EFFECTS OF A CONCAVE BOTTOM GEOMETRY ON THE UPWELLING-DRIVEN CIRCULATION IN AN ABYSSAL OCEAN-BASIN

Bottom water circulation in a bowl-shaped, or concave, abyssal basin driven by upwelling is investigated using a simple numerical model. In a basin wholly contained in one hemisphere, the concave bottom geometry introduces a strong topographic beta effect around the rim of the basin. Also, the character of the circulation is fundamentally altered from the circulation pattern in a flat bottom basin, where a sluggish northeastward interior flow is compensated by a strong western boundary current, to a basinwide cyclonic recirculation of a substantially greater strength without western intensification. In contrast, circulation in a similar basin that straddles the equator fails to show a significant difference from the circulation in a flat bottom basin. This dichotomy between equatorial and midlatitude basins can be understood in terms of the geometry of the underlying geostrophic contours.