10 March 2017

Leaky plumbing impedes Greenland Ice Sheet flow

Water draining from weakly connected underlying regions limits ice flow in late summer and beyond


Surface meltwater that drains to the bed of the Greenland Ice Sheet each summer causes changes in ice flow that cannot be fully explained by prevailing theories.  Application of a new model for extensive, sediment-choked subglacial “swamps” at the ice sheet bed found that slow leakage of water from those areas explains why the ice sheet’s movement slows down in late summer and winter. 


The new model extends the long-recognized complexity of terrestrial hydrology to the historically simplified understanding of hydrology beneath glaciers, adding a third component to the longstanding traditional conceptual model of subglacial hydrology.


To assess if changes in weakly connected, swampy areas of the bed that have been previously ignored can explain why the ice sheet slows down in late summer and winter, the researchers developed a new model for weakly connected subglacial drainage and coupled it to an existing subglacial drainage model that includes distributed and channelized flow.  When applied to a well-studied field site in Greenland by forcing the enhanced model with measurements of meltwater input to the ice sheet, the model matches water pressure variations previously measured in different parts of the subglacial drainage system.  Additionally, modeled ice speed shows the same seasonal pattern as the observations – the same water levels in the moulin that drains water to the bed result in slower ice speed later in the summer.  This is because the weakly connected regions of the bed become better connected as the basal drainage system grows during summer, causing some of these high-pressure areas to leak stored water.  Lower water pressure and less lubrication of the bed lead to slower ice motion. 

Matthew Hoffman
Los Alamos National Laboratory
Hoffman, M., Andrews, L., Price, S., Catania, G. & et al. "Greenland subglacial drainage evolution regulated by weakly connected regions of the bed." Nature Communications 7, 13903 (2016). [10.1038/ncomms13903].