Methods

Cutler et al. (2000) used a time-dependent, two-dimensional, thermomechanically coupled finite-element flowline model. The model domain extends 1000 m into the subsurface to accommodate permafrost dynamics and groundwater flow.

Permafrost growth and decay is modelled by solving the heat flow equation for mixtures of parent material, water, and ice and accounting for latent heat from phase changes. Subglacial groundwater flow, fed by basal melting, is calculated from the Darcy equation. At a given node, the available vertical extent of permeable substrate—if any—for meltwater drainage varies through time as permafrost evolves. The model tracks the volume of subglacially stored water.

Ice-sheet evolution, driven by changes in mass balance, is forced by air temperature and precipitation at the ice surface between 55 and 21 kyr before present. Their temporal variation was estimated from palaeoclimate records. Because heat flow is modelled in the bed as well as the ice lobe, air temperature fluctuations also drive permafrost dynamics. The impacts of geo-thermal heat and potential energy released from groundwater are also modelled.

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