ~3600 km2 Paakitsoq region of W. Greenland. We use a high-resolution time dependent surface mass balance model to calculate surface melt, a supraglacial water routing model to calculate lake filling and a prescribed water-volume based threshold to predict rapid lake drainage events. This threshold assumes that drainage will occur through a fracture if V = Fa.H, where V is lake volume, H is the local ice thickness and Fa is the potential fracture area. The model shows good agreement between modelled lake locations and volumes and those observed in 9 Landsat 7 ETM+ images from 2001, 2002 and 2005. We use the model to investigate the lake water volume required to trigger drainage, and the impact that varying this threshold volume has on the proportion of meltwater that is stored in surface lakes and enters the subglacial drainage system. Model performance is maximised with values of Fa between 4000 and 7500 m2. For these thresholds, lakes transiently store <40% of available meltwater at the beginning of the melt season, decreasing to ~5 to 10% by the middle of the melt season; over the course of a melt-season, 40 to 50% of total meltwater production enters the subglacial drainage system through moulins at the bottom of drained lakes. This work was partially funded by the UK Natural Environment Research Council Doctoral Training grant to A. F. Banwell (LCAG/ 133) (CASE Studentship with The Geological Survey of Denmark and Greenland (GEUS)).