World ocean circulation diagnostically derived from hydrographic and wind stress fields: 1. The velocity field

Abstract

Using a robust diagnostic model, the steady circulation in the world ocean is determined from climatological annual mean fields of hydrographic data and wind stress. The upper circulation reflects the surface geopotential anomaly of the input hydrographic data. In addition, the “warm water route” is prominent: the water passing through the Indonesian seas flows westward across the Indian Ocean to return to the North Atlantic. In the deep Atlantic Ocean, the North Atlantic Deep Water is transported southward by the dominant deep western boundary current in the depth range from about 1500 m to the bottom, whereas the Weddell Sea Deep Water does not extend northward from the Argentine Basin. An important result is a westward current appearing near 25°N in the middepth Atlantic Ocean. Such a current has been inferred from tracer distributions but hardly detected with objective methods. The velocity maximum at middepth suggests that the current is not a lower part of a wind gyre but is a baroclinic flow caused by a thermohaline effect. In the Indian Ocean a swift middepth current appears along the western boundary, but it may be questionable because the resulting heat transport does not agree with earlier estimates. The deep water flowing into the southern basins from the Antarctic Circumpolar Current does not flow further northward even in the Madagascar Basin. The cause of these unsuccessful results is probably that the present model does not take into account large seasonal variations in the Indian Ocean.