An observational study of wave attenuation and wave-induced momentum transfer to sea ice in the marginal ice zone

Abstract

Momentum transfer from ocean waves to sea ice is a key fluid–structure interaction in the marginal ice zone, yet direct observational estimates of its magnitude remain scarce. We combine two independent networks of drifting buoys, six in the Barents Sea (winter 2021) and 65 around Svalbard (2022–2023), with ERA5 forcing and daily AMSR2 sea ice concentration. An estimator of the attenuation power law α(f) = a0fn requiring no sign selection, validated against synthetic spectra, gives n = 2.55 (95% confidence interval 2.28 to 2.82) in winter pack ice and 2.37 (1.58 to 3.46) in spring pack ice, against 5.29 (4.84 to 5.60) in one autumn new ice campaign: the exponent is regime dependent. In storms the ratio of wave to wind momentum input reaches 0.32 (90th percentile, 0.02 to 0.46) within 25 km of the ice edge and decays inward with a scale of 12 km (9 to 22) in the Barents network and 10 km (8 to 12) around Svalbard, both robust to a drag coefficient dependent on ice concentration and wind speed. The decay is faster than spectral attenuation predicts. Where wave and wind stresses are misaligned by over 45 degrees, the wind-only model residual grows with the wave stress (Spearman r = 0.50, 0.14 to 0.70). Among 85 candidate breakup events, the 43 in ice at concentrations of at least 50% show strains in the upper tail of the background distribution and a median concentration drop of 9 percentage points within three days.