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CRUISE REPORT: AR04EW / AR15
(Updated FEB 2009)


A.1  HIGHLIGHTS

                         CRUISE SUMMARY INFORMATION

           WOCE section designation  AR04EW / AR15
  Expedition designation (EXPOCODE)  33LKETAMBOT2_1
      Chief Scientist & affiliation  Yves Gouriou/ORSTOM*
                              Dates  1996 APR 15 - 1996 May 16
                               Ship  R/V EDWIN LINK
                      Ports of call  Leg 1: Cayenne, French Guiana to 
                                            Natal, Brazil
                                     Leg 2: Natal, Brazil to 
                                            Cayenne, French Guiana 
                 Number of stations  95
                                                08°24.03'N
              Geographic boundaries  34°54.39'W             51°33.85'W
                                                04°46.91'S

       Floats and drifters deployed  0 Floats,   0 Drifters
     Moorings deployed or recovered  0 Deployed, 0 recovered
               Contributing Authors  C. Andrié   B. Bourlès   F. Baurand   
                                     R. Chuchla  P. Fournier  Y. Gouriou  
                                     C. Oudot    J.F. Ternon


               *Yves Gouriou • Centre ORSTOM de Brest IFREMER
                      B.P. 70 Plouzane, 29280 • FRANCE 
     Tel: 33-98-22-4515 • Fax: 33-98-22-4545 • Email: gouriou@orstom.fr







A.2  CRUISE SUMMARY

CRUISE TRACK

The cruise track and station locations are shown in Figure 1.

First leg:    Cayenne (4°51’N-52°15’W) to Natal (5°48’S-35°18’W).
Second leg:   Natal (5°48’S-35°18’W) to Cayenne (4°51’N-52°15’W).

NUMBER OF STATIONS

A total of 95 CTD/rosette stations were occupied using a General Oceanics 
24 bottle rosette equipped with:

  • 24 8-liter Niskin water sample bottles .
  • a NIBS Mark IIIa CTD equipped with an oxygen sensor, and bottom 
    proximity alarm.
  • a 12 kHz MORS pinger.
  • a 150 KHz-RDI L-ADCP (Lowered Acoustic Doppler Current Profiler).

To install the L-ADCP, 2 Niskin bottles have been removed from the rosette.

SAMPLING

Double casts were performed for deep stations (bottom > 4000 m). During the 
first cast 6 water samples were taken between the surface and 500 m, and 
during the second cast 22 water samples were taken between 500 m and the 
bottom. The number of water samples per station is distributed as follows:

16 shallow stations with less than 22 water samples.
51 stations with 22 water samples.
27 stations with 28 water samples (double casts).

Salinity, dissolved oxygen, nutrients (nitrate, nitrite, silicate, 
phosphate) have been measured for every sample, at every station.

Freons (11 and 12) measurements were performed at every station. Between 
the surface and the bottom for 94 stations.

Total dissolved CO2 and pH measurements were carried out for all the closed 
bottles every other station (47 stations).

Surface sampling were carried out at each station to determine CO2 fugacity 
and Chlorophyll.

Test stations:

Station N°31: all the bottles closed at 1000 m depth.
Station N°42: all the bottles closed at 2000 m depth.
Station N°72: all the bottles closed at 2000 m depth.
Station N°87: all the bottles closed at 1000 m depth.

At every station 2 bottles were closed at the same depth.

FLOATS, DRIFTERS, AND MOORINGS

No floats, drifters, or moorings were deployed during this cruise.


A.3  LIST OF PRINCIPAL INVESTIGATORS

TABLE 1. Principal investigators

         _____________________________________________________
         
          Name                  Responsibility    Institution
          --------------------  ----------------  -----------
          Chantal Andrié        Freons            ORSTOM
          Bernard Bourlès       S-ADCP, Salinity  ORSTOM
          Yves Gouriou          CTD, L-ADCP       ORSTOM 
          Claude Oudot          Nutrients – O(2)  ORSTOM
          Jean-François Ternon  CO2 parameters    ORSTOM
         _____________________________________________________


A.4  SCIENTIFIC PROGRAM AND METHODS

The principal objectives of the cruise were:

  • To estimate the inter-hemispheric transport of heat, freshwater, 
    nutrients, CO2, and CFCs in a key region of the Atlantic ocean.
  • To estimate the seasonal variability of the deep circulation. An other 
    cruise, ETAMBOT1, has been made in an opposite season.
  • To repeat the survey of the western equatorial Atlantic ocean made 
    during the CITHER 1 cruise in January- March 1993 (Western part of the 
    A6 section).

The instruments employed in the measurement program consisted of a NBIS 
Mark IIIa CTD and General Oceanics rosette. Subsidiary instrumentation 
consisted of a 12 kHz pinger, a bottom proximity alarm, and a L-ADCP. 4 SIS 
reversing pressure meters and 4 SIS reversing thermometers were installed 
on the bottles.

After a cast the rosette was placed on the deck and secured. The rosette, 
the frame, sensors and L-ADCP were watered with fresh water. L-ADCP binary 
data were downloaded on a PC. Digital instrumentation was read and samples 
were drawn in the following order:
Freons,  oxygen, CO2 parameters, nutrients, and salinity.
The rosette was stored on deck throughout the cruise and all sampling was 
performed there.

Acoustic Doppler Current Profiler (ADCP) measurements were made 
continuously employing a hull mounting 150 kHz unit manufactured by RDI.

No continuous water depth measurements were performed along the track of 
the ship. 


