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%                    P L U M E / F L A M E 2 . T E X 
%                    doc: Mon Mar  6 20:19:49 2000
%                    dlm: Wed Jun  7 23:17:10 2000
%                    (c) 2000 A.M. Thurnherr
%                    uE-Info: 85 63 NIL 0 0 72 3 2 4 ofnI
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\begin{figure}[t]

\placeFig{plume/F2_plume3d}

\caption[1998 particle plume (plan view)]{Depth-integrated
(\m{1800$--$2500}) nephelometry profiles of the \FF (1998) data set
(arbitrary vertical scale); bathymetric contour interval is \m{250};
thin bars denote profiles without plume signals (from visual
inspection).}

\labelFig{F2-plume3d}

\end{figure}

During the 1998 survey 10 CTD stations were occupied in the \R region
\rfig{F2-stations}. The variability of the particle distribution
observed in 1997 \rfig{F-plume3d} implies that the 1998 data set is not
sufficient to derive an integrated view of the hydrothermal plume.
\rFigNP{F2-plume3d} shows the horizontal distribution of the
depth-integrated nephelometry profiles. Because of the different
instruments used during the two surveys \rsecs{F-methods}{F2-methods}
the optical responses cannot be compared directly. Nevertheless, there
are qualitative differences between the particle distributions observed
during the two surveys. The strongest particle anomalies in 1998 were
recorded SW of the vent field where no plume signatures had been
observed in 1997 (c.f.\ \rfigNP{F-plume3d}).%
 %
%--------------------
\begin{figure}[t]

\placeFig{plume/F2_nephprofs}

\caption[1998 nephelometry profiles]{Selected \FF nephelometry
profiles, including the one closest (\km{1.5} distance) to the vent
field \npa, one from the saddle of \RS \npb, one from the embayment
east of \RR \npc, and two from the interior of the SW basin \npd \&
\npe; successive profiles are horizontally offset by \V{0.5}.}

\labelFig{F2-nephprofs}

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

\placeFig{plume/F2_PVD_G}

\caption[1998 flow near vent field (last week)]{Progressive vector
diagrams showing the last full week of hourly flow measurements at
mooring G \protect\rfig{CM-stations}; symbols are drawn at midnight
GMT.}

\labelFig{F2-PVD-G}

\end{figure}
%--------------------
 %
\rFigNP{F2-nephprofs} shows a selection of the individual nephelometry
profiles. The rise height of the plume is not well defined but the main
particle anomalies NE of the vent field (\sfa and \sfb) are observed
below \m{2000} whereas the plume in the interior of the SW basin (\sfd
and \sfe) spans the depth range between \m{1800} and \m{2150}, i.e.\ up
to \m{100} shallower than the highest light-scattering anomalies
observed in 1997. The current-meter data shown in \rfigNP{F2-PVD-G}
provide a plausible explanation for the observed particle distribution.
In the week prior to the 1998 survey the velocity field near the plume
source was strongly sheared with mean NE-ward and SW-ward flows at
\m{2300} and \m{1800}, respectively. The buoyant plumes rising into
this sheared current field were therefore bisected with only the upper
(i.e.\ more buoyant) portions reaching the SW-ward flow regime. (It
will be noted that profile \sfc of \rfigNP{F2-nephprofs} from the
embayment east of \RR contains weak particle anomalies up to \m{1800}.
From our data the origin of these particles cannot be determined.) The
limited sampling achieved during the 1998 survey is insufficient to
determine the pathways of the particles beyond the immediate vicinity
of \RR. It is also not clear if the range in magnitude of the observed
light-scattering anomalies is representative, but it does not appear
unreasonable that water parcels with the highest concentrations of
hydrothermal effluents (indicated by high particle loads; c.f.\
\rchapNP{NESPI}) rise highest, as \rfigNP{F2-nephprofs} appears to
suggest.

