%======================================================================
%                    N E S P I / F L A M E . T E X 
%                    doc: Tue Aug 31 10:59:52 1999
%                    dlm: Wed Jun  7 23:38:49 2000
%                    (c) 1999 A.M. Thurnherr
%                    uE-Info: 117 23 NIL 0 0 72 3 2 4 ofnI
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% SCALED NEPHELS PROFILES

\begin{figure}[t]

\placeFig{NESPI/RFCoverlays}

\caption[1997 scaled nephelometry and spice profiles]{Overlays of
scaled nephelometry and spice profiles of the \F CTD data set;
successive profiles are horizontally offset by \protect\degC{0.03};
profiles \pa and \pb are the ones shown in \protect\rfigNP{Fmethod}.}

\labelFig{F-overlays}

\end{figure}

% SMALL-SCALE STRUCTURES WITHIN PARTICLE PLUME

\callout{\rFigNP{F-overlays}} shows a selection of the 1997 CTD
nephelometry profiles, scaled by the respective spice vs.\ nephel
regression slopes and overlaid on the corresponding spice profiles;
\pa and \pb are the ones shown in \rfigNP{Fmethod} while \pc and
\pd were selected for their vertically structured particle layers. The
agreement between the plume signatures of the corresponding profiles is
striking and indicates that the temperature and particle anomalies are
signatures of the same physical processes.

% PROFILES OUTSIDE PARTICLE PLUME

By definition the temperature anomalies outside the particle peaks are
zero \rsec{NESPI-bracket}. The extended profiles shown in
\rfigNP{F-overlays} allow some interesting observations, however.
Except in profile \pb between \m{2130} and \m{2350}, the anomalies
below the particle peaks remain close to zero, indicating that the new
methods estimate background $T/\rho$ properties consistent with the
water column below the hydrothermal equilibrium plume. Above the
particle peaks the slopes of the $T/\rho$ relationships are different,
resulting in the positive anomalies increasing upwards until
intersecting the interleaving structures which give rise to the large
negative spice anomalies at the top of the profiles. The temperature
anomalies are similarly biased towards the hydrography \emph{below} the
particle peaks in all profiles of the 1997 CTD data set, consistent
with the view that the equilibrium plume is a mixture of hydrothermal
effluents and fluid entrained during plume rise. Profile \pb
illustrates the effect of a non-linear $T/\rho$ relationship below the
particle peak (see also \rfigNP{Fmethod}) --- the positive anomalies
between \m{2130} and \m{2350} are of the same order of magnitude as the
negative anomalies associated with the particle layer, indicating that
it would not have been possible to establish the relevant background
from hydrographic data alone.  

% REGRESSION SLOPE PLOT

\begin{figure}[t]

\placeTwoFigs[0.6]{NESPI/RFCbilinvar}{NESPI/RFBbilinvar}

\caption[1997 spice vs.\ nephel regression coefficients]{Spice vs.\
nephel regression slopes (bilinear method) of the 1997 CTD and \BGT
data sets plotted against the corresponding horizontal distances from
the \R vent field; error bars show the 68.3\% confidence intervals;
shading of the symbols (different for the two data sets) is determined
by the correlation coefficients; the horizontal bands indicate the mean
($\pm1\sigma$) slopes. Profiles {\sffamily(a)---(d)} of the CTD data
set are those shown in \protect\rfigNP{F-overlays}; the two truncated
CTD profiles \protect\rsec{NESPI-bilin} are annotated with a \sfT. The
different symbols (squares and circles) of the \BGT data set indicate
profiles derived from the two separate but identical CTD instruments
\protect\rsec{F-methods}.}

\labelFig{bilinvar}

\end{figure}

% CTD VARIABILITY

In the left panel of \callout{\rfigNP{bilinvar}}, labeled ``(CTD)'',
the spice vs.\ nephel regression slopes from the \F CTD data set are
plotted against the corresponding horizontal distances from the vent
field. (In two of the profiles it was possible to calculate independent
values from separate particle peaks, resulting in the total of 15
estimates from 13 profiles.)

% BGT VARIABILITY

The \BGT hydrographic profiles are characterized by comparatively large
scatter in the conductivity measurements, contaminating the density
data. Out of the 24 \BGT profiles with nephelometry peak values
\V{>\!0.3} the bilinear method failed in 16 cases, either because no
correlation could be established (the limiting criterion $|r| \geq 0.4$
was chosen by inspection of the individual spice vs.\ nephel scatter
plots) or because the cross-correlation coefficients $r_{BC}$ fell
outside the range $[-0.8...0.2]$ \rsec{NESPI-bilin}. In the right panel
of \rfigNP{bilinvar}, labeled ``(BRIDGET)'', the remaining spice vs.\
nephel regression slopes are plotted against the corresponding
horizontal distances from the vent field.

% NO TRENDS

Other studies \citeEG{GRL/baker+95} indicate that correlations between
hydrothermal particle and temperature anomalies can vary with plume age
because of non-conservative particle behavior. No trends are apparent
in the \F data, possibly because of the short distances considered
here. Using the mean along-valley advection velocity at plume depth
(\mps{0.1}, from \rfigNP{meancur}) the 1997 profiles have nominal plume
ages \h{<\!17}. To a first approximation, the near-source spice vs.\
nephel regression slopes can therefore be considered constant with mean
values ($\pm1\sigma$) of \degCpV*{-1.9(\pm0.3)}{-2} (CTD) and
\degCpV*{-1.9(\pm0.5)}{-2} \BGTp{(}{).} \rFigNP{bilinvar} indicates
that the similarity of the two estimates is somewhat fortuitous, but it
is consistent with the similar response characteristics of the
different nephelometers used on the two platforms \rsec{F-methods}.

