%======================================================================
%                    H Y D / F _ R E G I O N A L . T E X 
%                    doc: Wed Apr  8 09:11:08 1998
%                    dlm: Mon Jun  5 18:43:59 2000
%                    (c) 1998 A.M. Thurnherr
%                    uE-Info: 36 13 NIL 0 0 72 3 2 4 ofnI
%======================================================================

\begin{table}[t]
\begin{center}
\begin{tabular}{|rrrl|}
\hline 
%----------------------------------------------------------------------
\SigmaTwo & \SigmaTheta & Depth & Relevance \\ \hline\hline
%======================================================================
36.20 & 27.37 &  \m{780} & top of Mediterranean outflow water \\
36.60 & 27.68 & \m{1120} & Mediterranean water salinity maximum \\
36.82 & 27.79 & \m{1500} & \MAR crest \\
36.93 & 27.82 & \m{2000} & ``bifurcation depth'' \protect\rsec{hydraulics} \\
%----------------------------------------------------------------------
\hline
\end{tabular}
\end{center}

\caption[\A depths and potential densities]{Key depths and potential
densities referenced to the surface (\SigmaTheta) and to \dbar{2000}
(\SigmaTwo); $\sigma$-units are omitted.} \label{tab:sig}

\end{table}

%----------------------------------------------------------------------

%--------------------
\begin{figure}[t]

\placeFig{HYD/AC}

\caption[1997 near-surface flow observations]{Mean LADCP-derived flow
speeds and directions in the top \m{1000} of the water column; each
data point represents a \m{50} vertical mean.}

\labelFig{AC}

\end{figure}
%--------------------

The \A segments are located in a section of the MAR with a complex
hydrography which is affected by the ridge topography, the
Mediterranean water tongue and the Azores Current and Front
\citeEG{JGR/wilson+95}. (For comparison with other studies some key
potential densities referenced to \dbar{2000} (\SigmaTwo) and to the
surface (\SigmaTheta), together with the associated depths estimated
from the pressure-averaged CTD profile of the entire survey, are
listed in \callout{\rtabNP{sig}}.)

% - Med-Water

In full-depth hydrographic profiles the Mediterranean water tongue is
immediately apparent as a region of nearly constant salinity in the
\ThetaTwo (potential temperature referenced to \dbar{2000}) range of
\degC{7.5$--$9.5} (e.g.\ \rfigNP{F-tscompare} below). The mean salinity
maximum of \psu{35.42} has an associated potential density \SigmaTwo of
\kgpmmm{36.6} (\SigmaTwo units will be omitted below). These values are
consistent with published data of the Mediterranean water tongue in
this region \citeEG{DSR/sy88}. The horizontal distribution of the
Mediterranean outflow water can be traced as a wedge penetrating deep
into the North Atlantic well beyond the MAR (e.g.\
\MakeLowercase\figurename~69 of \citeNP{Progress/fukumori+91}).
According to \citeN{DSR/sy88}, this wedge is bounded by two main
branches of the Gulf Stream extension: the North Atlantic Current to
the north (\degN{\approx\!46}) and the Azores Current to the south.
While the North Atlantic Current flows too far north to influence the
\A segments, the latitude of the Azores Current near \degW{34} is not
well defined. There is considerable evidence for meanders on a scale of
at least \km{100}
\citeEG{Progress/gould85,DSR/sy88,DSR/fernandez+pingree96}.

% - Azores current
% - Azores front

\callout{\rFigNP{AC}} shows the mean flow velocities in the top
\m{1000} of the water column, derived from the LADCP profiles of all
CTD stations. The flow is mainly SE-ward with the speed decreasing
nearly linearly from \mps{0.17} at the surface to \mps{0.05} at
\m{1000}. Below \m{1000} the mean speed remains approximately constant
down to the depth where the topography begins to influence the flow
(see \rfigNP{meancur}). The magnitude and vertical structure of the
observed current are consistent with geostrophic calculations presented
by \citeN{Progress/gould85} and by \citeN{DSR/sy88}, both reporting
velocities around \mps{0.25} at the surface decreasing nearly linearly
to \mps{0.05} at \m{1000} in the vicinity of the \A segments.
\citeN{Progress/gould85} also proposes two criteria to assess if a
given station lies north or south of the Azores Front, one for the
depth of the \degC{15} isotherm (less than \m{300} with typical values
around \m{100} north of the front) and the other for the surface
salinity (less than \psu{36.4} with typical values near \psu{36.2}
north of the front). For the data of the 1997 survey the respective
mean values are \m{280} and \psu{36.3}, indicating that the frontal
region was sampled. The hydrography and current measurements of the \F
cruise are therefore consistent with a SE-ward flowing meander of the
Azores Current influencing the top \m{1000} of the water column.

