Last updated: 2000.07.14



A.     Cruise Narrative:

A.1    Highlights

A.1.a  WOCE Line Designation:  AR10
       THE NORTH ATLANTIC TRACER RELEASE EXPERIMENT (NATRE):FINAL SAMPLING LEG


A.1.b  Expedition Designation: 74AB78_1
       (EXPOCODE) 

A.1.c  Chief scientists:       A. J. Watson
                               J. R. Ledwell
                               
A.1.d                          Ship: RRS CHARLES DARWIN CRUISE

A.1.e  Ports of call:          Ponta Delgada in the Azores to Lisbon

A.1.f  Cruise dates:           22/04/1993 - 24/05/1993
                               
Report prepared by: A. J. Watson, K. Van Scoy, J. R. Ledwell, C. S. Law,
D. Jones, C. Marquette, T. Donaghue, S. Watts, M. I. Liddicoat, C. Fernandez,
J. Bouthilette, D. Ciochetto, J. Donoghue, S. T. Bolmer,
K. Tedesco, K. Smith and J. Scott


A.2    Cruise Summary

We are pleased to acknowledge the assistance of the staff of the RRS Charles Darwin under
Captain R. Bourne. Their hard work and professional skills helped ensure that
this was a successful and enjoyable cruise.

Funding for NATRE is provided by the Natural Environment Research Council
in the UK and the National Science Foundation in the USA.


PERSONNEL LIST

R. A. Bourne     Master
C. M. Leather    C/O
P. Newton        2/O
R. A. Warner     2/O
J. G. Baker      R/O
I. R. Bennet     C/E
D. E. Anderson   2/E
V. E. Lovell     3/E
S. F. Dean       3/E
M. Trevaskis     CPO
T. G. Lewis      PO
A. Marren        SG. 1A
S. Jones         SG. 1A
K. R. Luckhurst  SG. 1A
J. Miller        SG. 1B
C. Hubbard       S.C.M
K. Peters        COOK
R. Edes          STWD
A. P. Lee        STWD
J. P. Taylor     STWD
I. M. Slater     MM. 1A
A. J. Watson     Chief Scientist
C. S. Law        Scientist
M. I. Liddicoat  Scientist
K. Van Scoy      Scientist
S. T. Bolmer     Scientist
J. Bouthilette   Scientist
J. Donoghue      Scientist
T. Donoghue      Scientist
C. Fernandez     Scientist
C. Marquette     Scientist
K. Tedesco       Scientist
D. Ciochetto     Scientist
J. Scott         Scientist
W. K. Smith      Scientist
D. A. Jones      Scientist
S. F. Watts      Scientist
J. R. Ledwell    Scientist


INTRODUCTION AND CRUISE OBJECTIVES

This cruise was the third and last scheduled "tracer documentation" cruise 
associated with the North Atlantic Tracer Release Experiment (NATRE). The 
experiment is a major international exercise under the auspices of the World Ocean 
Circulation Experiment, "Core 3" programme, in which UK, US and Canadian 
scientists and ships are participating. Its object is to study the rates of both vertical 
and horizontal mixing in the main pycnocline of the Northeast Atlantic subtropical gyre, 
using a release of sulphur hexafluoride (SF6) tracer, marked by neutrally buoyant 
floats, and accompanied by an extensive suite of measurements of micro- and fine-
structure of the kind more conventionally used to infer rates of vertical mixing. By these 
means the existing techniques will be validated against a direct and accurate 
measurement of mixing processes associated with the tracer experiment. The 
experiment was initiated in April/May 1992 in a two-ship exercise in which the Woods 
Hole vessel R/V Oceanus released 139kg of tracer and the neutrally buoyant floats, 
while the Charles Darwin documented the distribution of the tracer in the first month 
after release (Cruise CD68). Subsequently, at six months after release, the Oceanus 
returned to the area and documented the distribution of about 25-33% of the tracer 
during October and November 1992, finding two lengthy streaks extending to about 
600km in length and typically 3km wide by 18m thick. An accurate measure of the 
vertical mixing rate during the April-October period was obtained by comparison of the 
CD68 data with these Oceanus observations.

The task of the present cruise was to document the distribution of the tracer one year 
after release. In this we were assisted by the Canadian research vessel CSS 
Hudson, currently in the area conducting microstructure measurements as part of the 
overall experiment. Dr. James Ledwell, the Principal Scientist on the US component of 
the experiments, was aboard the Hudson and made some tracer measurements in 
advance of our cruise, so that we had information on the location of at least some of 
the tracer before we left port.


NARRATIVE

Figure 1 shows the overall cruise track, from Ponta Delgada in the Azores to Lisbon. 
We sailed from Ponta Delgada at 0810 on 22nd April 1993, and made course 204°T for 
a previously agreed rendezvous with the CSS Hudson, at 26° 50'N, 31° 20'W. Hudson 
had to make an unscheduled journey to Las Palmas, due to a medical emergency, 
which set back their programme considerably. The original reason for the early 
rendezvous was to transfer analytical equipment to speed sample analysis. Dr. 
James Ledwell, at this time aboard the Hudson, was scheduled to transfer to Darwin 
but not before about 10th May when the Hudson would leave the NATRE site.

We kept a regular radio schedule with the Hudson throughout the period that the two 
ships were working. We were told that they had succeeded in locating some of the 
neutrally buoyant SOFAR floats originally released with the tracer, i.e. float 55 at 23° 
50'N, 30° 20'W, and float 58 at 21° 20'N, 30° 30'W, in what might be the SE corner of 
the tracer patch. One float, to which was attached a "Richardson Number" (RiNo) 
neutrally buoyant float, appeared at that time to be at about 30°N, 37°W, in what might 
demarcate a NW corner. This position later proved to be incorrect, but nevertheless 
the assumption that the tracer lay mostly east and south of there was verified.

We arrived at the rendezvous in the early hours of 25th April, but continued past the 
Hudson, having elected to postpone transfer of equipment for a time. After crossing 
29°N, we began exploratory casts through the target surface, spacing these 
approximately 50 miles apart. No tracer was found on the first three casts, but we 
encountered it on the fourth, which was at the original rendezvous point.

It was soon apparent that the tracer had spread into an enormous area of ocean: the 
concentrations we observed averaged about 25fM, with column integrals averaging 
around 2 x 10-9 moles/m2, and given the initial amount released of approximately 1000 
moles this indicates a patch ~700km on a side. However the shape was not regular 
or simple, and the concentration varied widely even on the 10-20km scale. Given that 
we had very little information at the beginning of the cruise as to where this patch 
might be centred or what its shape might be, it was thought that it would not be 
possible to comprehensively document the entire patch. Instead we aimed to get a 
sufficient number of profiles, from many different areas of the patch, to be confident of 
a statistically valid description of properties such as the vertical thickness and 
streakiness. In the event however, we did end by accounting for more than 90% of the 
tracer.

