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%                    I N T R O / R A I N B O W . T E X 
%                    doc: Tue Nov 16 14:14:02 1999
%                    dlm: Wed Jun  7 21:52:07 2000
%                    (c) 1999 A.M. Thurnherr
%                    uE-Info: 32 21 NIL 0 0 72 3 2 4 ofnI
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\begin{figure}[t]

\placeFig[.9]{intro/Rainbow_geography}

\caption[\R hydrothermal vent-field location]{\R region bathymetry and
nomenclature; shading is the same as in \rfigNP{AMAR-bridge}; contour
interval is \m{250}; the black cross near the \m{2250} contour marks
the location of the vent field; the two deep basins are part of the
median valley running SW--NE; the unshaded regions in the SE and NW
corner form part of the rift-valley walls.}

\labelFig{Rainbow-geography}

\end{figure}

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

% - Intro to Rainbow

The \R hydrothermal plume was discovered during a large-scale survey of
the \MAR near the non-transform discontinuity separating the \sA and
the \A segments \cite{EPSL/german+96}. There, the rift valley is
blocked by a small ridge \RRp{(}{;} minimum depth \m{1950}) and an
adjacent sill \RSp{(}{;} minimum depth \m{2500}), separating it into a
SW and a NE basin \callout{\rfig{Rainbow-geography}}. Based on
water-column light-transmission anomalies, the site was chosen for a
preliminary study using 7 CTD casts \cite{GRL/german+96} and for
testing the \BGT tow-yo platform which was used to map the hydrothermal
plume over a horizontal extent of \km{10$--$15} \cite{EOS/rudnicki+95}.
The particle plume was observed to rise to a depth of \m{2000$--$2100},
i.e.\ it was confined within the rift valley. Based on these
observations the \emph{FLAME} project \rsec{motivation} was initiated
to investigate the hydrography, plume dynamics, chemistry, and biology
of the \R site. Preliminary findings from the first \F cruise
\rsec{F-methods} were reported by \citeN{EPSL/german+98}. During a
subsequent submersible dive the active hydrothermal vent field was
discovered at a depth between \m{2270} and \m{2320} at
\latN{36}{13.80}, \lonW{33}{54.12} \cite{misc/fouquet+98}.