In Part 1, we have considered the dynamics of topographically confined glaciers, which may undergo surge cycles when the bed becomes temperate. In this Part 2, we consider the ice discharge over a flatbed, which would self-organize into alternating stream/ridge pairs of wet/frozen beds. The meltwater drainage, no longer curbed by the bed trough, would counter the conductive cooling to render a minimum bed strength at some intermediate width, toward which the stream would evolve over centennial timescale. At this stationary state, the stream width is roughly twice the geometric mean of the stream height and length, which is commensurate with its observed width. Over a flatbed, streams invariably interact, and we deduce that the neighboring ones would exhibit compensating cycles of maximum velocity and stagnation over the centennial timescale. This deduction is consistent with observed time variation of Ross ice streams B and C (ISB/C), which is thus a manifestation of the natural cycle. Moreover, the model uncovers an overlooked mechanism of the ISC stagnation: as ISB widens following its reactivation, it narrows ISC to augment the loss of the meltwater, leading to its stagnation. This stagnation is preceded by ice thickening hence opposite to the thinning-induced surge termination.

Geothermal heat flux (GHF) is one of the key thermal boundary conditions for ice-sheet models. We assess the sensitivity of the Lambert-Amery glacial system in East Antarctica to four different GHF datasets using a regional ice-sheet model. A control solution of the regional model is initialised by minimising the misfit to observations through an optimisation process. The Lambert-Amery glacial system simulation contains temperate ice up to 150 m thick and has an average basal melt of 1.3 mm a−1, with maximum basal melting of 504 mm a−1. The simulations which use a relatively high GHF compared to the control solution increase the volume and area of temperate ice, which causes higher surface velocities at higher elevations, which leads to the advance of the grounding line. The grounding line advance leads to changes in the local flow configuration, which dominates the changes within the glacial system. To investigate the difference in spatial patterns within the geothermal datasets, they were scaled to have the same median value. These scaled GHF simulations showed that the ice flow was most sensitive to the spatial variation in the underlying GHF near the ice divides and on the edges of the ice streams.

Lakes beneath the Antarctic Ice Sheet are known to decrease traction at the ice base and therefore can have a great impact on ice dynamics. However, the total extent of Antarctic subglacial lakes is still unknown. We address this issue by combining modeling and remote-sensing strategies to predict potential lake locations using the general hydraulic potential equation. We are able to reproduce the majority of known lakes, as well as predict the existence of many new and so far undetected potential lakes. To validate our predictions, we analyzed ice-penetrating radar profiles from radio-echo sounding flights acquired over 1994–2013 in Dronning Maud Land, East Antarctica, and this led to the identification of 31 new subglacial lakes. Based on these findings, we estimate the total number of Antarctic subglacial lakes to be ~1300, a factor of three higher than the total number of lakes discovered to date. We estimate that only ~30% of all Antarctic subglacial lakes and ~65% of the total estimated lake-covered area have been discovered, and that lakes account for 0.6% of the Antarctic ice/bed interface.

Marine-terminating outlet glaciers discharge most of the Greenland ice sheet's mass through frontal ablation and meltwater runoff. While calving can be estimated by in situ and remote sensing observations, submarine melting and subglacial meltwater transport are more challenging to quantify. Here we investigate the subglacial hydrology of Rink Isbræ, a fast-flowing West Greenland tidewater glacier, using time-lapse photography, modeled runoff estimates and daily satellite imagery from 2007 to 2011. We find that sediment plumes appear episodically at four distinct locations across the terminus, and last between 2 h and 17 d. This suggests short-term variability in discharge and the existence of persistent pathways. The seasonal onset of sediment plumes occurs before supraglacial lake drainages, shortly after the onset of runoff, and only after the wintertime ice mélange has begun disintegrating. Plumes were also visible after the cessation of runoff (23 ± 5 d), which is indicative of subglacial storage. The lack of either a seasonal velocity change or a correspondence between meltwater availability and plume occurrence suggests that the subglacial system persists in a state of inefficient drainage. Subglacial hydrology at tidewater glaciers is of critical importance in understanding dynamics at the ice front.