Having approached the region on a course of 204°T we saw no reason to deviate after 
passing the Hudson, so continued on this heading for the better part of a week, finally 
running out of the patch at 21° 20'N latitude. We then executed a series of east-west 
sections spaced approximately 1 apart in latitude, heading northwards, (see cruise 
track for the working area, Figure 2). This pattern was designed to be complemented 
by the tracer measurements performed from the Hudson (see Figure 29 for a map of 
Hudson stations). The pattern was broken at about the time of our RiNo hunt (see 
below), to make a number of tows using a high-resolution sampling system, and 
towards the end of the cruise when we "filled in" corners in the north-west and south-
east. We finished science at 1200 on 19th May and set course for Lisbon, docking 
there at 1700 on 24th May.

Sampling Casts

These were to 500m: on the downcast, the depth of the target isopycnal (actually at 
sigma 0.3 = 28.050, though we used the previous year's calibration of the BBC 
microcomputer which gave sigma 0.3 = 28.0395), was noted - it was generally 
between 300 and 400m depth. On the upcast, bottles were triggered at 10m intervals, 
starting 120m below the depth of the target surface and ending 120m above it. We 
found that the time taken for each cast was roughly an hour, which meant that at a 
spacing of 10 miles or more between casts, the limiting factor on the rate at which we 
could proceed was not the rate of processing samples in the laboratory, but the wire 
time and steam time. Stations were spaced initially at 10 mile intervals, but the 
"standard" spacing was increased to 15 miles after station 22 (Table 1). Stations 
were grouped into geographical working areas (Figure 3). Tracer and salt samples 
only were taken from the Niskin bottles, and the work continued 24 hours a day. We 
found that we could progress about 130 miles per day in this mode, with the ship on 
station and wire out for about half the time, and steaming at 10kt the other half of the 
time.

Rendezvous with CSS Hudson

On 6th May we broke off sampling to rendezvous with the Hudson, chiefly for the 
purpose of transferring Dr. Ledwell from the Hudson to the Darwin. Hudson at this 
time was continuing her programme of CTD and "Epsonde" microstructure casts for 
the overall experiment under the direction of Chief Scientist Neil Oakey of Bedford 
Institute of Oceanography. The rendezvous was at 1000, at 24° 58'N, 31° 6'W. The 
Master of the Hudson invited members of the Darwin's company over for lunch which 
was taken up by nine scientists and ships personnel including the PSO. We extended 
a reciprocal invitation, which was taken up by Dr. Oakey and several members of the 
science party aboard Hudson. Gifts were exchanged between the two ships 
companies. Dr. Ledwell transferred, and we took the opportunity to transfer a SF6 gas 
standard from the Hudson to the Darwin to cross calibrate our measurements with 
theirs. We were finished with the transfer and pleasantries at about 1430 and 
departed to continue our programme.

Hunt for the RiNo

One of the aims of Hudson was to locate and recover the Richardson Number (RiNo) 
float deployed by Oceanus at the time of the tracer injection. RiNo is tracked by SOFAR 
signal, and at close range by means of a 10kHz beacon. We determined last year 
during cruise CD68 that the Simrad EA500 precision echo-sounder aboard the 
Darwin was an efficient instrument for sensing these beacons.

The task of recovering the RiNo was greatly hampered by what appears to have been 
a malfunction of the clock on the SOFAR beacon, which initially led the team aboard 
the Hudson to believe that the float was situated well to the west at about 36°W. 
Latterly, the best guess for the position of the float was thought to be near 26° 15'N, 
29° 30'W. We offered to assist the Hudson in the search they were to undertake for 
this float after leaving our rendezvous, since the Simrad was thought to have a better 
range for the 10kHz beacon than the equipment aboard the Hudson. We agreed to 
search two lines out of a grid of 5 lines, covering a region about 8-18 miles NW of the 
most likely position of the float.

The search began at 1600 on 7th May and lasted until about 1300 the following day. 
The actual lines originally agreed with Hudson took only 8 hours. These are shown in 
Figure 4. However, as we were ending this pattern we saw a trace on the Simrad, 
lasting about 20 minutes, which looked characteristic of a beacon behind the ship. 
The trace was very faint, appearing and then disappearing without obvious cause. We 
therefore re-traced and re-retraced our course, running over the section on which the 
signal had appeared a total of four times, but without seeing it again. We then began 
a box-search pattern (Figure 5) centred on the location where we considered the 
source most likely to be, and continued this for 8 hours further, without at any time 
again seeing the signal. We remain unsure about the source of this signal, but we 
know of no phenomenon other than a regularly repeating beacon which could give 
rise to such a trace. Therefore we believe that we must have heard the float we were 
searching for, but perhaps due to freak acoustic conditions, at a distance very much 
greater than the normal range of the apparatus.

Sled Tows using High-Resolution Carousel Sampler

Casts 220 through 223 were tows in which the CTD was mounted on a sled with 
sequentially filling syringe samplers. 50 samples were collected on each tow, but the 
distance covered varied from 8 to 65km (Table 2). The package was lowered on the 
CTD wire from the starboard "A" frame, and "flown" on the target surface by automated 
control of the winch, using the control system developed by R. Powell of RVS for 
cruise CD68. The longest tow entailed steaming at approximately 2kt, at which speed 
the wire angle was considerable (60-70° from the vertical). The tracks towed along 
are shown in Figure 6 and the along-track concentrations are shown in Figure 7: they 
reveal a pattern of "plates" of relatively constant concentrations of dimension ~10km, 
separated by rather sharp boundaries.


CTD DATA

Calibration

Hydrographic data were gathered with an EG&G MkIII CTD, equipped with PRT 
thermometers and a single conductivity probe. A laboratory temperature calibration 
performed just rpior to the cruise indicated that the primary PRT was within 0.0005°C 
of the bath standard. No adjustment was made for a temperature offset.

Salinity samples taken on each cast showed the salinity reading from the system to 
be low by 0.028-0.029psu throughout the cruise. The constants in the acquisition 
system had already been set to compensate for a raw salinity that was low by 
0.018psu. Thus, another 0.011psu were added to the salinity calculated using these 
constants.

The pressure sensor read high by 4.7db at the surface, and this amount was 
subtracted from all pressures throughout the cruise.

A sample profile and a theta/S plot are shown in Figures 8 and 10, respectively.

Data Reduction

The descent for each cast was selected from the CTD data stream, and made into a 
separate file named "cd780xxx.dat", where "xxx" represents the number of the cast, 
from 001 to 241. These raw data were then interpolated to a 1db pressure grid and 
stored in files called "cd780xxxpi.dat". At the same time the potential temperature theta0.3, 
and potential density sigma 0.3, both referenced to 300db, were added to the files, in 
the 4th and 5th columns, respectively. A sixth column reports the number of scans 
skipped during the original file because the pressure was decreasing. Seldom was 
this number different from 0, since the weather was light, and the payout rate of the 
CTD wire was typically 60m/min.

