Arctic sea-ice cover from the early Holocene: the role of atmospheric circulation patterns

Proxy evidence suggests that a mean atmospheric state, reminiscent of the positive phase of the North Atlantic/Arctic Oscillation (NAO), persisted throughout the early Holocene and resulted in a dipole pattern in sea-ice concentration between the north-eastern and north-western North Atlantic. A dynamic thermodynamic coupled sea-ice–ocean model is used to simulate the sea-ice concentration and thickness in the Arctic during the early Holocene. It is forced with winds, ocean currents and surface air temperatures (SAT) from recent years with a positive phase of the NAO in conjunction with altered long and shortwave radiation and surface air/ocean temperatures. The simulation reproduces an east/west dipole in sea-ice cover of the Arctic and is compatible with reconstructed sea-ice conditions in the Chukchi Sea (inferred from dinoflagellate cyst analysis of ocean sediment cores). Sensitivity studies were performed to investigate the individual effects of radiation, ocean forcing, SAT and winds on sea-ice cover. Results show that in the East Siberian Sea, SAT is the dominant forcing for changes in sea-ice thickness, whereas winds and SAT are the dominant factors in sea-ice concentration anomalies. In the Barents Sea, sea-ice anomalies are influenced by air and sea surface temperatures, and ocean currents.