This paper investigates the long-term impact of sea ice on global climate
using a global sea-ice–ocean general circulation model (OGCM). The sea-ice
component involves state-of-the-art dynamics; the ocean component consists
of a 3.5° × 3.5° × 11 layer primitive-equation model. Depending on the
physical description of sea ice, significant changes are detected in the
convective activity, in the hydrographic properties and in the thermohaline
circulation of the ocean model. Most of these changes originate in the
Southern Ocean, emphasizing the crucial role of sea ice in this marginally
stably stratified region of the world's oceans. Specifically, if the effect
of brine release is neglected, the deep layers of the Southern Ocean warm up
considerably; this is associated with a weakening of the Southern Hemisphere
overturning cell. The removal of the commonly used “salinity enhancement”
leads to a similar effect. The deep-ocean salinity is almost unaffected in
both experiments. Introducing explicit new-ice thickness growth in partially
ice-covered gridcells leads to a substantial increase in convective
activity, especially in the Southern Ocean, with a concomitant significant
cooling and salinification of the deep ocean. Possible mechanisms for the
resulting interactions between sea-ice processes and deep-ocean
characteristics are suggested.