%======================================================================
%                    C M / D I S C U . T E X 
%                    doc: Tue Mar 14 21:44:29 2000
%                    dlm: Wed Jun  7 23:07:49 2000
%                    (c) 2000 A.M. Thurnherr
%                    uE-Info: 36 53 NIL 0 0 72 3 2 4 ofnI
%======================================================================

The array of moored current meters provide a vast amount of information
on the variability of the flow in the vicinity of \RR on a range of
time scales spanning hours to months. While the overall patterns of the
hydrographic analysis are confirmed, the current meter data indicate
that the situation is far more complex than the gross hydrographic
patterns suggest. The main goal of the current meter data analysis in
the context of this thesis is the characterization of the low-frequency
variability and its influence on the advective transport of the
hydrothermal tracers away from the vent field. (Detailed analysis of
the high-frequency motions in our data set is outside the main focus of
the project  but there are many intriguing observations which merit
further investigation at a future stage.)

No dynamical signal unambiguously associated with the hydrothermal
buoyancy flux was observed in our data. The complexity of the spatial
and temporal patterns of the energetic motions in the rift valley
preclude the application of simple tests and the problem of detecting
plume signals appears even more difficult than on slow-spreading ridges
where hydrothermal plumes rise well above the topography but where
attempts at detecting dynamical signals associated with large plumes
have only recently been successful, requiring velocity profiles from a
moored ADCP \cite{GRL/joyce+98}. Within the rift valley of the \MAR the
problem is compounded by an apparent lack of theoretical, numerical and
laboratory investigations into the behavior of buoyancy sources on
steep slopes acting both as lateral and as bottom boundaries.

The estimates for the volume flux across \RS are intriguing because
they suggest that in spite of the flow variability on all observed
scales the along-valley transport below \m{2000} remained nearly
constant throughout the year. (Overflow currents showing little
variability over time scales of years have been observed elsewhere,
e.g.\ by an array of current meters deployed for two years in the East
Greenland Current downstream of Denmark Strait
\cite{Nature/dickson+90}.) The estimates for the transport across \RS
agree well with the hydraulic calculations of \rchapNP{HYD}. These
observations are used in \rchapNP{mixing} to derive mass and heat
budgets for the \A segments. If the quasi-steady view is correct,
implying that the transient warming event in the overlying water column
changed the flow patterns without strongly affecting the magnitude of
the along-valley transport, the question concerning the forcing of the
mean flow (c.f.\ \rsecNP{HYD-discu}) becomes even more important. In
\rchapNP{BOF} this question is addressed with a simple analytical and
numerical model.



