Circumpolar Effects of a Velocity‐Restoring Scheme for Antarctic Fast Ice on Shelf Waters and Ice Shelf Melt Simulated by NEMO4‐SI <sup>3</sup>
(2026) Journal of Geophysical Research: Oceans — Vol. 131, n° 10, p. 1-28 (2026)
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JGR Oceans - 2026 - Pirlet - Circumpolar Effects of a Velocity‐Restoring Scheme for Antarctic Fast Ice on Shelf Waters and.pdf
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- Authors
Vancoppenolle, M 
Jourdain, N
- Abstract
- Dense water formation in the Southern Ocean plays a key role in the global ocean overturning circulation, affecting the distribution of heat, carbon, oxygen, and nutrients. Fast ice stays immobile while blocking sea ice flow, favoring the opening of coastal polynyas, where intense air-sea exchanges drive sea ice production and ocean densification. Antarctic fast ice representation is notoriously poor in Earth system models, and is thus considered a potential cause of model biases in dense water formation. Here we assess the impact of a sea ice velocity-restoring representation of Antarctic fast ice on Antarctic shelf water properties and ice shelf melt using NEMO4-SI 3 simulations with and without velocity-restoring. By improving the location and shape of coastal polynyas, fast ice redistributes sea ice production and promotes Dense Shelf Water formation in several key source regions. In contrast, beneath extensive fast ice tongues, the reduced brine rejection associated with lower sea ice production limits mixed layer deepening, leading to fresher surface waters, which are then advected into downstream polynyas. The enhanced upper-ocean stratification beneath fast ice isolates warm subsurface waters from the surface and favors their intrusion into nearby ice shelf cavities, increasing ice shelf basal melt. As a result, ice shelf basal melt increases overall by 15.8% in the simulation including fast ice. These results support that ESMs studies with an Antarctic focus would gain from a physically-based representation of Antarctic fast ice. Plain Language Summary The Southern Ocean around Antarctica is key to the global climate system. In this region, dense water forms on the continental shelf and sinks to the deep ocean, carrying heat, carbon, oxygen, and nutrients around the globe. The ocean also melts Antarctic ice shelves-large, floating extensions of the Antarctic ice sheet. Earth system models (ESMs) try to represent these processes but often do so inaccurately. One important issue is that most models neglect fast ice, immobile sea ice attached to the coast, grounded icebergs, and the Antarctic ice shelf calving fronts. Fast ice strongly influences nearby areas of open-water, called coastal polynyas, which are important sites for sea ice growth and the formation of dense water. In this study, we add a representation of fast ice in an ocean-sea ice model and examine how it affects Antarctic shelf waters. We find that adding fast ice makes shelf waters denser in some areas, but fresher beneath and downstream of long stretches of fast ice. Overall, representing fast ice increases the ice shelf melt rate. Our results show that ESMs would gain in realism on the Antarctic continental shelf with a proper representation of fast ice.
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Citations
Pirlet, N., Fichefet, T., Vancoppenolle, M., De Lavergne, C., & Jourdain, N. (2026). Circumpolar Effects of a Velocity‐Restoring Scheme for Antarctic Fast Ice on Shelf Waters and Ice Shelf Melt Simulated by NEMO4‐SI <sup>3</sup>. Journal of Geophysical Research: Oceans, 131(10), 1-28. https://doi.org/10.1029/2025jc023673 (Original work published 2026)