A.5  MAJOR PROBLEMS ENCOUNTERED ON THE CRUISE

(1) The salinity sensor of the first CTD probe (n°2756) stopped working 
    normally at station N°9. That station has been occupied again at the 
    end of the cruise (station N°90). We replaced the probe with the spare 
    one (n°2782) at station N°10. Inspection of the first probe, during the 
    call in Natal, showed that the failure was due to the fast temperature 
    sensor of the probe.

(2) The power supply of the first Deck Unit was insufficient to correctly 
    supply the second CTD probe (n°2782). So the conductivity profiles of 
    stations N° 10 to 13 were noisy. We solved that problem at station N°14 
    by replacing the Deck Unit. The stations N°4 to N°10 and station N°13 
    have been sampled again at the end of the cruise (stations N°88 to 95).

(3) From station N°14 the oxygen sensor of the CTD probe (n°2782) did not 
    work well. Few profiles of oxygen have been made during the first part 
    of the cruise.

(4) The salinity sensor of the second CTD probe (n°2782) was deteriorated 
    at our arrival in Natal. We changed the probe after the call, replacing 
    the fast temperature sensor of the probe n°2756 by the sensor of the 
    probe n°2782. This CTD probe (n°2756) worked well during the second 
    part of the cruise (and the oxygen sensor too).

(5) The acoustic bases of the deep sounder never worked during the cruise. 
    This failure could have compromised the entire cruise, but:

    a) the track of the ETAMBOT 2 cruise was similar to the track of  the 
       ETAMBOT 1 cruise. So we knew more or less the depth at the station 
       position.
    b) we used a mechanical system that rings in the laboratory when the 
       rosette is close to the bottom, generally 15 m above,  but for this 
       cruise we stopped the rosette about 25 m above the bottom.

The vertical penetration of the S-ADCP acoustic signal was only 100 m when 
the ship was on route. This weak vertical penetration was certainly due to 
turbulence close to the well where the ADCP was placed in. During the 
stations, when the ship stopped, the vertical penetration of the 
measurements was about 300 m. 


A.6  LIST OF CRUISE PARTICIPANTS

TABLE 2. Cruise participant
    ____________________________________________________________________
    
     Name                  Responsibilities            Affiliation  Leg
     --------------------  --------------------------  -----------  ---
     Chantal Andrié        CFCs                        ORSTOM       1-2
     François Baurand      Nutrients                   ORSTOM       1-2
     Jean-Michel Bore      Elec. Engineer/CTD/L-ADCP   ORSTOM       1-2
     Bernard Bourlès       CTD/S-ADCP/Salinity         ORSTOM       1-2
     William Biegun        CFCs                        ORSTOM       1-2
     Rémy Chuchla          CTD/Salinity                ORSTOM       1-2
     Denis Diverres        CO2                         ORSTOM       1-2
     Philippe Fournier     Oxygen                      ORSTOM       1-2
     Yves Gouriou          Chief Scientist/CTD/L-ADCP  ORSTOM       1-2
     Christophe Le Doare   CTD/L-ADCP                  ORSTOM       1-2
     Frédéric Marin        CTD/salinity                ORSTOM       1-2
     Yves Montel           Nutrients                   ORSTOM       1-2
     Claude Oudot          CO2                         ORSTOM       1-2
     Jean-François Ternon  CFCs                        ORSTOM       1-2
    ____________________________________________________________________
        ORSTOM: Institut Français de Recherche Scientifique pour le 
                      Développement en Coopération



B.  UNDERWAY MEASUREMENTS

B.1  NAVIGATION
     (B. Bourlès)

Navigation data (time, position, course and speed over ground, and fix 
quality information) were acquired every 15 seconds throughout the ETAMBOT-
2 cruise, from the 04/15/1996 at 18h50 TU to the 05/16/1996 at 10h55 TU, 
with the vessel Magnavox MX200 Global Positioning System (GPS). The GPS was 
located in the bridge, and navigation information were transmitted to a 
Personal Computer dedicated to navigation and thermosalinograph measurement 
acquisition, located in the main laboratory. 

Due to a not clarified network problem between the bridge and the 
laboratory, the registered time was erroneous, yet the position (latitude 
and longitude) was correct. As the internal acquisition PC clock, and the 
internal L-ADCP clock, were perfectly synchronized, we used the 
acquisition-PC clock for time reference. Thus, we registered this PC time 
at the beginning and at the end of every CTD-O2 station during the cruise, 
and used these time reference values to correct the GPS time information, 
hence the navigation. We first linearly constructed a time reference data 
base, and then attributed the ‘true’ position to the correct time, using a 
2 minutes time filter. Navigation measurements were also acquired by the S-
ADCP acquisition system (see chapter B3), using the RDI ‘GPRMC’ software. 
This software calculates the average of GPS successive information around 
the velocity acquisition times, and registers ‘mean’ navigation every 
5 minutes. The re-calculated navigation data are in very good agreement 
with this navigation data base (differences are of the order of 1/100 
minute), and has been used with confidence for L-ADCP data treatment (see 
chapter B4). 



B.2  ECHOSOUNDING

None.



