Robust Regional Contrast but Penetration-Sensitive Snow Thickness Over Sea Ice From Multi-Winter Antarctic CRYO2ICE Observations

Abstract

Snow on Antarctic sea ice modulates albedo, thermodynamic growth, and snow–ice formation, yet remains a leading uncertainty in altimetry-derived sea-ice thickness. Here we use the post-2022 CRYO2ICE configuration to derive along-track winter snow thickness from ICESat-2 laser and CryoSat-2 Ku-band radar freeboards over the Weddell and Ross sectors. We analyze 82,341 winter matchups (August 2022–September 2025) using a 5 km, 4 hr collocation criterion and propagate freeboard and snow-density uncertainties. Retrieved snow thickness is consistently larger in the Weddell Sea (mean 0.255 m, median 0.188 m) than the Ross Sea (0.217 m, 0.156 m), consistent with the older, thicker western Weddell ice. The contrast persists across sampled months and years and under common snow-density and penetration-factor assumptions. Formal per-matchup precision (0.039–0.040 m) is dominated by CryoSat-2 radar-freeboard uncertainty, whereas the absolute magnitude is set by the unresolved Ku-band scattering horizon. Comparison with AMSR2 passive-microwave snow depth shows weak point-to-point agreement ($r^2=0.062$ and in the Weddell and Ross sectors), reflecting differing measurement physics and spatial support. Nevertheless, both independently reproduce thicker Weddell than Ross snow. Under a common penetration factor, absolute sector-mean snow thickness varies by approximately a factor of two across the tested range, whereas the sector ordering is preserved under any uniform choice of penetration factor. CRYO2ICE therefore resolves a repeatable regional freeboard-difference signal, but conversion of that signal to absolute snow thickness remains conditional on the poorly constrained, ice-regime-dependent Ku-band scattering horizon.