The Water Masses of the Central North Atlantic in 1983—84

Abstract

Hydrographic surveys carried out in 1983?84 along both sides of the Mid-Atlantic Ridge between 24° and 53°N provide a detailed description of the well-known North Atlantic water masses with particular emphasis on their meridional distribution and zonal dissymetry. In the upper layers the dense horizontal sampling resolves the several narrow Gulf Stream extensions into the ocean interior, giving the image, in the Central Water density range, of a mosaïc of mode waters separated by fronts. At intermediate depths a vertical shear in the distributions of the Mediterranean Water and Labrador Sea Water stands out, both water masses having their lower part displaced southwards relative to their upper parts. Bottom waters containing nearly 20 percent of pure Antarctic Bottom Water are observed at 50°N in the eastern basin, in contrast with the western basin where proportions greater than 10 percent were found only south of 36°N along our section. This water mass analysis also gives indications that strong mixing occurs at several water mass boundaries: between Subarctic Intermediate Water and (i) North Atlantic Central Water, (ii) Mediterranean Water, and between Antarctic Bottom Water and the overlying waters.