A first evaluation of wave-ice interactions on the global mass balance

Vancoppenolle, Martin Fichefet, Thierry [UCL] Ackley, Steve Shen, Hayley Massonnet, François [UCL] Mathiot, Pierre [UCL] Lecomte, Olivier [UCL]

Sea ice frequently forms in wavy waters. Wave motion packs forming ice crystals into small floes, while the ice attenuates the waves as the ice floes increase in diameter and thickness. Swell has been reported up to a few hundred kilometres inside the ice pack. Because of ocean waves, young ice floes take a rounded shape that led hungry early explorers to give them the name of pancake ice. Observations suggest that pancake ice thickness grows up to twice as fast as for ice forming in quiet seas. In this work we try to evaluate whether future large-scale sea-ice models should include wave–ice interactions to properly simulate large-scale distributions of ice concentration and thickness. In the large-scale 3-D ice–ocean modelling system NEMO-LIM, a representation of pancake ice formation is included. First, the ERA-40 ocean wave climatology is extrapolated in the sea-ice zone as if the ocean was ice-free. After diagnosing the simulated ice edge, ocean waves are propagated from the ice edge further inside the ice pack assuming exponential decay of amplitude. Finally, the thickness of newly forming ice is computed as a function of wave amplitude, as given by the equilibrium pancake ice theory. Wavelength is prescribed, which is a strong limitation of the model. In the model, pancake ice formation is found important in regions located in the vicinity of open ocean, namely the Southern Ocean and, in the Arctic, the Bering, Okhostk and Greenland Seas. Pancake ice formation accelerates the ice-edge progression, reduces winter ice concentration and, in turn, enhances ice production and thickness, in particular in the Southern Ocean. In some regions, the ocean responds to changes in ice production and modifies the location of the ice edge, as in East Antarctica. Wave–ice interaction parameters (wave attenuation, equilibrium pancake thickness, …) have a key impact on the simulated response of the model. Given the uncertainty in the model parameters, we conclude that more work is required to couple ocean waves and sea ice in large-scale models.