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%                    D I S C U / R E S U L T S . T E X 
%                    doc: Tue Mar 28 18:04:16 2000
%                    dlm: Thu Jun  8 00:31:24 2000
%                    (c) 2000 A.M. Thurnherr
%                    uE-Info: 143 50 NIL 0 0 72 3 2 4 ofnI
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\subsection{Observations}

\subsubsection{Rift-Valley Flow and Hydrography}

\begin{enumerate}

\item Persistent unidirectional flow was observed in the rift-valley of
the \A segments during a full year (1997--1998). The along-valley
transport remained surprisingly constant in spite of a warming event
shifting the flow patterns.

\item A range of processes potentially associated with high rates of
diapycnal mixing were observed, including hydraulically controlled
cross-sill flows, topographic lee waves, and strong tidal currents. 

\item In the vicinity of eastern boundaries and on the saddle of a sill
the flow energy was dominated by the lowest-frequency components.
Elsewhere the semi-diurnal tide dominated with a range of additional
energetic oscillations characterized by periods between \h{4} and
\d{14}.

\item Except at the lowest frequencies the flow energy was dominated by
the clockwise rotary component with the polarization decreasing with
increasing depth.

\item In 1998 along-valley hydrographic gradients extending throughout
the segments were observed. Historical data are consistent with similar
gradients in the \A segments in 1992 and in the rift valley of a
segment near \degN{45} in 1979.

\item Volume-flux budgets of the \A segments indicate that there may be
loss of water from the flow below \m{2000}.

\item The convective heat flux from the \R hydrothermal vent field
together with conductive geothermal heating along the entire \A
segments provide less than 10\% of the thermal energy required to close
the heat budgets of the rift valley.

\item Assuming that the heat budgets are balanced by diapycnal mixing
yields bulk diffusivity estimates of order \mmps*{5}{-3}.

\end{enumerate}

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\subsubsection{Basin/Sill Systems}

\begin{enumerate}

\item Simple basin/sill combinations act as effective low-pass filters
with time scales determined by the storage capacities of the basins.

\end{enumerate}

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\subsubsection{\R Hydrothermal Plume}

\begin{enumerate}

\item In spite of high temporal and spatial near-field variability, the
density-averaged particle plume was Gaussian in depth in 1997, without
indications for layering caused by the multiple sources. In 1998 the
plume was vertically bisected by a strongly sheared flow field
dispersing the hydrothermal tracers both NE- and SW-ward away from the
vent field.

\item In both years the particle plume was associated with cold/fresh
isopycnal hydrographic anomalies proportional to the light-scattering
signals. The 1997 near-field Gaussian mean plume was associated with
peak hydrographic anomalies of \degC*{-5}{-3} and \psu{-10^{-3}}; peak
anomalies in individual profiles were approximately six times higher.

\item The heat flux associated with the 1997 particle plume was
approximately \GW{2.5}. Height-of-rise modeling yields estimates which
are an order of magnitude smaller.

\end{enumerate}

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\subsection{Conclusions}

\subsubsection{Rift-Valley Hydrography and Flow}

\begin{enumerate}

\item The rift-valley flow in the \A segments is largely controlled by
topographic effects.

\item The persistence of the flow observed at \RS is consistent with
the low-pass filtering property of the basin/sill model; the inferred
characteristic filtering time scales of the \A segments are of order
weeks to months.

\item The along-segment hydrographic gradients and the rift-valley heat
budgets imply strong diapycnal mixing, consistent with the observed
dynamical processes; the diffusivity estimates appear high but not
impossible.

\item The known geothermal processes do not contribute significantly to
the heat budget of the rift-valley water in the \A segments.

\end{enumerate}

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\subsubsection{Hydrothermal Hydrographic Anomalies}

\begin{enumerate}

\item Hydrographic anomalies associated with hydrothermal particle
plumes can be detected and quantified even in locations of complex
hydrography where the water column overlying the plumes is not
characterized by simple $T/S$ relationships.

\item Hydrographic anomalies derived from properties extrapolated from
the water column above hydrothermal particle plumes can significantly
overestimate the anomalies associated with the plumes.

\end{enumerate}

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\subsubsection{\R Hydrothermal Plume}

\begin{enumerate}

\item The light-scattering signals in the near-field non-buoyant
hydrothermal plume behave conservatively, i.e.\ the particle
distribution near the vent field reflects varying hydrothermal effluent
concentrations.

\item Height-of-rise modeling significantly underestimates the buoyancy
and heat fluxes of the \R hydrothermal vent field, which consists of
multiple discrete sources distributed over an extended area.

\end{enumerate}
