Dependence of the Arctic Ocean ice thickness distribution on the poleward energy flux in the atmosphere

Abstract

The sensitivity of the Arctic Ocean ice cover on the atmospheric poleward energy flux, D, is studied using a coupled column model of the ocean, ice, and atmosphere. In the model, the ice cover is described by a thickness distribution and the atmosphere is a simple two-stream gray body in radiative equilibrium. It is shown that the thickness distribution, in combination with the albedo function, gives a strong nonlinear response to positive perturbations of D. The response on D is sensitive to the albedo parameterization and the shape of the thickness distribution, controlled by ridging and divergence. An increase of about 9 W m-2 from a standard value of D = 103 W m-2 has a dramatic effect, reducing the ice thickness by more than 2 m, and generates a large open-water fraction during summer. The reduction of ice thickness is characterized by a clear transition between two regimes, going from a regime where first-year ice survives the next summer melt period to a seasonal ice regime where the first-year ice melts completely. It is shown that the existence of seasonal ice regime is dependent on the surface mixed layer thickness. The model enters a completely ice-free state if the thickness of the mixed layer is increased above a threshold value. The adjustment timescale for the ice cover is 6 years for small positive and negative perturbations in D. For larger positive perturbations of about 10 W m-2, the adjustment timescale is up to 20 years.