Dynamic small-scale morphology and mass-loss processes near the fronts of Antarctica's large ice shelves

Close to half of the melting below each of Antarctica's two largest ice shelves, Ross (RIS) and Filchner-Ronne (FRIS), occurs within 100 km of their ice fronts and is related to the intrusion of warm upper-ocean waters beneath the front. This results in a broad region where the surface elevation declines fairly smoothly toward the ice front. In some areas, erosion of the ice front near its waterline leaves behind a submerged bench of ice whose buoyancy pushes the seaward edge upward and causes a depression typically within a kilometer of the subaerial ice front. Eventually, this stress imbalance leads to an edge-wasting calving event. Here, we investigate the distribution and evolution of this "rampart-moat" morphology with airborne and satellite laser altimetry across the RIS front. Airborne laser altimetry data from the interdisciplinary ROSETTA-Ice project provide swath profiles of elevation at 20 locations along the RIS front for the austral summers of 2015-2017, and repeat-track laser altimetry data from the Ice, Cloud and land Elevation Satellite (ICESat) provide multiple repeats along 145 tracks that sampled the front between 2003 and 2009. The ROSETTA-Ice and ICESat observations both point to the prevalence of the rampart-moat feature on RIS, while the ICESat data also enable us to examine the evolution of small-scale ice-front morphology through time and for other ice shelves including FRIS and Amery. Several tracks that cross the RIS front show a cycle of calving and subsequent rampart-moat redevelopment. We discuss observed spatial patterns in ice-front evolution and geometry in the context of the regional oceanography and sea-ice variability that influence seasonal warming of the upper ocean near the ice front. Combining these observations with insights from elastic and viscous ice-shelf models, we estimate the amount of mass loss by small-scale calving associated with rampart-moat formation and its contribution to ice-shelf-wide calving flux, and speculate about how this mass-loss term might increase in future climates. Looking forward to the launch of ICESat-2 in late 2018, we anticipate that this new satellite laser altimetry mission will significantly improve our ability to resolve, comprehend, and model this feature.