The target sigma 0.3 for the tracer release was 28.05kg/m3. Hydrographic properties 
at this surface were estimated from the CTD data for each cast (Table 3), and vertical 
gradients in the properties were estimated for casts that went more than 50m below 
the target surface, as follows.

First, the nearest pressure to the target density surface was found, and a window 
spanning ±50db about this pressure was selected. A quadratic fit of theta0.3 versus 
sigma 0.3 in this window was performed, and the value of theta0.3 at the target surface 
was determined from the resulting polynomial. This procedure reduces the 
uncertainty in finding the target surface created by noise in salinity which propagates 
to potential density. The salinity at the target density was then found from the potential 
temperature, using the equation of state. Also, an accurate pressure at the target 
surface was found by interpolation.

Gradients of in situ temperature, dT/dP, and salinity, dS/dP, at the target surface were 
then determined by making quadratic fits of T(P) and S(P) in the ±50db window about 
the target surface. The coefficient of thermal expansion, alpha, the change of density 
with salinity, beta, and the adiabatic lapse rate, gamma, were determined at the target 
surface. Then, a density gradient, dsigma/dp, the density ratio, R-rho, and the 
buoyancy frequency, N, were calculated from the following equations:

Rho-0 = 1000 + sigma0		rho = 1000 + sigma3

d-sigma/dP = rho-0 [alpha { -dT/dP + gamma } + beta dS/dP ]

R-rho = alpha { -dT/dP + gamma } / { -beta dS/dP }

N = sqrt { g (d-sigma/dP) / rho }

The values for P, theta0.3, S, -dT/dP, -dS/dP, d-sigma/dP, R-rho, and N at the target density 
surface are given for each cast in Table 4.

The CTD casts were sorted into the same groups as the tracer data (Table 5). The 
data from each group were averaged, and the average data were treated the same 
way as above to give the properties and gradients for each group (Table 4).

The last entry in Table 4 gives the properties and gradients calculated from the 
average of the deep CTD profiles that went at least 50db deeper than the target 
surface for the whole cruise. This average CTD profile is tabulated every 10db in 
Table 3, and is plotted in Figure 9. A typical theta/S relation is plotted in Figure 10 and the 
mean theta/S relation is plotted in Figure 11.


SF6 DATA

SF6 Analysis

Water samples were analysed using two identical systems (A and B), each of which 
consisted of a vacuum-sparge front end in which the SF6 was stripped from the water 
and trapped on Porapak Q at -70°C, followed by chromatographic separation and 
detection by an Electron Capture Detector (Shimadzu GC8-AIE). Both systems were 
fully automated requiring minimal input from the operator, and so reducing any errors 
arising from sample handling and manual valve-switching. Water from the Niskin 
bottles were sub-sampled into 500ml glass bottles which were flushed three times, 
and then transferred to the laboratory where they were stored underwater. The SF6 
concentration at the target density was obtained within 10 minutes of the CTD landing 
on deck, allowing alterations in the cruise track to be made relatively rapidly. A volume 
of 350ml was required for analysis of profile samples, although GC-B was adjusted to 
facilitate analysis of 50ml samples obtained from the carousel sampler for a period of 
4 days towards the end of the cruise. A typical profile cast consisted of 25 samples, 
which at a rate of 6.75 minutes per sample resulted in a cast analysis time of 90 
minutes; in total, 5000 water samples and 500 standards were run by a pool of 10 
analysts.

The sensitivity of GC-A and B were 0.05 and 0.03fmol/l, respectively, although the 
background concentration was higher than these values. Samples from each profile 
were artificially divided, with the "tails" of the profile analysed on the more sensitive 
GC, and the middle of the profile on the less sensitive system. Duplicate samples 
from the target density were run on both instruments at the start of each cast analysis 
to determine an average reproducibility of 3.6% between the two instruments. This 
reproducibility is a reflection of the difference in calibration between the two 
instruments as opposed to variability in the efficiency of the analysis. The 
reproducibility within both GC's was 0.6% (A) and 0.88% (B) for duplicate samples 
(including background samples).

Calibration of each system took approximately 75 minutes every 36-48 hours, 
requiring certain casts to be run entirely on one system while the other was calibrated. 
The response of both instruments remained relatively constant (Table 6), except for 
the initial recovery of GC-A in the first 3 days from a previous contamination event on a 
recent cruise. Despite continuous analysis for 30 days, both instruments performed 
extremely well with virtually no down-time and minimal sample back-up. A valve driver 
board had to be replaced at the start of the cruise when a motor burnt out during start 
up on GC-A, and occasional maintenance was required to clean up salt crystal 
deposit in valves and solenoids on both systems. The gland in the 29.4ppt standard 
cylinder failed, although the calibration fitting programme was able to compensate for 
the absence of standards in this range.

SF6 Data Reduction

The SF6 data were calibrated using a linear fit for samples less than 1.3 x 10-14 moles 
(300ppt in 1ml gas standard), smoothly joined to a cubic fit for higher values: previous 
work at PML has shown this to be the best polynomial type of fit to cover the range 0 to 
5 x 10-13 moles. Calibrated data, identified by Niskin bottle number, were merged on 
the RVS computer with CTD data from the last frame before the bottle was closed. For 
each cast, a file was made tabulating pressure, temperature, salinity, sigma 0.3, and 
SF6 for each bottle. These files constitute a basic data output from the cruise.

For further analysis, the SF6 profiles were interpolated onto a regular density grid (27.8 
to 28.2 x 0.01) and averaged by regional group (Figure 3) to give statistics on mean 
concentration, depth and rms width. To obtain meaningful widths in depth (actually 
pressure) space, correctly referenced to the target surface, the mean pressure versus 
density profile of the initial sampling cruise CD68 was used to map SF6 from density 
space into pressure. Individual profiles versus sigma 0.3, these mean profiles versus 
"CD68" depth, and the statistics of mean depth and rms width relative to the centre of 
mass are plotted in Figures 12-24. The interpolation could profitably have been 
continued to 28.3 as data from the lower tail were sometimes missed out of the 
interpolation.

The entire cruise average of casts interpolated from 27.8 to 28.3 is plotted in Figure 
26. The centre of mass is at 28.058, 0.008 units lower than the original injection, and 
the rms width relative to the centre of mass is 31.14m in "CD68" depth space. The 
width indicates a vertical mixing rate, Kz in the range 0.17 to 0.2cm2/s since the 
October-November period when the tracer was last sampled. This is significantly 
larger than the value of 0.11cm2/s for the first 6 months of the experiment, presumably 
due to larger forcing energy during the winter months. The actual value of Kz will be 
defined to better accuracy after post-cruise analysis. The average profile is almost a 
perfect gaussian (see Figure 27).

