Effects of the atmospheric forcing resolution on simulated sea ice and polynyas off Adélie Land, East Antarctica

Pierre-Vincent Huot (1) , Christoph Kittel (2) , Thierry Fichefet (1) , Nicolas Jourdain (3) , Jean Sterlin (4) , Xavier Fettweis (2)

1 ELI - Earth and Life Institute [Louvain-La-Neuve]
2 Université de Liège
3 IGE - Institut des Géosciences de l’Environnement
4 UCL - Université Catholique de Louvain = Catholic University of Louvain

Coastal polynyas of the Southern Ocean play a central role in the ventilation of the deep ocean and affect the stability of ice shelves. It appears crucial to incorporate them into climate models, but it is unclear how to adequately simulate them. In particular, there is no consensus on the atmospheric forcing resolution needed to appropriately model the sea ice in coastal Antarctica. A high resolution might be required to represent the local winds such as katabatic winds which are key drivers of coastal polynyas. To fill in this gap, we have tested the sensitivity of sea ice and air-sea-ice interactions in a high-resolution ocean–sea ice model to the resolution of the atmospheric forcing. A set of regional atmospheric simulations at horizontal resolutions of 20, 10, and 5 km are performed with an atmospheric regional model and used to force three ocean–sea ice simulations in the Adélie Land sector, East Antarctica. Due to the better representation of topography with a refined grid, the o shore component of coastal winds becomes stronger at increased resolution. The wind intensification is particularly strong down valleys channelizing the katabatic flow, with increase in wind speed ranging between 1 and 3 m/s. Under a higher resolution forcing, polynyas open more frequently and are wider. This fosters the growth rate of sea ice in polynyas, while landfast ice and pack ice are weakly affected. In polynyas, the production of sea ice is increased by up to 30% at 5 km resolution compared to 20 km resolution. Polynyas downstream of the katabatic wind pathway are more affected than the ones driven by easterly winds, highlighting the importance of the local wind conditions. Brine rejection associated with these higher sea ice production rates affects the salinity budget of the ocean and enhances both the volume and density of the dense Shelf Water produced off Adélie Land. These results underpin the need to better account for local coastal winds and polynyas in ocean and climate models.

Mots clés: East Antarctica; Katabatic winds; Polynyas; Dense Shelf Water; Landfast ice; High resolution

Domaines: Océan, Atmosphère; Glaciologie

Pierre-Vincent Huot, Christoph Kittel, Thierry Fichefet, Nicolas Jourdain, Jean Sterlin, et al.. Effects of the atmospheric forcing resolution on simulated sea ice and polynyas off Adélie Land, East Antarctica. Ocean Modelling, 2021, 168, pp.101901. ⟨10.1016/j.ocemod.2021.101901⟩. ⟨hal-03456196⟩