Publication Date:
2016-10-07
Description:
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.
Type:
Article
,
PeerReviewed
Format:
text
DOI:
10.1016/S0079-6611(01)00004-0
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