The lateral dispersion of the tracer, expressed as column integral in nmol/m2, is 
shown in Figure 30 after gridding and contouring the data, using a 0.75 degree radius 
of integration. The tracer was spread over about 5-6 degrees of latitude and 9-10 
degrees of longitude - an area in excess of 150000 square miles. Though still highly 
variable in space, there were few points within this region that had no tracer at all - in 
other words, the tracer streaks had combined to "paint in" this area. Integrating under 
the contours gives a total amount of 937 moles, which is less than 2% different from 
the 950 moles which were released. Ana alternative way of integrating the tracer, by 
obtaining an average concentration along the cruise track and multiplying by the 
overall area covered, gave essentially the same value. However, the margin of error is 
undoubtedly larger than these figures suggest. Provisionally we estimate that we 
accounted for 99±10%.

TABLE 1: STATION LIST

Notes:
1) "Full" casts were 24 bottle casts with approx 10m spacing centred on the target surface.
2) "Short" casts: one or two bottles were fired at the target surface only.
3) "Background" casts (2-4) were used as representative background measurements, 
   the average of which was subtracted from the remainder in all calculations.
4) "Sled" casts (218-223) were tows along the target surface of the WHOI sled with 
   carousel samplers.
5) The SF6 column integral, background subtracted, is in nanomoles per square 
   metre. "est" indicates it was estimated from the concentration at the target surface.
6) Casts 38-65 are numbered differently in the original cast sheets: original 
   numbering is in brackets under "cast type".


