%======================================================================
%                    I N T R O / A M A R . T E X 
%                    doc: Tue Nov 16 14:14:02 1999
%                    dlm: Wed Jun  7 21:50:40 2000
%                    (c) 1999 A.M. Thurnherr
%                    uE-Info: 76 54 NIL 0 0 72 3 2 4 ofnI
%======================================================================

\begin{figure}[t]

\placeFig{intro/AMAR_location}

\caption[\A segment location]{Location of the \A segments (star); solid
lines indicate the boundaries between the European, African and North
American tectonic plates.}

\labelFig{AMAR-loc}

\end{figure}

\begin{figure}[t]

\placeFig[.9]{intro/AMAR_bridge}

\caption[\A bathymetry (high resolution)]{High-resolution (nominally
\m{100}\m{\times100}) \A bathymetry; intermediately dark shaded regions
are deeper than \m{2500}, lightly shaded regions are between \m{2000}
and \m{2500}, and unshaded regions are less than \m{2000} deep; contour
interval is \m{500}; dark shaded regions without contours are regions
without data.}

\labelFig{AMAR-bridge}

\end{figure}

\begin{figure}[t]

\placeFig[.9]{intro/AMAR_SS97}

\caption[\A bathymetry (low resolution)]{\A bathymetry extracted from
the \protect\citeN{JGR/smith+sandwell97} data set
(\arcmin{2}\arcmin{\times\,2} resolution at the equator), derived from
gravity anomalies constrained by ship tracks; shading and contours are
the same as in \protect\rfigNP{AMAR-bridge}.}

\labelFig{AMAR-SS97}

\end{figure}

\rFigNP{AMAR-loc} indicates the location of the \A (ALVIN Mid-Atlantic
Ridge) segments of the MAR. \rFigsNP{AMAR-bridge}{AMAR-SS97} show their
bathymetry extracted from two different data sets. (Because the data
sets are mutually consistent they were combined e.g.\ for
\protect\rfigNP{F2-stations}.) The rift valley runs from the southwest
(SW) to the northeast (NE). The non-transform discontinuity near
\latN{36}{15} separates the ridge into two segments: \A to the NE and
\sA to the SW. The approximate lengths of the two segments are \km{100}
\sAp{(}{)} and \km{50} \Ap{(}{)}. \citeN{JGR/detrick+95} further
subdivide \sA into three segments (PO-5, PO-6 and PO-7 in their
terminology); PO-5 was previously called \emph{AMAR Minor}, but
subsequent sidescan sonar investigation has revealed no magmatic
evidence to support this distinction as an additional ridge segment
\perscomm{C.R.\ German}.

The rift-valley floor of the \A segments is characterized by a number
of deep ``basins'' (defined here as depressions below \m{2500})
connected by shallower regions. On both sides of the valley the walls
rise to depths above \m{2000}. Below \m{2000} there is a sill
connecting \sA to the \emph{North Oceanographer} segment near
\latN{35}{40}/\lonW{34}{40} (minimum depth \m{2200}). North of \A the
rift valley continues in the \emph{FAMOUS} (French-American Mid-Ocean
Undersea Study) segment, connected to \A at the sill near
\latN{36}{35}/\lonW{33}{30} (minimum depth \m{2200}). Another sill near
\latN{35}{35}/\lonW{34}{10} (minimum depth \m{2300}) connects the \sA
rift valley to the eastern ridge flank. There may also be a connection
between the \A rift valley and the western ridge flank below \m{2000}
near \latN{36}{40}/\lonW{34}{00} but the available bathymetric data are
ambiguous (neither data set indicates a connection below \m{2100},
however).

