Reversability of arctic sea ice retreat - A conceptual multi-scale modeling approach

The ice-albedo feedback has been identified as an important factor in the decay of the Arctic sea ice cover in a warming climate. Mechanisms of transition from perennial ice cover to seasonal ice cover are discussed in the literature; the existence of a tipping point is disputed. A newly developed regular network model for energy exchange and phase transition of an ice covered ocean mixed layer is introduced. The existence of bistability, a key ingredient for irreversibility, on local and regional scales is explored. It is shown in a spatially confined model that the asymptotic behavior and the existence of a parameter region of bistability strongly depend on the albedo parametrization. The spatial dynamics of sea ice retreat are studied for a high resolution latitudinal model of the ocean mixed layer. This regional model suggests that sea ice retreat is reversible. It is shown that laterally driven melt of thick multi-year sea ice, and thus, ice-albedo feedback, is an important mechanism in the transition from perennial to seasonal ice cover at the pole. Results are used to interpret observed changes in the recent ice extent and ice volume record. It is shown that the effectiveness of ice-albedo feedback strongly depends on the existence of lateral heat transfer mechanisms in the ocean.