Cast Date       Time GMT  Latitude    Longitude   Cast type    SF6 Column 
                                                               Integral
-------------------------------------------------------------------------
1    22/04/93   19:23     35 55.76N   26 38.05W   background   0.00     
2    24/04/93   13:36     29 0.32N    30 14.82W   background   0.00     
3    24/04/93   19:14     28 17.12N   30 36.97W   background   0.00     
4    25/04/93   00:44     27 33.24N   30 58.01W   background   0.00     
5    25/04/93   06:26     26 49.86N   31 20.12W   full         2.69     
6    25/04/93   09:27     26 32.01N   31 27.75W   full         3.92     
7    25/04/93   11:49     26 22.21N   31 32.92W   full         2.04     
8    25/04/93   14:00     26 13.14N   31 37.98W   full         1.28     
9    25/04/93   16:00     26 4.20N    31 42.89W   full         0.86     
10   25/04/93   18:16     25 54.99N   31 47.06W   full         1.72     
11   25/04/93   20:42     25 45.90N   31 51.47W   full         2.01     
12   25/04/93   23:00     25 35.82N   31 56.38W   full         2.75     
13   26/04/93   01:02     25 26.93N   32 0.83W    full         1.19     
14   26/04/93   03:07     25 18.23N   32 4.88W    full         1.50     
15   26/04/93   05:31     25 8.85N    32 9.92W    full         0.52     
16   26/04/93   08:02     24 59.63N   32 14.25W   full         2.59     
17   26/04/93   10:48     24 50.34N   32 18.02W   full         6.03     
18   26/04/93   13:04     24 41.23N   32 22.68W   full         4.42     
19   26/04/93   15:25     24 32.11N   32 27.71W   full         6.23     
20   26/04/93   17:39     24 23.11N   32 32.14W   full         2.86     
21   26/04/93   19:52     24 13.65N   32 36.36W   full         0.59     
22   26/04/93   22:22     24 4.95N    32 40.88W   full         0.87     
23   27/04/93   01:03     23 50.89N   32 47.14W   full         1.06     
24   27/04/93   03:41     23 37.28N   32 53.94W   full         0.39     
25   27/04/93   06:24     23 23.11N   32 59.93W   full         2.74     
26   27/04/93   09:08     23 9.27N    33 6.79W    full         3.12     
27   27/04/93   11:55     22 55.06N   33 13.27W   full         0.76     
28   27/04/93   14:32     22 41.09N   33 19.71W   full         1.22     
29   27/04/93   17:05     22 28.21N   33 25.99W   full         1.89     
30   27/04/93   19:50     22 14.43N   33 32.51W   full         2.76     
31   27/04/93   22:30     22 0.48N    33 39.01W   full         0.82     
32   28/04/93   01:08     21 46.66N   33 45.25W   full         0.40     
33   28/04/93   04:15     21 32.12N   33 51.87W   full         0.05     
34   28/04/93   06:53     21 19.02N   33 58.91W   short        0.00     
35   28/04/93   10:43     21 19.29N   33 26.90W   short        0.00     
36   28/04/93   14:09     21 18.94N   32 54.44W   short        0.00     
37   28/04/93   17:40     21 19.02N   32 22.36W   short        ?     
38   28/04/93   18:18     21 19.47N   32 22.33W   full (37i)   0.39     
39   28/04/93   22:04     21 18.96N   31 50.27W   short (38)   ?     
40   28/04/93   22:42     21 19.15N   31 50.21W   full (38i)   0.31     
41   29/04/93   01:48     21 42.17N   31 49.96W   full (39)    0.42     
42   29/04/93   05:04     22 6.08N    31 50.24W   full (40)    0.08     
43   29/04/93   08:23     22 29.97N   31 50.41W   full (41)    0.49     
44   29/04/93   10:46     22 29.94N   32 4.29W    full (42)    0.45     
45   29/04/93   13:17     22 30.19N   32 20.10W   full (43)    0.82     
46   29/04/93   15:53     22 29.95N   32 36.18W   full (44)    0.87     
47   29/04/93   18:30     22 29.98N   32 52.04W   full (45)    0.36     
48   29/04/93   21:24     22 30.00N   33 7.87W    full (46)    0.91     
49   30/04/93   01:17     22 30.15N   33 40.17W   full (47)    1.58     
50   30/04/93   04:17     22 29.55N   33 55.96W   full (48)    0.92     
51   30/04/93   07:07     22 29.61N   34 11.94W   full (49)    0.32     
52   30/04/93   09:47     22 29.77N   34 28.17W   full (50)    0.20     
53   30/04/93   12:18     22 29.94N   34 43.96W   full (51)    0.26     
54   30/04/93   14:36     22 29.53N   34 59.84W   full (52)    0.16     
55   30/04/93   17:00     22 29.87N   35 16.20W   full (53)    0.00     
56   30/04/93   19:50     22 44.97N   35 16.10W   full (54)    0.12     
57   30/04/93   22:26     22 59.98N   35 16.04W   full (55)    0.02     
58   1/05/93    01:01     23 15.37N   35 16.06W   full (56)    0.00     
59   1/05/93    03:24     23 30.32N   35 16.25W   full (57)    0.84     
60   1/05/93    06:02     23 29.87N   34 59.76W   full (58)    0.09     
61   1/05/93    08:35     23 30.05N   34 44.04W   full (59)    0.00     
62   1/05/93    12:37     23 30.23N   34 12.37W   full (60)    0.08     
63   1/05/93    15:00     23 30.11N   33 55.54W   short (61)   0.00     
64   1/05/93    16:58     23 30.12N   33 39.35W   short (62)   0.00     
65   1/05/93    17:29     23 30.46N   33 39.37W   full (63)     0.45     
100  1/05/93    19:49     23 30.13N   33 23.00W   full          0.02     
101  1/05/93    22:21     23 29.87N   33 7.04W    full          2.75     
102  2/05/93    00:57     23 30.15N   32 50.57W   full          0.46     
103  2/05/93    03:16     23 37.53N   32 58.18W   full          3.58     
104  2/05/93    05:27     23 45.03N   32 58.64W   full          1.35     
105  2/05/93    07:29     23 44.93N   33 6.78W    full          2.77     
106  2/05/93    09:56     23 37.29N   33 15.21W   full          0.79     
107  2/05/93    11:42     23 37.57N   33 6.84W    full          3.34     
108  2/05/93    15:09     23 37.60N   32 39.58W   full          0.65     
109  2/05/93    18:07     23 30.14N   32 24.00W   full          3.15     
110  2/05/93    20:48     23 29.98N   32 8.16W    full          2.53     
111  3/05/93    01:32     23 30.48N   31 51.76W   full          2.35     
112  3/05/93    04:38     23 30.15N   31 35.33W   full          0.93     
113  3/05/93    07:15     23 29.91N   31 19.21W   full          3.67     
114  3/05/93    09:51     23 30.13N   31 3.01W    full          1.27     
115  3/05/93    12:25     23 30.28N   30 46.78W   full          1.33     
116  3/05/93    16:37     23 30.02N   30 30.26W   full          4.14     
117  3/05/93    19:21     23 30.13N   30 14.22W   full          1.05     
118  3/05/93    22:12     23 29.90N   29 58.16W   full          3.39     
119  4/05/93    00:47     23 30.31N   29 41.69W   full          0.48     
120  4/05/93    03:46     23 30.26N   29 25.19W   full          0.18     
121  4/05/93    06:32     23 29.94N   29 8.74W    full          0.23     
122  4/05/93    09:08     23 30.13N   28 52.45W   full          0.00     
123  4/05/93    11:53     23 30.22N   28 36.17W   full          0.14     
124  4/05/93    14:28     23 30.18N   28 19.51W   full          0.45     
125  4/05/93    16:59     23 30.15N   28 3.37W    full          0.28     
126  4/05/93    19:36     23 45.04N   27 59.84W   full          0.35     
127  4/05/93    22:28     23 59.94N   27 59.82W   full          0.27     
128  5/05/93    02:52     24 29.94N   27 59.99W   full          0.32     
129  5/05/93    06:03     24 29.92N   28 16.51W   full          0.41     
130  5/05/93    08:31     24 30.23N   28 32.88W   full          1.85     
131  5/05/93    10:40     24 30.12N   28 43.86W   full          3.30     
132  5/05/93    12:50     24 30.12N   28 54.91W   full          3.55     
133  5/05/93    15:22     24 30.35N   29 11.29W   full          1.79     
134  5/05/93    18:16     24 30.02N   29 27.76W   full          2.02     
135  5/05/93    20:44     24 29.89N   29 44.46W   full          8.70     
136  5/05/93    23:10     24 29.87N   30 0.42W    full          0.49     
137  6/05/93    01:37     24 29.82N   30 17.06W   full          4.34     
