The Antarctic ice sheet has been losing mass over the past decades through the accelerated flow of its glaciers conditioned by ocean temperature and bed topography. Glaciers retreating along retrograde slopes (i.e., bed elevation drops in the inland direction) are potentially unstable, whereas subglacial ridges slow down the glacial retreat. Despite major advances in mapping subglacial bed topography, significant sectors of Antarctica remain poorly resolved and critical spatial details are missing. Here we present a novel, high-resolution, and physically-based description of Antarctic bed topography using mass conservation. Our results reveal previously unknown basal features with major implications for glacier response

Here we present new measurements of an anisotropic ice fabric in a fast moving (377 ma−1) ice stream in West Antarctica. We use ∼6000 measurements of shear wave splitting observed in microseismic signals from the bed of Rutford Ice Stream, to show that in contrast to large‐scale ice flow models, which assume that ice is isotropic, the ice in Rutford Ice Stream is dominated by a previously unobserved type of partial girdle fabric. This fabric has a strong directional contrast in mechanical properties, shearing 9.1 times more easily along the ice flow direction than across flow. This observed fabric is likely to be widespread and representative of fabrics in other ice streams and large glaciers, suggesting it is essential to consider anisotropy in data‐driven models to correctly predict ice loss and future flow in these regions. We show how passive microseismic monitoring can be effectively used to provide these data.

Flow dynamics of the ice streams that drain the Antarctic Ice Sheet are heavily influenced by processes at the bed. Natural seismic activity generated beneath an ice stream is associated with the motion of the ice over its bed and can be used to map both the characteristics of the ice-bed interface and to understand these basal processes. Basal microseismicity was recorded over a 34 day period on Rutford Ice Stream, West Antarctica, using 10 three-component geophones 40 km upstream of the grounding line. Around 3000 microseismic events were located in discrete spatial clusters near the ice-bed interface. The activity of each cluster varies with time, and the source mechanism for the events is interpreted as subhorizontal, low-angle faulting, slipping in the ice flow direction. Cluster locations are interpreted as "sticky spots" of stiff basal sediment at the ice-bed interface, where ice movement is accommodated by stick-slip basal sliding. The sticky spots occur in areas where independent active-source seismic surveys show low porosity sediments at the bed. We show that the sticky spots probably accommodate only a small amount of the total basal motion. Our results suggest that most of the ice stream basal motion is accommodated by aseismic deformation of soft, dilatant basal sediment, or by a well-lubricated, stiffer bed.