Increased horizontal resolution provides limited benefits for simulated Arctic and Antarctic sea ice climatology and recent extremes in a NEMO4-SI3 hierarchy

Abstract. We assess the sensitivity of Arctic and Antarctic sea ice simulations to horizontal resolution using an ocean-sea ice NEMO4-SI3 hierarchy at 1°, 1/4° and 1/12° nominal resolutions, but with identical vertical resolution, forced by the ERA5 atmospheric reanalysis. Increased resolution improves selected regional and seasonal features, particularly where ocean circulation strongly controls the sea ice edge. In the Arctic, improvements are modest and mainly occur in the Greenland Sea, where the higher-resolution configurations (1/4° and 1/12°) better represent Atlantic inflow west of Svalbard and reduce the excessive winter ice extent simulated at 1°. In the Antarctic, the response is more widespread. Higher horizontal resolution improves the winter ice edge downstream of major bathymetric features, while the 1/4° configuration also improves austral summer sea ice extent and thickness in the Weddell and Ross Seas. Additionally, the 1/12° configuration enhances vertical mixing with warm subsurface waters, promoting thinner ice and a more poleward ice margin. Overall, across both poles, resolution does not systematically improve sea ice extremes or hemispheric biases and benefits depend strongly on the diagnostic considered.