138  6/05/93    04:05     24 30.18N   30 33.54W   full          3.87     
139  6/05/93    06:15     24 29.87N   30 50.15W   full          2.01     
140  6/05/93    16:19     24 44.97N   31 6.41W    full          1.22     
141  6/05/93    18:47     24 30.04N   31 6.60W    full          3.59     
142  6/05/93    21:44     24 45.02N   30 50.01W   full          1.28     
143  7/05/93    00:14     24 58.27N   30 43.64W   full          1.00     
144  7/05/93    02:40     25 12.62N   30 36.85W   full          0.72     
145  7/05/93    04:54     25 26.47N   30 29.98W   full          0.39     
146  7/05/93    07:12     25 39.96N   30 23.01W   full          3.46     
147  7/05/93    09:30     25 53.79N   30 16.13W   full          0.09     
148  7/05/93    11:52     26 7.81N    30 9.63W    full          0.00     
149  7/05/93    14:11     26 7.89N    29 53.16W   full          0.18     
150  7/05/93    17:44     26 21.70N   29 35.85W   short               
151  8/05/93    09:54     26 22.09N   29 35.00W   full          0.16     
152  8/05/93    12:52     26 22.45N   29 52.44W   full          0.05     
153  8/05/93    15:12     26 22.27N   30 9.20W    full          0.00     
154  8/05/93    17:37     26 22.20N   30 26.05W   full          0.04     
155  8/05/93    20:15     26 22.08N   30 46.86W   full          0.12     
156  8/05/93    22:37     26 8.94N    30 53.88W   full          0.00     
157  9/05/93    00:53     25 54.57N   31 0.29W    full          0.01     
158  9/05/93    03:12     25 41.18N   31 7.24W    full          0.00     
159  9/05/93    05:27     25 27.04N   31 14.19W   full          1.22     
160  9/05/93    07:35     25 13.08N   31 20.52W   full          3.44     
161  9/05/93    10:14     24 59.22N   31 27.05W   full          2.08     
162  9/05/93    12:26     24 45.92N   31 34.06W   full          5.14     
163  9/05/93    18:09     24 29.95N   31 41.57W   full          4.51     
164  9/05/93    20:39     24 29.94N   31 57.76W   full          2.91     
165  9/05/93    23:06     24 30.19N   32 14.39W   full          1.55     
166  10/05/93   01:26     24 30.02N   32 30.90W   full          0.60     
167  10/05/93   03:45     24 29.86N   32 47.17W   full          4.57     
168  10/05/93   05:50     24 29.91N   32 58.05W   full          4.48     
169  10/05/93   07:48     24 29.88N   33 9.10W    full          4.57     
170  10/05/93   09:44     24 30.10N   33 19.79W   full          5.58     
171  10/05/93   11:40     24 30.07N   33 30.76W   full          5.02     
172  10/05/93   13:41     24 30.07N   33 41.89W   full          5.01     
173  10/05/93   15:37     24 30.22N   33 52.90W   full          5.13     
174  10/05/93   17:40     24 30.26N   34 4.20W    full          3.99     
175  10/05/93   19:32     24 30.18N   34 15.10W   full          5.86     
176  10/05/93   21:35     24 29.95N   34 26.12W   full          4.27     
177  10/05/93   23:23     24 29.97N   34 37.15W   full          5.80     
178  11/05/93   01:13     24 30.07N   34 47.81W   full          3.18     
179  11/05/93   03:04     24 30.22N   34 58.95W   full          0.81     
180  11/05/93   05:33     24 30.13N   35 15.35W   full          0.08     
181  11/05/93   07:51     24 30.15N   35 31.96W   full          0.82     
182  11/05/93   10:12     24 29.70N   35 48.40W   full          3.02     
183  11/05/93   12:25     24 29.81N   36 4.34W    full          0.65     
184  11/05/93   14:51     24 29.66N   36 20.84W   full          1.23     
185  11/05/93   17:01     24 29.79N   36 37.34W   full          0.79     
186  11/05/93   19:14     24 29.93N   36 53.64W   full          0.03     est.
187  11/05/93   21:29     24 29.84N   37 10.30W   full          0.15     
188  11/05/93   23:55     24 44.42N   37 10.58W   full          0.08     est.
189  12/05/93   02:41     24 59.21N   36 54.85W   full          0.21     
190  12/05/93   05:10     25 14.43N   36 53.99W   full          0.11     
191  12/05/93   08:15     25 29.73N   36 38.03W   full          0.34     
192  12/05/93   10:40     25 44.79N   36 37.70W   full          0.28     
193  12/05/93   13:33     25 59.73N   36 37.64W   full          1.93     
194  12/05/93   16:06     26 15.06N   36 37.91W   full          1.98     
195  12/05/93   18:33     26 29.69N   36 37.57W   full          1.35     
196  12/05/93   21:05     26 44.87N   36 37.67W   full          0.01     
197  12/05/93   23:33     27 0.01N    36 37.79W   full          0.00     
198  13/05/93   02:44     27 15.18N   36 20.85W   full          0.05     
199  13/05/93   05:46     27 29.86N   36 4.58W    full          5.34     
200  13/05/93   08:24     27 40.58N   35 51.54W   full          0.84     
201  13/05/93   10:59     27 40.90N   35 34.65W   full          1.27     
202  13/05/93   13:09     27 40.90N   35 17.97W   full          0.57     
203  13/05/93   15:28     27 40.87N   35 0.17W    full          0.64     
204  13/05/93   17:49     27 40.65N   34 42.33W   full          0.35     
205  13/05/93   20:10     27 25.86N   34 37.53W   full          1.70     
206  13/05/93   22:18     27 12.58N   34 33.90W   full          0.82     
207  14/05/93   00:23     27 0.10N    34 30.00W   full          1.59     
208  14/05/93   02:42     26 45.05N   34 29.84W   full          0.81     
209  14/05/93   04:56     26 30.18N   34 30.03W   full          0.61     
210  14/05/93   07:06     26 29.82N   34 46.78W   full          0.47     
211  14/05/93   09:16     26 30.18N   35 3.49W    full          1.42     
212  14/05/93   11:31     26 30.25N   35 20.35W   full          0.36     
213  14/05/93   13:45     26 30.00N   35 35.99W   full          1.72     
214  14/05/93   17:12     26 0.16N    35 36.96W   full          3.57     
215  14/05/93   19:28     25 45.11N   35 36.88W   full          5.07     
216  14/05/93   21:46     25 30.09N   35 36.97W   full          2.13     
217  15/05/93   01:22     25 7.46N    35 15.12W   full          1.29     
218  15/05/93   08:00     24 15.07N   34 24.98W   sled (test)         
219  15/05/93   09:15     24 14.62N   34 24.78W   sled (aborted)          
220  15/05/93   10:50     24 15.89N   34 24.65W   sled tow            
221  15/05/93   16:00     24 19.73N   34 24.60W   sled tow            
222  16/05/93   02:51     24 53.49N   34 22.51W   sled tow            
223  16/05/93   21:10     23 37.08N   32 39.92W   sled tow            
224  17/05/93   22:28     22 31.87N   31 16.76W   full          1.38     
225  18/05/93   00:44     22 27.30N   31 2.35W    full          0.84     
226  18/05/93   03:00     22 21.79N   30 46.99W   full          1.07     
227  18/05/93   05:13     22 16.28N   30 31.72W   full          0.81     
228  18/05/93   07:21     22 1.42N    0 31.76W    full          0.88     
229  18/05/93   09:37     21 46.39N   30 31.61W   full          1.12     
230  18/05/93   11:49     21 31.90N   30 31.26W   full          0.37     
231  18/05/93   13:54     21 20.62N   30 31.87W   full          0.00     
232  18/05/93   16:08     21 31.29N   30 21.39W   full          0.00     
233  18/05/93   18:15     21 41.67N   30 9.95W    full          0.00     
234  18/05/93   20:39     21 52.09N   29 58.33W   full          0.00     
235  18/05/93   22:49     22 1.94N    29 46.81W   short         0.00     
236  19/05/93   00:46     22 12.61N   29 36.14W   short         0.00     
237  19/05/93   02:41     22 23.16N   29 24.42W   short         0.00     
238  19/05/93   04:40     22 34.12N   29 12.82W   short         0.05     est.
239  19/05/93   06:35     22 44.04N   29 1.53W    short         0.07     est.
240  19/05/93   09:03     22 58.36N   28 45.93W   short         0.63     est.
241  19/05/93   11:35     23 12.60N   28 30.50W   short         0.62     est.




