Subglacial meltwater routes of the Fennoscandian Ice Sheet.

Subglacial drainage systems are crucial elements of glaciers and ice sheets because they modulate ice flow velocity. However, logistical challenges of measuring subglacial processes beneath contemporary ice and natural limitations in long-term monitoring hinder our understanding about their spatio-temporal evolution. Subglacial meltwater landforms created by palaeo-ice sheets are records of past subglacial drainage systems and offer the potential to study their large-scale development throughout deglaciation. Although collectively recording subglacial drainage, individual meltwater landforms such as eskers, meltwater channels and meltwater corridors, which comprise tunnel valleys and meltwater tracks (assemblages of landforms in broad, elongated paths with irregular surface texture), have mostly been investigated as separate entities. Using high-resolution (1-2 m) digital elevation models, we map integrated networks of subglacial meltwater landforms, herein called subglacial meltwater routes, on an ice-sheet scale in Fennoscandia. Our map provides a basis for future research on the long-term evolution of subglacial drainage networks and its effect on ice dynamics of the Fennoscandian Ice Sheet.

Rapid accelerations of Antarctic Peninsula outlet glaciers driven by surface melt.

Atmospheric warming is increasing surface melting across the Antarctic Peninsula, with unknown impacts upon glacier dynamics at the ice-bed interface. Using high-resolution satellite-derived ice velocity data, optical satellite imagery and regional climate modelling, we show that drainage of surface meltwater to the bed of outlet glaciers on the Antarctic Peninsula occurs and triggers rapid ice flow accelerations (up to 100% greater than the annual mean). This provides a mechanism for this sector of the Antarctic Ice Sheet to respond rapidly to atmospheric warming. We infer that delivery of water to the bed transiently increases basal water pressure, enhancing basal motion, but efficient evacuation subsequently reduces water pressure causing ice deceleration. Currently, melt events are sporadic, so efficient subglacial drainage cannot be maintained, resulting in multiple short-lived (<6 day) ice flow perturbations. Future increases in meltwater could induce a shift to a glacier dynamic regime characterised by seasonal-scale hydrologically-driven ice flow variations.

Discovery of relict subglacial lakes and their geometry and mechanism of drainage.

Recent proxy measurements reveal that subglacial lakes beneath modern ice sheets periodically store and release large volumes of water, providing an important but poorly understood influence on contemporary ice dynamics and mass balance. This is because direct observations of how lake drainage initiates and proceeds are lacking. Here we present physical evidence of the mechanism and geometry of lake drainage from the discovery of relict subglacial lakes formed during the last glaciation in Canada. These palaeo-subglacial lakes comprised shallow (<10 m) lenses of water perched behind ridges orientated transverse to ice flow. We show that lakes periodically drained through channels incised into bed substrate (canals). Canals sometimes trend into eskers that represent the depositional imprint of the last high-magnitude lake outburst. The subglacial lakes and channels are preserved on top of glacial lineations, indicating long-term re-organization of the subglacial drainage system and coupling to ice flow.