B.3  ACOUSTIC DOPPLER CURRENT PROFILER (ADCP)
    ( B. Bourlès)

The S-ADCP system on board the R/V EDWIN LINK is a 153 kHz RD-VM150 
Instruments unit with a hull mounted transducer. The four-beam transducer 
is mounted in a open sea well, and located to port side around the vessel 
centerline at about 3 meters depth. It is connected by cable to a deck box, 
containing the processing equipment, and connected to a Personal Computer 
(AT-286) dedicated to measurement acquisition. Ship’s gyrocompass 
information are collected by the deck box through a synchro to digital 
interface. Data were collected using the RDI Data Acquisition Software 
(version 2.48). Information exchanges between the S-ADCP and the 
acquisition PC were managed by the ‘ENSOUT’ RDI software. Navigation data 
(time, position, course and speed over ground, and fix quality information) 
were acquired with a Magnavox MX4200 Global Positioning System (GPS). 
Standard setup parameters used were: 8 meter bin and pulse lengths, 4 meter 
blanking, and 5 minutes ensemble averaging. A reference layer was defined 
between bins 5 to 15. The first bin was centered at 16 meter depth. Sea 
salinity value, necessary to calculate the sound velocity during data 
acquisition, was fixed to 25 off French Guiana because of the influence of 
fresh Amazon water, and to 35 or 36 (considering the thermosalinograph 
measurements) in the open sea. The S-ADCP data processing has been made 
using the Common Oceanographic Data Access System (CODAS-3, version 3) of 
the Hawaii University (Bahr et al., 1990). The PC clock drift is first 
determined by comparing PC time with GPS time. The corrected time is then 
included in the data base. Navigation and transducer temperature are first 
checked. ‘Noisy’ bins or profiles are suppressed. Due to the location of 
the transducer, and to the presence of turbulence along the hull during the 
vessel course, current velocity profiles were only available during CTD 
stations, when vessel was stopped. Navigation and S-ADCP measurements are 
combined in order to obtain absolute current values. The current velocity 
is calibrated using the Pollard and Read (1989) standard procedure. 

Absolute velocity profiles were obtained down to about 350 m depth. The 
original 5 minutes profiles have been averaged into ‘in stations’ profiles; 
96 mean velocity profiles are thus available. Standard deviation of 
velocity mean profiles is of the order of 3 cm s^-1.


REFERENCES

Bahr, F., E. Firing and S. Jiang, Acoustic Doppler current profiling in the 
    western Pacific during the US-PRC TOGA Cruises 5 and 6, JIMAR Contr. 
    90-0228, U. of Hawaii, 162 pp., 1990.
Pollard, R. and J. Read, A method for calibrating shipmounted acoustic 
    Doppler profilers, and the limitations of gyro compasses, J. Atmos. 
    Oceanic Technol., 6, 859-865, 1989.



B.4  L-ADCP MEASUREMENTS
     (B. Bourlès, Y. Gouriou, R. Chuchla)

The Lowered Acoustic Doppler Current Profiler (L-ADCP) allows to provide 
absolute currents over the whole water column. The L-ADCP is a BroadBand 
150 kHz RD Instruments unit. It was attached to the ‘rosette’, and two 
water bottles had to be removed from the ‘rosette’ frame for L-ADCP 
installation. The L-ADCP acquires velocity profiles during the down and up 
casts, simultaneously to the CTD-O2 system. The CTD-O2/L-ADCP package was 
lowered and raised at about 1 m s^-1, except during the up-cast when the 
package was stopped to fire the bottles. Standard setup parameters used 
were: one second sampling rate, one ping per ensemble, 19 bins per 
ensemble, 16 meter bins width, sea water salinity of 35 and sound velocity 
of 1500 m s^-1. Thus, a velocity profile of about 300 m vertical extent is 
acquired every second. Each ensemble contains the precise time, internal 
sensor temperature, heading, pitch and roll angles, and vertical velocity 
of the rosette. Data of each bin contain the three velocity components in 
earth coordinates, velocity error estimate, backscattered energy and 
quality parameters (e.g., ‘percent good’). Data have been processed 
following the method described by Fischer and Visbeck (1993), and adapted 
by Gouriou and Hémon (1997). As the L-ADCP did not have pressure sensor, 
the depth of each cell was computed using the vertical velocity 
measurements. Then, all the individual profiles were combined in a unique 
velocity profile over the whole water. At depth, data of the bins perturbed 
by the bottom reflections were suppressed. The reference velocity was 
determined using the precise time and position at the beginning and at the 
end of the profile, generally known thanks to a Global Positioning System 
(GPS). Error due to this reference velocity determination is estimated to 
1 cm s^-1 (Fischer and Visbeck, 1993). Here, due to GPS time transmission 
problems (see navigation chapter), we used the time of position 
recalculated from ‘true’ navigation information. However, the precision of 
the L-ADCP measurements is difficult to evaluate at this stage, except in 
the surface layers by comparison with Ship mounted Acoustic Doppler Current 
Profiler measurements, where maximum mean differences reach 5 cm s^-1. 

The L-ADCP perfectly worked during all the CTD-O2 casts; hence, ninety-nine 
absolute velocity profiles were acquired during the Etambot-2 cruise.


REFERENCES

Fischer, J., and M. Visbeck: Deep velocity profiling with self_contained 
    ADCPs, J. Atmos. Oceanic Technol, 10(5), 764-773, 1993.
Gouriou, Y., and C. Hémon: Traitement des données L-ADCP, Centre ORSTOM de 
    Cayenne, documents scientifiques n° O.P. 21, 56pp, 1997.