TABLE II: Sled tow data

Cast  Day,  Time      Position          Day,  Time      Positon
         Start     Lat        Long          End      Lat       Long
-----------------------------------------------------------------------
220   5/15, 11:13  24°15.8N   34°25.2W  5/15, 14:23  24°20.2N  34°24.6W
221   5/15, 16:33  24°20.4N   34°24.1W  5/16, 00:33  24°37.2N  34°22.9W
222   5/16, 03:08  24°53.3N   34°22.1W  5/16, 11:08  24°32.2N  34°23.8W
223   5/16, 21:30  23°36.7N   32°39.9W  5/17, 11:16  23°07.1N  32°57.5W




TABLE III: Cruise-mean CTD profile, interpolated to 10m intervals.

P (dbar)  T (°C)  S (PSU)  theta-0.3 (°C)  sigma 0.3
---------------------------------------------------------------------
10.00     22.238  37.382   22.297          27.239
20.00     22.182  37.384   22.239          27.257
30.00     22.138  37.387   22.192          27.274
40.00     22.082  37.391   22.134          27.293
50.00     22.013  37.391   22.063          27.313
60.00     21.901  37.382   21.949          27.339
70.00     21.753  37.365   21.799          27.369
80.00     21.590  37.346   21.634          27.401
90.00     21.442  37.326   21.484          27.429
100.00    21.327  37.313   21.366          27.452
110.00    21.209  37.295   21.246          27.472
120.00    21.050  37.263   21.086          27.493
130.00    20.867  37.225   20.900          27.515
140.00    20.651  37.177   20.681          27.540
150.00    20.345  37.106   20.373          27.570
160.00    19.994  37.028   20.020          27.606
170.00    19.580  36.933   19.604          27.645
180.00    19.144  36.838   19.166          27.689
190.00    18.718  36.745   18.738          27.731
200.00    18.377  36.675   18.395          27.766
210.00    18.085  36.617   18.101          27.797
220.00    17.825  36.567   17.839          27.825
230.00    17.578  36.520   17.590          27.852
240.00    17.339  36.476   17.349          27.878
250.00    17.112  36.434   17.120          27.902
260.00    16.892  36.394   16.899          27.925
270.00    16.671  36.352   16.676          27.947
280.00    16.462  36.314   16.465          27.969
290.00    16.255  36.276   16.257          27.989
300.00    16.048  36.238   16.048          28.010
310.00    15.854  36.203   15.853          28.029
320.00    15.668  36.171   15.665          28.048
330.00    15.471  36.136   15.466          28.067
340.00    15.284  36.104   15.278          28.086
350.00    15.094  36.072   15.086          28.105
360.00    14.908  36.041   14.899          28.123
370.00    14.721  36.010   14.710          28.142
380.00    14.535  35.980   14.522          28.160
390.00    14.357  35.952   14.343          28.179
400.00    14.181  35.925   14.166          28.196
410.00    14.017  35.901   14.000          28.213
420.00    13.853  35.876   13.835          28.230
430.00    13.693  35.852   13.674          28.246
440.00    13.536  35.829   13.515          28.262
450.00    13.377  35.806   13.355          28.278
460.00    13.218  35.783   13.196          28.295
470.00    13.062  35.762   13.038          28.311
480.00    12.913  35.742   12.888          28.326




TABLE IV Hydrographic properties at the target surface

Group Count P      theta   S       -dT/dp  -dS/dp  dsigma/dp  R-rho  N
            Dbar   °C      PSU      10-3    ppm/              10-3   10-3s-1
                                            dbar
                                   °C/dbar         dbar-1
----------------------------------------------------------------------------
A      7    339.3  15.592  36.151  17.1    2.88    1.79       1.81   4.15
B      18   312.6  15.624  36.161  22.0    3.96    2.10       1.69   4.49
C      15   327.1  15.594  36.151  20.5    3.64    2.00       1.72   4.39
D      17   332.3  15.657  36.170  20.4    3.56    2.04       1.75   4.43
E      8    292.5  15.676  36.176  19.5    3.49    1.90       1.71   4.27
F      9    298.5  15.724  36.191  20.4    3.67    1.97       1.70   4.35
G      6    304.4  15.665  36.173  18.7    3.21    1.92       1.78   4.30
H      11   294.2  15.761  36.202  17.6    3.12    1.75       1.73   4.10
I      18   322.2  15.662  36.172  18.9    3.29    1.91       1.76   4.28
J      15   319.4  15.657  36.170  20.0    3.50    2.00       1.74   4.38
K      9    325.6  15.607  36.155  18.4    3.17    1.87       1.77   4.24
L      8    343.7  15.589  36.150  17.6    3.00    1.84       1.80   4.20
M      19   348.6  15.632  36.163  18.2    3.12    1.88       1.79   4.25
N      7    293.6  15.631  36.163  22.7    4.05    2.18       1.70   4.58
                                           
All    166  321.2  15.640  36.165  19.4    3.40    1.93       1.74   4.31




TABLE V: Regional Groups of Stations.

Group  Casts
---------------------------
A        5 - 10
B       27 - 33, 38, 41 - 49
C       50 - 62, 65, 100
D       21 - 26, 101 - 111
E      112 - 119
F      120 - 128
G      129 - 134
H      147 - 149, 151 - 158
I       12 - 20, 159 - 167
J      168 - 182
K      183 - 191
L      191 - 198
M      199 - 217
N      224 - 230




TABLE VI: GC calibration

File     Date  Time  Std  Stds       Fit*    A          B        C     Max
                     Loop                                              Error
-----------------------------------------------------------------------------
GC A
2SA      24/4  1015  1    1.6-1.1    L/C  -0.000      0.047    340.5   111.28
24SA     27/4  0400  1    1.6-1.2    L/C   0.00004    0.011    358.7   205.29
34SA     28/4  0940  1    1.6-1.2    L/C   0.00004    0.0088   361.8   96.72
47SA     30/4  0000  1    1.6-1.2    L/C   0.00003    0.0159   361.2   406.29
57SA     1/5   0400  1    1.6-1.2    L/C   0.00003    0.0165   372.1   417.46
111SA    3/5   0100  1    1.6-1.2    L/C   0.00003    0.0104   365.34  136.2
128SA    5/5   0400  1    1.6-1.2    L/C   0.00007    0.0103   348.3   345.37
140SA    6/5   1030  1    1.6-1.2    L/C  -0.000002   0.0517   358.67  466.5
140SAS   6/5   1300  1/3  1.4-1.1    C     0.000001   0.00009  121.41  186.6
151SA    7/5   2000  1/3  1.4-1.1    L/C   0.000003  -0.0091   126.88  216.45
                                     C     0.000003  -0.0083   129.07    
157SA    9/5   0100  1    1.6-1.2    C     0.000021   0.0065   352.45  313.88
163SA    9/5   1600  1    1.6-1.1    L/C  -0.000006   0.0733   363.87  446.69
180SA    11/5  0630  1    1.6-1.1    L/C  -0.000002   0.0541   372.40  1823.3
189SA    12/5  0250  1    1.6-1.1    L/C   0.0000003  0.0382   383.5   114.13
208SA    14/5  0300  1    1.6-1.2    L/C   0.00006    0.0137   376.47  281.97
224SA    16/5  2110  1    1.6-1.2    L/C  -0.000004   0.0635   380.79  255.04
228SA    18/5  1300  1    1.6-1.2    L/C   0.000063   0.0535   368.93  291.64
GC B
3SB      24/4  1700  1    1.6-1.1    L/C  -0.0000     0.187    704.17  1337.9
19SB     26/4  1820  1    1.6-1.2    L/C   0.00018    0.0113   712.22  980.0
39SB     29/4  0200  1    1.6-1.2    L/C   0.002      0.0125   710.33  1066.4
59SB     1/5   0800  1    1.6-1.2    L/C   0.00015    0.0232   707.73  377.08
111SB    3/5   0000  1    1.6-1.2    L/C   0.00022    0.0026   695.4   1673.0
128SB    5/5   0125  1    1.6-1.2    L/C   0.00024   -0.0010   691.19  1960
140SB**  6/5   1000  1    1.4-1.1    C    -0.00003    0.1562   643.62  1717.7
140SBS   6/5   1300  1/3  1.4-1.1    C     0.000002   0.0050   222.48  176.54
150SBS   7/5   2100  1/3  1.4-1.1    C     0.000002   0.0047   234.83  244.38
163SB    9/5   1600  1    1.6-1.2    L/C   0.00181    0.093    699.95  673.62
179SB    11/5  0300  1    1.6-1.1    L/C   0.000034   0.159    703.04  742.65
199SB    13/5  0600  1    1.6-1.2    L/C  -0.000045   0.190    702.44  402.65
220SB    15/5  1255  1    1.6-1.2    L/C   0.00055    0.0089   701.11  874.16
223SB    17/5  0830  1    1.6-1.2    L/C   0.000249   0.0113   699.42  1527.56
230SB    18/5  0815  1    1.6-1.2    L/C  -0.00006    0.2403   688.63  1724.73

