The heat budgets of an ice-free and an ice-covered Arctic Ocean

Tentative estimates of heat budgets of the Arctic Ocean are based on incomplete observational data and certain subjective assumptions, but they appear to be justifiable in the light of present knowledge. The thermal regime of the present North Polar Sea is controlled to a large extent by the essentially permanent ice cover (mean albedo about 61%). Additional factors influencing present surface temperature are ocean current heat flux (gain) long-wave radiation (loss), and evaporation and sensible heat (loss). These factors yield a net balance for the present of 0.01×1021 cal/yr for the polar sea. The combined surface-atmosphere heat balance involves the additional terms for advection and atmospheric radiation to space. The changes consequent upon the disappearance of the polar sea ice involve a decrease of albedo to an estimated 10% (with consequent increased absorption of insolation) an increased greenhouse effect related to greater cloud cover and more humid air, a decrease in heat loss from evaporation and sensible heat transfer. The evaluation of these factors yields a net annual heat balance for the ice-free polar sea of 2.63×1021 cal if a temperature of 0°C is assumed for the water surface. The increased radiation from the warmer, more extensive cloud cover is included in the estimation of the combined heat balance of the ocean-atmosphere system. If the present ice cover disappears, as it might have in the past, these calculations support the possibility of a stable ice-free surface until a change occurs in the factors that affect the heat balance.