Internal fluctuations in an ocean-atmosphere box model with sea-ice

Abstract

 An ocean-atmosphere box model is presented where the polar ocean box is of variable extent and may be covered with ice. Ice thickness and temperature are predicted on the basis of a simple thermodynamic sea-ice model. The stimulation of internal variability by sea-ice is explored. Experiments are conducted with the full model but also with model versions where atmospheric and oceanic transport processes are partly suppressed. Moreover, reduced versions of the sea-ice model are tested. Some of the resulting climate states exhibit little internal variability and a steady growth of ice thickness. However, a wide range of internal fluctuations is generated in other runs. These include quasiperiodic oscillations where ice-free phases alternate with ice-covered states and chaotic behaviour. It is a key result that the choice of the sea-ice model has a profound impact on the fluctuations.