L/C - linear cubic
C - cubic
** Calibrated across cubic range only



APPENDIX 1: CTD CALIBRATIONS

CTD System

During the cruise 202 CTD casts were completed using an RVS Neil Brown MkIII CTD 
(s/n 01-1195) and WHOI 24 bottle rosette pylon and frame. Despite a few breakdowns 
at the start of the cruise the system worked very well and only three hours were lost 
when the CTD cable was re-terminated. Also 5 casts were completed using the sled 
and winch control system.

CTD Calibration

Temperature: The CTD temperature calibration was found to have drifted by less than 
one milli-degrees from last year's NATRE cruise and was therefore left unchanged.

Pressure: The pressure reading had increased by 4.7 decibars compared with last 
year and this was subtracted from the data.

Salinity: Salinity samples were taken from 24 casts (Table A1). An average offset of 
28ppm was found from the first 10 casts and this was added to the CTD data. The 
last 10 casts showed that the CTD remained in calibration for the rest of the cruise.

Table A1: Salinity calibrations using Autosal. Note CTD was re-calibrated after station 
53. Archived data for stations 1-53 were re-calculated using the new calibration.

Cast Number  Samples  Reading

1            23       0.0348
2            24       0.031
4            23       0.0289
10           24       0.0288
13           24       0.0277
22           24       0.0272
27           24       0.0282
31           24       0.0264
45           19       0.0262
48           23       0.0256
53           24      -0.001
60           16      -0.0011
100          22      -0.0011
115          18      -0.0005
147          24      -0.0002
151          24      -0.0013
156          24      -0.002
163          24       0.0004
176          24       0.0001
205          24      -0.0014



APPENDIX 2: CONFIGURATION AND USE OF THE ROSETTE SYSTEM

24 5-litre Niskin bottles were needed to sample vertical distribution of SF6. A 43" 
rosette frame and a 60" cage were borrowed from the WHOI CTD group. There was 
an upper section to the cage that housed a General Oceanics pylon, rosette and 
Niskin bottles.

The lower section housed a Neil Brown CTD hung vertically from an "A" bracket below 
the pylon. The vertical distance from the T and C probes to the centre of the Niskin 
bottles was 112cm. Three sets of shock cords were wrapped around the lower 
section of the CTD and to three legs of the cage 120° apart. A 31" shock cord was 
wrapped around the CTD and a 15" shock cord was wrapped around the cage leg. 
Hooks were taken out of the ends of one of the shock cords, and the hooks from the 
other were inserted into it. The cords were wrapped in vulcanising tape and a tie wrap 
was put on the end of the cords near where they went around the CTD. This turned out 
not to be a good idea. All of the stretch of the shock cord was taken in the short length 
of cord that was not taped. One of the cords gave out near the end of the cruise and 
was replaced by a new cord and not wrapped in tape. This new one showed no signs 
of strain whereas the wrapped ones showed cracking and necking down after the first 
couple of casts.

About 525lbs of weight, in the form of 28lb slugs of lead from the WHOI Stockroom, 
were added to the bottom ring and vertical pipes of the lower cage. These were held 
in place by hose clamps. Adding this weight enabled the cage to be lowered at about 
30m/min to about 50m, and then the speed slowly increased to about 60m/min while 
maintaining a tension on the CTD wire of between 500 and 1000lbs.

Considerable corrosion appeared on the rosette rings and the aluminium stanchion 
on which the rosette was mounted after the first few casts. More and larger anodes 
were added to both rosette rings and the stanchion and this seemed to alleviate the 
problem.



APPENDIX 3: CAROUSEL PUMP AND VALVE

For the fall 1992 and spring 1993 sampling cruises, OC253 and CD78, a carousel 
with more syringes was needed due to the spreading of the SF6 patch. A 50-port valve 
was built by McLane for the greater number of samples required. Along with this, new 
software was written to run this valve and pump combination.

When the valve was first tested before OC253, the valve would not mechanically return 
to the home, valve position 1, although it indicated it was home in the software. There 
are two microswitches in the valve. One counts revolutions and the other counts valve 
position. It was thought that if the microswitch that indicated valve position was wired, 
fine adjustments could be made to align the valve mechanically. This did not work. On 
OC253 in order to "fool" the software into thinking the valve was home, the pump 
would first be programmed for deployment. The valve would then have to be 
mechanically turned with a screwdriver to align it to the home position. This was 
difficult to do due to the position and stiffness of the valve.

Before CD78, two things were done to make the valve more user-friendly. Firstly, the 
microswitch to indicate revolutions was hooked back up so that when the valve was 
commanded to go home, it obeyed. Second, new software was written for the 50-port 
valve called PUMP1_47.BAS. It had menu commands to enable small adjustments to 
the valve from the keyboard to align the valve in the home position. It was found that 
due to backlash of the stepping motor, trying to move the valve one step of the motor 
wouldn't work. The software was modified to make the stepper motor go twenty steps, 
which is a small movement compared to one valve position. This worked fine. The 
software version to do this is called PUMPADJ.BAS, and is installed into the tattletale 
in place of PUMP1_47.BAS.

The pump and 50-port valve system, on the sled, was used four times on CD78, with 
the sled towed at 2 to 2.5kts. In addition to a depressor weight of 500lbs, hung below 
the sled, about 300lbs of lead weight, in the form of 28lb slugs, were added to the 
sled frame. The resulting wire angle was around 45° at 2.3kts. The direction of tow 
was constrained by the need to have the wind on the starboard side. An effective 
sampling programme with the carousel system will usually require towing from the 
stern.

With the exception of a couple of syringes which only partially filled, the pump and 
valve worked well. It was again started by a lanyard switch hooked to a General 
Oceanics pylon. When that position was tripped from the deck unit, two pins on the 
pump electronics housing were shorted to enable the pump. Mechanical alignment of 
the valve to the home position was not a problem on this cruise either. At the end of 
each cast, the valve returned almost to its proper position; when the alignment pin 
was inserted, a small amount of force on the pin was all that was needed to put the 
valve in the proper place for deployment. Therefore, though we had the capability to 
align the valve using the computer keyboard, it was not needed.