B.5  THERMOSALINOGRAPH MEASUREMENTS
     (B. Bourles)

Continuous underway measurements of surface salinity and temperature were 
made with a Seabird SBE-21 shipboard mounted thermosalinograhp (TSG), 
calibrated one month before the cruise. Waters amples were taken below the 
sea surface at the forward side of the vesssel, and forwarded thanks to a 
pump to the thermosalinograph, located in the main acquisition laboratory. 
TSG measurements were acquired every 15 seconds. As the sampling hole was 
certainly too close to the surface, air bubbles contamined waters amples 
during vessel course, due to pitch and roll, when rough sea conditions 
occurred (mainly at the beginning of the cruise and off the Amazon mouth). 
There, raw measurements were noisy and exhibited numerous picks or 
erroneous values. In the same way, due to unpowerfull pumping, salinity 
linearly decreased on station, when vessel is stopped. Thus, a first 
visualization allowed to eliminate every erroneous or doubtful TSG 
measurement. A second step consisted to filter the measurements 
(temperature and salinity in a same processing), by using a median filter 
(Henin and Grelet, 1996). We kept the median T/S values over a 15-minute 
time window, after discarding T/S values more than five standard deviations 
from the mean calculated over the window. Thus, TSG measurements have been 
filtered and averaged over 15 mn time intervals. However, a comparison with 
sample salinity measurements and CTD-O2 temperature measurements is 
necessary before every quantitative use of the TSG data.


REFERENCE

Henin, C., and J. Grelet: A merchant ship thermo-salinograph network in the 
    Pacific ocean, Deep-Sea Res., 43, 11-12, 1833-1855, 1996.



B.6  XBTs



B.7  METEOROLOGICAL MEASUREMENTS
     (B. Bourlès)

Meteorological measurements were recorded at the beginning of every CTD-O2 
station. These measurements are the following: date, time, position, wind 
speed (m s^-1), wind direction (degrees from geographical north), sea level 
pressure (mbar), sea level temperature (°C), and relative humidity (%). 
Weather, clouds and sea level conditions have not been recorded. 



C.  HYDROGRAPHIC MEASUREMENTS TECHNIQUES AND CALIBRATIONS

C.1  SAMPLE SALINITY MEASUREMENTS
     (P. Fournier and C. Oudot)

Salinity analysis of samples collected during ETAMBOT 2 were carried out 
onboard with a Guildline(TM) Portasal(TM) salinometer model 8410, 
equipped with an OSI (Ocean Scientific International) peristaltic-type 
sample intake pump. The instrument was operated in the container-laboratory 
kept at a constant temperature of 23°C. The bath temperature of the 
salinometer was adjusted to 24°C. Standardization was effected by use of 
IAPSO Standard Seawater batch P123 (K(15) = 0.99994). 

Every day, the standardization was adjusted before one run of analysis and 
the standardization drift was checked every two stations (44 samples). The 
drift was very low: on the average it was – 0.00002 ± .00045 psu.

Quality control of the salinity data were performed using repeated 
measurements from replicate samples (all bottles fired at the same depth, 
twice) and duplicate samples (two different bottles fired at the same 
depth, seventy-four times). The standard deviations of the two groups of 
replicate samples are given in the Table 3 below.


TABLE 3. Salinity replicate statistics

            ________________________________________________
            
             Station number              42         72
             -----------------------  ---------  ---------
             Pressure (dbar)          2020       2500
             Number of bottles          22         22
             Mean salinity (psu)        34.9772    34.9504
             Maximum deviation (psu)     0.0013     0.0012
             Standard deviation          0.0005     0.0005
            _______________________________________________


The standard deviation of the seventy-four sample pairs (duplicate), taken 
at different depths, is 0.0010 psu.



C.2  SAMPLE OXYGEN MEASUREMENTS
     (P. Fournier and C. Oudot)

SAMPLING AND TECHNIQUES 

Oxygen samples were taken in calibrated clear glass bottles (capacity = 120 
cm^3) immediately after the drawing of samples for CFCs. The temperature of 
the water at the time of sampling was measured to allow the conversion of 
the concentration unit per volume into per mass. The fixing of the 
dissolved oxygen is immediately performed with reagents before the closure 
of the glass bottle, according to the method recommended in the WOCE 
Operations Manual (Culberson, 1991). The samples were stored in the 
container-laboratory (controlled temperature of 22 ± 1°C) where analyses 
were carried out, according to the Winkler whole bottle method.

All volumes of glassware to collect samples and to dispense solutions were 
calibrated by weight and corrections were made for changes in volume with 
temperature.

The end-point was determined by automatic potentiometric method with a 
Metrohm(TM) Titrator(TM) model 682 and a Dosimat(TM) 665 burette (10 
cm^3).

The concentration of oxygen dissolved in seawater was converted to mass 
fraction by use of the following relationship:

          O2 [µmol kg^-1] = (44.660 / ρ(sw)) * O2 [cm^3 dm^-3]

where r(sw) is the density of the seawater corresponding to the temperature 
at the sampling time (Millero and Poisson, 1981).

REPRODUCIBILITY OF MEASUREMENTS

The precision of measurements was estimated from analysis of four groups of 
replicate (taken from different bottles fired at the same depth) samples 
and a large number (seventy-nine) of duplicate (two bottles fired at the 
same depth, changing from one station to the other) samples during 
successive stations. Table 4 gives the statistics of replicates.


TABLE 4. Oxygen replicate statistics

   ____________________________________________________________________
   
    Station number                        32      42      72      87
    ----------------------------------  ------  ------  ------  ------
    Pressure (dbar)                     1030    2020    2500    1000
    Number of bottles                     22      22      22      22
    Mean O2 concentration (µmol kg^-1)   152.0   255.1   259.0   153.1
    Maximum deviation (µmol kg^-1)         0.7     0.6     0.3     1.7
    Standard deviation (µmol kg^-1)        0.7     0.2     0.4     0.6
   ____________________________________________________________________


The standard deviation of the seventy-nine sample pairs (duplicate) is 0.5 
µmol kg^-1, i.e a value not significantly different from reproducibility of 
replicates.

