The Glacial Ocean: A Study with a Zonally Averaged, Three-Basin Ocean Circulation Model

Abstract

A zonally averaged primitive equation model is developed to investigate the oceanic general circulation of the last glacial maximum. The Atlantic, Indian, and Pacific basins are separately resolved, and they are connected in the Southern Hemisphere by a circumpolar channel through which mass, heat, and salt are exchanged. The model circulation is driven, in addition to wind forcing, by restoring the sea-surface temperature and salinity to prescribed values. Under present-day boundary conditions, the model reproduces the global conveyor belt: deep water is formed in the Atlantic between 60 and 70°N and in the vicinity of Antarctica, while the Indian and Pacific basins show broad upwelling. The simulated temperature and salinity fields and the computed meridional heat transport are in general agreement with the observational estimates. When glacial conditions for temperature and salinity are used to force the model, significant changes occur in the circulation patterns. Most of the deep Atlantic is filled with water originating from the model Southern Ocean. Deep-water production completely stops between 60 and 70°N in the Atlantic. However, the surface-water salinity around 50°N is sufficiently high to permit deep convection to a maximum depth of 2000 m, as a source of intermediate and deep waters. Open convection occuring between 30 and 40°N, contributes to the ventilation of these waters. In the North Pacific, the model simulates a weak intensification of the intermediate-water production. Another prominent feature is that the modelled global ocean deep-water temperature is about 2°C lower than for present-day boundary conditions. It is worth pointing that all these changes compare favourably with the existing geological reconstructions.