Ranganathan, Meghana, Alexander A Robel, Alexander Huth, and Ravindra Duddu, April 2025: Glacier damage evolution over ice flow timescales. The Cryosphere, 19(4), DOI:10.5194/tc-19-1599-20251599-1619. Abstract
The rate of mass loss from the Antarctic and Greenland ice sheets is controlled in large part by the processes of ice flow and ice fracture. Studies have shown these processes to be coupled: the development of fractured zones weakens the structural integrity of the ice, reducing ice viscosity and enabling more rapid flow. This coupling may have significant implications for the stability of ice shelves and the rate of flow from grounded ice. However, there are challenges with modeling this process, in large part due to the discrepancy in timescales of fracture and flow processes and to uncertainty about the construction of the damage evolution model. This leads to uncertainty about how fracture processes can affect ice viscosity and, therefore, projections of future ice mass loss. Here, we develop a damage evolution model that represents fracture initiation and propagation over ice flow timescales, with the goal of representing solely the effect of damage on flow behavior. We then apply this model to quantify the effect of damage on projections of glacier response to climate forcing. We use the MISMIP+ benchmark glacier configuration with the experiment Ice1r, which represents grounding line retreat due to basal melt forcing. In this model configuration, we find that damage can enhance mass loss from grounded and floating ice by ∼ 13 %–29 % in 100 years. The enhancement of mass loss due to damage is approximately of the same order as increasing the basal melt rate by 50 %. We further show the dependence of these results on uncertain model parameters. These results emphasize the importance of further studying the multiscale processes of damage initiation and growth from an experimental and observational standpoint and of incorporating this coupling into large-scale ice sheet models.
Rifts are full-thickness fractures that propagate laterally across an ice shelf. They cause ice-shelf weakening and calving of tabular icebergs, and control the initial size of calved icebergs. Here, we present a joint inverse and forward computational modeling framework to capture rifting by combining the vertically integrated momentum balance and anisotropic continuum damage mechanics formulations. We incorporate rift–flank boundary processes to investigate how the rift path is influenced by the pressure on rift–flank walls from seawater, contact between flanks, and ice mélange that may also transmit stress between flanks. To illustrate the viability of the framework, we simulate the final 2 years of rift propagation associated with the calving of tabular iceberg A68 in 2017. We find that the rift path can change with varying ice mélange conditions and the extent of contact between rift flanks. Combinations of parameters associated with slower rift widening rates yield simulated rift paths that best match observations. Our modeling framework lays the foundation for robust simulation of rifting and tabular calving processes, which can enable future studies on ice-sheet–climate interactions, and the effects of ice-shelf buttressing on land ice flow.
Large tabular icebergs account for the majority of ice mass calved from Antarctic ice shelves, but are omitted from climate models. Specifically, these models do not account for iceberg breakup and as a result, modeled large icebergs could drift to low latitudes. Here, we develop a physically based parameterization of iceberg breakup based on the “footloose mechanism” suitable for climate models. This mechanism describes breakup of ice pieces from the iceberg edges triggered by buoyancy forces associated with a submerged ice foot fringing the iceberg. This foot develops as a result of ocean-induced melt and erosion of the iceberg freeboard explicitly parameterized in the model. We then use an elastic beam model to determine when the foot is large enough to trigger calving, as well as the size of each child iceberg, which is controlled with the ice stiffness parameter. We test the breakup parameterization with a realistic large iceberg calving-size distribution in the Geophysical Fluid Dynamics Laboratory OM4 ocean/sea-ice model and obtain simulated iceberg trajectories and areas that closely match observations. Thus, the footloose mechanism appears to play a major role in iceberg decay that was previously unaccounted for in iceberg models. We also find that varying the size of the broken ice bits can influence the iceberg meltwater distribution more than physically realistic variations to the footloose decay rate.
In December 2020, giant tabular iceberg A68a (surface area 3900 km2) broke up in open ocean much deeper than its keel, indicating that the breakage was not immediately caused by collision with the seafloor. Giant icebergs with lengths exceeding 18.5 km account for most of the calved ice mass from the Antarctic Ice Sheet. Upon calving, they drift away and transport freshwater into the Southern Ocean, modifying ocean circulation, disrupting sea ice and the marine biosphere, and potentially triggering changes in climate. Here, we demonstrate that the A68a breakup event may have been triggered by ocean-current shear, a new breakup mechanism not previously reported. We also introduce methods to represent giant icebergs within climate models that currently do not have any representation of them. These methods open opportunities to explore the interactions between icebergs and other components of the climate system and will improve the fidelity of global climate simulations.