COMPARISONS WITH HISTORICAL DATA

Comparisons of ETAMBOT 1 data with historical data (SAVE Leg 6, 1989 and 
TTO-TAS, 1983) are shown in Figure 2. The right insets exhibit the deepest 
levels. Excepted differences in the upper layers resulting from changes in 
water masses in the region, principally in bottom panel (TTO-TAS) where the 
latitude range is wider, the agreement is satisfactory.


REFERENCES

Culberson C.H., 1991. Dissolved oxygen in the WOCE Operations Manual. Vol. 
    3, Part 3.1.3: WHP Operations and Methods. WHP Office Report WHPO 91-1, 
    WOCE Report N° 68/91.
Millero F.J. and  A. Poisson, 1981. International one-atmosphere equation 
    of state of Sea Water. Deep Sea Res., 28, 625-629.



C.3  NUTRIENTS 
     (F. Baurand and C. Oudot)

EQUIPMENT AND TECHNIQUES

Nutrient analyses were performed on a Braun & Luebbe(TM) AutoAnalyzer(TM)II 
type Technicon (continuous flow analyzer), according to classical methods  
(Murphy and Riley, 1955 for silicate – Murphy and Riley, 1962 for phosphate 
– Wood et al., 1967 for nitrate and nitrite) as described in the Manual of 
Treguer and Le Corre (1975). Colorimeter signals were processed with an IBM 
computer using a home-made software (Lechauve et al., 1992).

Sampling for nutrient analysis followed those for gases (freons, oxygen, 
CO2 fugacity, total CO2 and pH) and were carried out in Nalgene bottle (125 
Cm^). Samples were stored until analysis (the maximum delay is six hours) 
in the container-laboratory controlled in temperature (22°C). The Nalgene 
bottles were put on the special sample tray of the AutoAnalyzer in such a 
way as the samples were directly taken from the sampling bottles without 
transfer via traditional polystyrene cups.

CALIBRATION AND STANDARDS

Volumes of glassware (volumetric flasks and Metrohm(TM) automatic burette 
model Dosimate(TM) 665) to prepare standards were checked by weight in the 
shore-laboratory, at a temperature near that in the container-laboratory 
(22°C). 

Nutrient primary standards were prepared from salts (Baker(TM), anal. 
grade., certified 99.99%, for phosphate, nitrate and nitrite; Carlo 
Erba(TM), high purity for silicate) dried at 105°C for two hours. Four 
primary standards were prepared ashore prior the cruise by dissolving:

  • 0.85056 g of potassium dihydrogenophosphate in 1 liter of ultrapure 
    water
  • 12.63875 g of potassium nitrate in 1 liter of ultrapure water
  • 8.62500 g of sodium nitrite in 1 liter of ultrapure water
  • 2.35075 g sodium silica fluoride in 5 liters of ultrapure water

No buoyancy correction were applied to the nominal weights. The ultrapure 
water was deionized water with a resistivity of 18 M Ω. The primary 
standard solutions were preserved with chloroform (2 ml per liter).

A mixed secondary standard for phosphate + nitrate and a single secondary 
standard for nitrite were prepared weekly by dilution with deionized water. 
Seven working standards were prepared every day in artificial water. 
Concentrations (µmol l^-1) were: 0, 10, 20, 40, 60, 90, 120 for silicate; 
0, 0.25, 0.50, 1.00, 1.50, 2.50, 3.00 for phosphate; 0, 5, 10, 20, 30, 40 
for nitrate; 0, 0.50, 1.00, 1.50, 2.00 for nitrite. The artificial seawater 
was a 40 ‰ solution of analytical grade sodium chloride.

The linearity of the calibration curve (Beer’s Law) was not valid beyond 20 
µmol l^-1 for silicate and nitrate. So, a polynomial (cubic) relationship 
was chosen for those nutrients.

QUALITY CONTROL

The precision of measurements was estimated from analysis of four groups of 
replicate (taken from different bottles fired at the same depth, during 
four test stations) samples and a large number (seventy-four) of duplicate 
(two bottles fired at the same depth, changing from one station to the 
other) samples during successive stations. Table 5 gives the statistics of 
replicates. The percent standard deviations (vs. full range) are 0.3% for 
silicate, 0.4% for phosphate and 0.2% for nitrate, in agreement with WHP 
recommendations (WOCE, 1994). 


TABLE 5. Nutrient replicate statistics

SILICATE
______________________________________________________________________________
 
 Station number                              32       42       72       87
 ----------------------------------------  -------  -------  -------  -------
 Pressure (dbar)                           1000     2000     2500     1000
 Number of bottles                           22       22       22       22
 Mean silicate concentration (µmol kg^-1)    27.32    18.85    23.28    27.19
 Standard deviation (µmol kg^-1)              0.13     0.07     0.08     0.35
 Percent standard deviation                   0.48     0.39     0.35     1.27
 Percent standard deviation                   0.11     0.06     0.07     0.29
 (vs full range, 120 μmol kg^-1)
______________________________________________________________________________


PHOSPHATE
_______________________________________________________________________________

 Station number                                32       42       72       87
 ------------------------------------------  -------  -------  -------  ------
 Pressure (dbar)                            1000     2000     2500     1000
 Number of bottles                            22       22       22       22
 Mean phosphate concentration (µmol kg^-1)     2.09     1.22     1.23     2.08
 Standard deviation (µmol kg^-1)               0.01     0.01     0.02     0.01
 Percent standard deviation                    0.60     0.83     0.38     0.47
 Percent standard deviation                    0.42     0.33     0.15     0.33
 (vs full range, 3 µmol kg^-1) 
_______________________________________________________________________________


NITRATE

    ___________________________________________________________________
     
     Station number                             32       72       87
     ---------------------------------------  -------  -------  ------
     Pressure (dbar)                          1000     2500     997
     Number of bottles                          22       22      22
     Mean nitrate concentration (µmol kg^-1)    31.10    19.00   31.45
     Standard deviation (µmol kg^-1)             0.08     0.03    0.05
     Percent standard deviation                  0.27     0.17    0.15
     Percent standard deviation                  0.21     0.08    0.12
     (vs full range, 40 µmol kg^-1) 
    ___________________________________________________________________


The standard deviation of the seventy-four sample pairs (duplicate) is 0.4 
μmol kg^-1 for silicate, 0.02 μmol kg^-1 for phosphate and 0.1 μmol kg^-1 
for nitrate.

