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The Brunt Ice Shelf, Antarctica, accelerated rapidly from a velocity of 900 to 1500 m a -1 during 6 months, following calving of a 1500 km 2 iceberg on 22 January 2023. The immediate response to calving was observed as a change to the rate of acceleration and not to velocity directly. Acceleration increased by a factor of 10, with a second, smaller calving at the end of June 2023, leading to further tripling of acceleration. The acceleration was caused by the reduction of buttressing at the McDonald Ice Rumples, leading to high localised strain rates, which reduce the strength of the remaining ice shelf. [ABSTRACT FROM AUTHOR]

The Brunt Ice Shelf, Antarctica, accelerated rapidly from 900 m a-1 to 1500 m a-1 during six months following the calving of a 1500 km2 iceberg on 22nd January 2023. Initially, the rate of acceleration increased by a factor of ten, with a second, smaller calving at the end of June 2023 leading to further tripling of acceleration. The acceleration is caused by reduction of buttressing at the McDonald Ice Rumples due to loss of contact with the sea floor and has led to high strain rates to the south, with potential consequences for the stability of the remaining ice shelf. [ABSTRACT FROM AUTHOR]

Ice shelves influence the mass balance of the Antarctic Ice Sheet by restricting the flow of ice across the grounding zone. Their ability to restrict ice flow is sensitive to changes in their extent or thickness. Full thickness fractures, known as rifts, create tabular icebergs which reduce ice shelf extent. We present a method for measuring rift width using ICESat-2 laser altimetry, as part of a larger effort to detect, catalog and measure various characteristics of Antarctic rifts. We validate the results using optical satellite imagery and data from Global Navigation Satellite System (GNSS) receivers around "Halloween Crack" on Brunt Ice Shelf, East Antarctica. During the study period a further rift, "North Rift" formed and rapidly calved a ~1270 km2 iceberg. In response to this second rift, the opening of Halloween Crack approached stagnation before returning to opening at a reduced rate. We suggest the opening rate is controlled by the ice shelf geometry and degree of contact with a pinning point at McDonald Ice Rumples, and its influence on the large-scale ice flow field. We replicate the general pattern of opening using an inverse finite element model, and discuss the response of the ice shelf to the calving. We use historical satellite imagery and previously published ice-front positions to demonstrate the importance of McDonald Ice Rumples to the long-term calving and advance cycle of Brunt Ice Shelf. [ABSTRACT FROM AUTHOR]

Short-term tidal grounding line (GL) migration in Antarctica can impact ice dynamics at the ice sheet margins and obscures assessments of long-term GL advance or retreat. However, the magnitude of tidally-induced GL migration is poorly known, and the spatial pattern and modes of variability are not well characterised. Here we develop and apply a technique that uses ICESat-2 repeat-track laser altimetry to locate the inland limit of tidal ice shelf flexure for each sampled tide, enabling the magnitude and temporal variability of tidal GL migration to be resolved. We demonstrate its application at an ice plain north of Bungenstockrücken, in a region of the southern Ronne Ice Shelf subject to large ocean tides. We observe a 1,300 km² area of ephemeral grounding over which the GL migrates by up to 15 km between low and high tide, and identify four distinct modes of migration: “linear”, “asymmetric”, “threshold” and “hysteresis”. The short-term movement of the GL dominates any long-term migration signal in this location, and the distribution of GL positions and modes contains information about spatial variability in the ice-bed interface. We discuss the impact of extreme tidal GL migration on ice shelf-ocean-subglacial systems in Antarctica and make recommendations for how GLs should be more precisely defined and documented in future by the community. [ABSTRACT FROM AUTHOR]

Fox Glacier/Te Moeka o Tuawe is a fast-responding maritime glacier that has undergone multiple advance and retreat phases during recent decades. Here we use a combination of repeat photography, Structure from Motion (SfM), and ice discharge measurement, to identify key morphological differences associated with these repeated phase changes, and assess how much of the current terminus is still dynamically active. Increasing surface-debris cover at the margins and topographic shading result in the asymmetry of the retreating terminus, with central portions receding faster than the margins. In 2019, the glacier is shorter than at any time in recorded history, and ice flux is insufficient to sustain the current glacier length, with a further ∼300 m of the glacier terminus region potentially vulnerable to retreat. However, due to the high climate sensitivity of this maritime glacier, even a slight shift towards increasing mass flux could see this trend reverse. [ABSTRACT FROM AUTHOR]

We present a diagnostic glacier flowline model parameterized and constrained by new velocity data from ice-surface GPS installations and speckle tracking of TerraSAR-X satellite images, newly acquired airborne-radar data, and continental gridded datasets of topography and geothermal heat flux, in order to better understand two outlet glaciers of the East Antarctic ice sheet. Our observational data are employed as primary inputs to a modelling procedure that first calculates the basal thermal regime of each glacier, then iterates the basal sliding coefficient and deformation rate parameter until the fit of simulated to observed surface velocities is optimized. We find that the two glaciers have both frozen and thawed areas at their beds, facilitating partial sliding. Glacier flow arises from a balance between sliding and deformation that fluctuates along the length of each glacier, with the amount of sliding typically varying by up to two orders of magnitude but with deformation rates far more constant. Beardmore Glacier is warmer and faster-flowing than Skelton Glacier, but an up-glacier deepening bed at the grounding line, coupled with ice thicknesses close to flotation, lead us to infer a greater vulnerability of Skelton Glacier to grounding-line recession if affected by ocean-forced thinning and concomitant acceleration. [ABSTRACT FROM AUTHOR]