On the role of the Azores Current in the ventilation of the North Atlantic Ocean

New, A.L., Jia, Y., Coulibaly, M. and Dengg, J. (2001) On the role of the Azores Current in the ventilation of the North Atlantic Ocean. Progress in Oceanography, 48 (2-3), 163-194. (doi:10.1016/S0079-6611(01)00004-0).

Abstract

Three high-resolution ocean circulation models of the North Atlantic, differing chiefly in their description of the vertical coordinate, are used to examine the ventilation of the North Atlantic subtropical gyre. All the models produce mode waters of realistic densities in the Sargasso Sea and the European Basin, but have Azores Currents of differing strengths, which are categorised as strong (of realistic transport), intermediate, and weak. These differences have a critical impact upon the ventilation of the gyre. Most importantly, the strong Azores Current forms an effective barrier to the southward ventilation of Eastern North Atlantic Water from the northern European Basin, initially driving it southwestwards into the central gyre, before turning it back eastwards again in a general cyclonic circulation north of the Current. The intermediate and weak Azores Currents instead allow the southward ventilation of this water mass near the European and African coasts. The situation in Nature appears to be intermediate between these two cases, with the Azores Current acting as a partial block. The study also raises the possibility of the Azores Current forming an advective connection between the Sargasso Sea Mode Waters in the western basin and modes of similar densities found in the eastern basin on the southern side of the Current. Although there are high levels of variability in the extent of these lighter modes in the eastern basin in Nature, this postulate is supported by a number of observational studies. In addition, the present study also provides some support for the local production of Madeira Mode Water in the eastern basin, associated with retroflecting current branches on the southern side of the Azores Current. Overall, the Azores Current is, therefore, likely to have a critical impact upon the ventilation of the subtropical gyre over a large area, rather than just locally, affecting the potential vorticity and density structure of the upper ocean between subtropical latitudes and the northern European Basin. The study also contributes to an ongoing community effort to assess the realism of our current generation of ocean models.

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