The consistency of phosphate and nitrate data is shown in Figure 3 by the 
strong correlation between these two nutrients (R^2 = 0.9935). The slope of 
the regression line (15.092) is in good agreement with the Redfield ratio.

COMPARISONS WITH HISTORICAL DATA

Comparisons of ETAMBOT 1 data with historical data (SAVE Leg 6, 1989 and 
TTO-TAS, 1983) are shown in Figure 4. The right insets exhibit the deepest 
levels. Excepted differences in the upper layers resulting from changes in 
water masses in the region, principally in bottom panel (TTO-TAS) where the 
latitude range is wider, the agreement is satisfactory.


REFERENCES

Lechauve J.J., Baurand F. and C. Oudot, 1992. Manuel d’utilisation ASTECH 
    (Analyse du Signal TECHnicon). Doc. Techn. Centre ORSTOM de Brest, n° 
    67, 35 p.
Mullin J.B. and J.P. Riley, 1955. The spectrophotometric determination of 
    silicate-silicon in natural waters with special reference to sea water. 
    Anal. Chim. Acta, 12 : 162-170. 
Murphy J. and J.P. Riley, 1962. A modified simple solution method for the 
    determination of phosphate in natural waters. Anal. Chim. Acta, 27: 
    31-36.
Tréguer P. and P. Le Corre, 1975. Manuel d’analyse des sels nutritifs dans 
    l’eau de mer (utilisation de l’AutoAnalyzer II Technicon). Université 
    de Bretagne Occidentale, Brest, 2^(eme) édition., 110 p.
WOCE , 1994. WOCE Operations Manual. Vol. 3, Part 3.1.3 : WHP Operations 
    and Methods. WHP Office Report WHPO 91-1, WOCE Report N° 68/91, 
    Revision 1, November 1994.
Wood E.D., Armstrong F.A.J. and F.A. Richards, 1967. Determination of 
    nitrate in sea-water by cadmium-copper reduction to nitrite. J. Mar. 
    Biol. Ass. U.K., 47 : 23-31.



C.4  CFC-11, CFC-12
     (C. Andrié)

WORK ON BOARD 

During the cruise, three people had in charge sampling and analysis of 
water samples for CFC measurements.

Sea water samples were directly  taken from Niskin bottles  using syringes 
with metallic stopcocks. Samples from the whole water column have been 
taken. This corresponds to at least 22 samples per profile. 28 samples have 
been taken for stations with double casts with bottom depth greater than 
4500 m (stations 22 to 26, 28 to 35, 51 to 57 and 79 to 85).

Atmospheric measurements have been realized every two days, from syringe 
samples. Globally, 3725 analyses have been realized, including standards 
and atmospheric analyses.

The usual precautions have been taken before and during the boarding: 
Niskin bottles cleaned and stored in a ventilated area in Cayenne before 
the cruise and then Decon washed on board, bottles rings heated (60°C) and 
degased in an oven just before the first station.

Important CFC links have perturbed the first analyses on board. The 
analytical system has been moved in another laboratory, without air 
conditioning. Finally, measurements were satisfactory, excepted during 
station 32 where a high F-12 blank made impossible good measurements.

ANALYSES AND DATA VALIDATION

The gas chromatographic method with electron capture detection is described 
in Bullister and Weiss (1988), with some minor modifications. The gas 
vector is ultrapure nitrogen. Validation has been done, for each station, 
from vertical F11 and F12 profiles and F11/F12 diagrams. Seven F12 data 
have been rejected (all F11 data have been kept).

The atmospheric secondary standard has been calibrated against a SIO 
primary standard during four times during the cruise. CFC concentrations 
are reported in the SIO 1986 scale. For the whole cruise, the 
reproducibility for the standard content was  ±0.4% for F12 and ±0.4% for 
F11, so better than for ETAMBOT1.

The atmospheric mixing ratios were 524.5 ppt (±1.1%) for F12 and 267.1 ppt 
(±1.2%) for F11 so in the same order of magnitude than during ETAMBOT1.
Calibration has been done using a 6 levels x^2 curve.

ANALYTICAL PERFORMANCES 

The detection limit of the method is obtained during test-stations where 
all the bottles have been closed at the same level, corresponding to a 
near-zero CFC content. Differently from CITHER 1, there is not true CFC-
free waters in the ETAMBOT area. Our mean contamination level has been 
determined through a statistical method of the test-stations, the CFC 
content evolution at 1000 m depth (low-CFC Upper Circumpolar Water) and a 
comparison with CITHER1 results.

The detection limit determined through the standard deviation over the 
test-stations at 1000 m (stations 32 and  87) is around 0.005 pmol.kg^-1 
for F12 and 0.008 pmol.kg^-1 for F11.

We have examined the evolution of the F11/F12 ratio at the 1000m level in 
order to separate the part of bottles contamination to the part of the 
sampled water. Two groups of stations are identified: the mean 
contamination levels are 0.003 pmol.kg^-1 for F12 and 0.025 pmol.kg^-1 for 
F11. These contamination levels have been systematically removed from the 
CFC values.


