Centered at the South Pole, Antarctica holds the largest expanse of continental ice on Earth, serving as the most significant reservoir of freshwater. This immense ice mass is in constant motion, deforming under the force of gravity and sliding over the bedrock beneath it. For years, Antarctica has been losing ice mass due to global warming. However, predictions about its future evolution and potential contribution to sea-level rise remain highly uncertain. One of the primary sources of uncertainty lies in understanding precisely how the ice slides at its base.
Basal sliding includes both the movement of ice over bedrock when the bed is hard and the deformation of sediments when the substrate is soft and deformable. In certain regions, particularly in fast-flowing areas known as ice streams, basal sliding is the dominant process driving ice motion. Since ice streams drain the majority of the ice sheet, gaining a better understanding of the mechanisms governing their movement is crucial.
Mathematically, basal sliding is described by a friction law that relates the basal stress (representing the resistance to ice motion due to the bed) to the basal ice velocity. This law can take different forms depending on the specific processes involved. In particular, subglacial water plays a key role in basal sliding by lubricating the bedrock and reducing the resistance of the till to deformation. It is typically incorporated into the friction law through a dependence on effective pressure, which represents the difference between the pressure in the ice and in the subglacial water system. This water originates from the melting of ice at the base and organizes into different types of drainage systems, classified as either inefficient or efficient. Inefficient systems are characterized by low-flow, diffuse drainage, whereas efficient systems exhibit high-flow, concentrated drainage in conduits.
In TC - A fast and simplified subglacial hydrological model for the Antarctic Ice Sheet and outlet glaciers, we developed, implemented, and tested a computationally efficient model for subglacial hydrology. This model can be fully coupled with an ice-flow model and accounts for several water-flow regimes (covering both inefficient and efficient drainage systems): flows in inter-clastic films and localized flows in canals over soft beds, as well as linked-cavity systems and localized flows in channels over hard beds. Our model also allows for heterogeneous beds composed of both rigid and deformable regions.
We tested the model on a century-scale timespan for Thwaites Glacier (West Antarctica). The results indicate that the hydrological system at the grounding line is a decisive factor in its retreat under climate forcing. Furthermore, our study demonstrates that deformable beds and efficient drainage systems at the grounding line slow down its retreat. In all scenarios, incorporating subglacial hydrology increases Antarctica’s projected contribution to sea-level rise. Overall, our paper underscores the importance of accounting for subglacial hydrology and bed properties in basal sliding -- factors that are often overlooked in current models. It is therefore crucial to improve our understanding of Antarctic basal conditions to enhance modeling of its future response to climate warming.
Do you want to read more? Check out the full paper: Kazmierczak, E., Gregov, T., Coulon, V., and Pattyn, F.: A fast and simplified subglacial hydrological model for the Antarctic Ice Sheet and outlet glaciers, The Cryosphere, 18, 5887–5911, https://doi.org/10.5194/tc-18-5887-2024, 2024. (link : https://tc.copernicus.org/articles/18/5887/2024/)
Written by Elise Kazmierczak
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