REFERENCES 

Bullister, J.L., and R.F. Weiss, Determination of CCl(3)F and CCl(2)F(2) in 
    seawater and air, Deep-Sea Res., 35, 839-853, 1988.



C.5  SAMPLES TAKEN FOR OTHER CHEMICAL MEASUREMENTS

CO2 SYSTEM PARAMETERS
(J.F. Ternon and C. Oudot)

TOTAL INORGANIC CARBON (TCO2)

Measurements of TCO2 were made by gas chromatography, according to the 
method described by Oudot and Wauthy (1978). The method basically consists 
of gas stripping of the seawater sample (1 cm^3) after acidification, and 
of the gas chromatographic analysis of the gas mixture allowing the TCO(2) 
separation and quantification. Routine calibration of the measurements was 
performed using liquid standard solutions prepared at the laboratory prior 
the cruise, according to a procedure adapted from the Goyet and Hacker 
(1992) technique. Primary calibration is done by using the Certified 
Reference Material delivered by A.G. Dickson (Scripps Institution of 
Oceanography).

Samples were taken from the surface to bottom, every two stations.

Quality control of TCO2 data has been performed using repeated measurements 
(duplicate) at each station (two bottles fired at the same depth; different 
depth at each station), and "test" stations (all of the bottles closed at 
the same depth). Results for test stations are shown in Table 6.


TABLE 6. TCO2 replicate statistics

      _________________________________________________________________
       
       Station number                     32      42      72      87
       -------------------------------  ------  ------  ------  ------
       Depth (dbar)                     1000    2000    2500    1000
       Number of bottles                  21      22      17      22
       TCO2 (µmol kg^-1)                2202.3  2215.9  2225.4  2201.6
       Standard deviation (μmol kg^-1)     9.1    14.2     7.7     6.1
      _________________________________________________________________


Repeatability of TCO2 measurements was determined from statistical analysis 
of duplicate results, according to the relationship (Dickson and Goyet, 
1994):
                        S = (Σd(i)^2/2n)^(1/2)

where d(i) = difference for pair i and n = number of pairs (76). For 
Etambot2 cruise S = 9.7 μmol kg^-1.

pH

The pH measurements were performed according to the potentiometric method 
on the total hydrogen ion concentration pH scale (Dickson (1993). The total 
hydrogen ion concentration, [H^+], is expressed as moles per kilogram of 
sea water.

Measurements were made using a combination glass/reference electrode 
ORION(TM) type ROSS™ and a pHmeter ORION(TM) model 720A (resolution = 0.1 
mv, i.e. 0.0017 pH units). The Nernst response of the electrode was checked 
in the shore-based laboratory before and after the cruise with two 
buffers: ‘Tris’ and ‘2-aminopyridine’. The pH electrode was calibrated 
against the ‘Tris’ buffer before every serial of measurements (every 
station), and the drift was estimated during each station (22 samples) for 
correction. The mean drift during a station, throughout the cruise, was 
0.1-0.2 mV, i.e. 0.002-0.003 pH units. Seawater samples and buffers were 
thermostated at 25°C and the temperature was measured with a platine probe 
(± 0.01°C).

Then, pH data were corrected to in situ conditions (temperature and 
pressure) according to the relationships of Millero (1995) for temperature 
and Millero (1979) for pressure.

Samples were taken from the surface to bottom, every two stations.

Quality control of pH data has been performed using repeated measurements 
(duplicate) at each station (two bottles fired at the same depth; different 
depth at each station), and "test" stations (all of the bottles closed at 
the same depth). Results for test stations are shown in Table 7.

TABLE 7. pH replicate statistics

       ____________________________________________________________
        
        Station number         32         42       72        87
        ------------------  --------  --------  --------  --------
        Depth (dbar)        1000      2000      2500      1000
        Number of bottles     21        21        22        21
        pH                     7.880     8.014     8.008     7.881
        Standard deviation     0.003     0.003     0.002     0.005
       ____________________________________________________________


Repeatability of pH measurements was determined from statistical analysis 
of duplicate results, according to the relationship (Dickson and Goyet, 
1994):
                           S = (∑d(i)^2/2n)^(1/2)

with d(i) = difference for pair i and n = number of pairs (76). For Etambot 
2 cruise S = 0.003 pH units.

TOTAL ALKALINITY

Total alkalinity, A(T), is defined as the number of moles of hydrogen ion 
equivalent to the excess of following bases formed from weak acids in one 
kilogram of sample:

     A(T) = [HCO(3)^-] + 2 [CO3^(2-)] + [B(OH)(4)^-] + [OH^-] - [H^+]

A(T), expressed in μeq kg^-1, was estimated as the sum of the components 
of the right member of the previous relationship, calculated from TCO2 and 
pH measurements. The used equilibrium equations and thermodynamic data for 
carbonic acid, boric acid and water are identical to those reported in 
Dikson and Goyet (1994).
Samples were taken from the surface to bottom, every two stations.

Quality control of A(T) data has been performed using repeated measurements 
(duplicate) at each station (two bottles fired at the same depth; different 
depth at each station), and "test" stations (all of the bottles closed at 
the same depth). Results for test stations are shown in Table 8.

TABLE 8. A(T) replicate statistics

     ________________________________________________________________
      
      Station number                    32      42      72      87
      ------------------------------  ------  ------  ------  ------
      Depth (dbar)                    1000    2000     2500   1000
      Number of bottles                 21      21      17      21
      A(T) (µeql kg^-1)               2308.7  2280.4  2397.2  2309.9
      Standard deviation (µeq kg^-1)     9.4    15.0     8.3     6.8
     ________________________________________________________________


Repeatability of A(T) measurements was determined from statistical analysis 
of duplicate results, according to the relationship (Dickson and Goyet, 
1994):
                          S = (∑d(i)^2/2n)^(1/2)

with d(i) = difference for pair i and n = number of pairs (76). For Etambot 
2 cruise S = 10.8 µeq kg^-1.

CO2 FUGACITY

The fugacity of CO2 in seawater was determined in air that was in 
equilibrium with a discrete sample of seawater. The fugacity, ƒCO2, is 
related to the partial pressure, ρCO2 , by the relation (Weiss, 1974) to 
take into account the non-ideality of CO2:

                    ƒCO2 = ρCO3 exp{(B + 2δ) ρ(atm)/RT}

The partial pressure of CO2 in wet air is calculated from the molar 
fraction of CO2 in dry air, xCO2, the atmospheric pressure, P , and the H2O 
vapor pressure, ρ(H2O)  (Weiss and Price, 1980) :

                     ρCO2 = xCO2ρ = xCO2 (P – ρ(H2O))

The molar fraction of CO2 in equilibrated air was measured with an IR 
analyzer LI-COR(TM) model LI6262 . The analyzer was calibrated with three 
standard gases (329.0 – 360.5 – 407.7 ppm), produced by a French 
manufacturer, Air Liquide, in agreement with the scale of the Scripps 
standards.  During the cruise, duplicate seawater samples were taken from 
only the surface bottle of the General Oceanics rosette and analyzed as 
described in Oudot et al. (1995). Besides, the measurement of atmospheric CO2 
concentration was made twice a day by pumping an air stream taken at a mast 
at the bow of the vessel.

Then, the CO2 fugacity measured at 28°C was corrected for in situ 
temperature according to the temperature dependence equation of Copin-
Montegut (1989).

The reproducibility of ƒCO2 measurements was determined from statistical 
analysis of 86 pairs of duplicate results, according to the relationship 
(Dickson and Goyet, 1994):

                          S = (∑d(i)^2/2n)^(1/2)

where d(i) = difference for pair i and n = number of pairs (86). For 
Etambot 2 cruise S = 2.2 µatm.


REFERENCES

Copin-Montégut C., 1989. A new formula for the effect of temperature on the 
    partial pressure of CO2 in seawater. Mar. Chem., 27, 143-144
Dickson A.G., 1993. pH buffers for seawater media based on the total 
    hydrogen ion concentration scale. Deep Sea Res., 40, 107-118.
Dickson A.G. and C. Goyet, 1994. Handbook of Methods for the Analysis of 
    the various Parameters of the Carbon Dioxide System in Sea Water. 
    Version 2, US. DOE, SGRP-89-7A.
Goyet C. and S.D. Hacker, 1992. Procedure for the calibration of a 
    coulometric system used for total inorganic carbon measurements in 
    seawater. Mar. Chem., 38, 37-51.
Millero F.J., 1979. The thermodynamic of the carbonate system in seawater. 
    Geochimica et Cosmochimica Acta, 43,1651-1661.
Millero F.J., 1995. Thermodynamics of the carbon dioxide system in the 
    oceans. Geochimica et Cosmochimica Acta, 59, 661-677.
Oudot C. and B. Wauthy, 1978. Adaptation of a gas chromatograph for 
    shipboard measurement of dissolved gases : nitrogen, oxygen and carbon 
    dioxide (in French). Cah. ORSTOM, sér. Océanogr., 16, 89-102.
Oudot C., J.F. Ternon and J. Lecomte, 1995. Measurements of atmospheric and 
    oceanic CO2 in the tropical Atlantic: 10 years after the 1982-1984 
    FOCAL cruises.
Weiss R.F., 1974. Carbon dioxide in water and seawater : the solubility of 
    a non-ideal gas. Mar. Chem., 2, 203-215.
Weiss R.F. and B.A. Price, 1980. Nitrous oxide solubility in water and 
    seawater. Mar. Chem., 8, 347-359.



C.6 CTD MEASUREMENTS

The following equipment was deployed on the CTD/multisampler underwater 
frame:

(1) Neil Brown Mark IIIa with a polarographic Beckman sensor
(2) General Oceanics 8-liter 24 bottle rosette.
(3) 6 SIS digital reversing thermometers and 6 SIS digital reversing 
    pressure meters.
(4) MORS 12 kHz pinger
(5) A bottom proximity alarm
(6) L-ADCP 150kHz RDI. 2 bottles have been removed.

CTD data were acquired through an EG&G demodulator, with the OCEANSOFT 1 
software. Data were stored on a PC. Raw analogic data were stored on DAT 
system.

The rosette was not equipped with the non data interrupt rosette firing 
module.

We had no problems with the rosette and the bottles were fired at the 
desired depths.



C.7  CTD DATA COLLECTION AND PROCESSING

Two CTD-O2 Neil Brown Mark IIIa probes have been used during the cruise.

The N°2756 probe has been used for stations N°1 to N°9. Due to a failure of 
the fast temperature sensor at station N°9, the N°2782 probe has been used 
from station N°10 to station N°64. For these stations, the oxygen sensor 
worked only for a few stations. The N°2756 probe has been repaired at the 
Natal (Brazil) port of call and used for stations N°65 to N°95. Due to a 
too weak power supply, conductivity and oxygen profiles of stations N°10 to 
N°13 are noisy. The problem was solved at station N°14.  

TEMPERATURE CALIBRATION

The temperature sensors of the two CTD probes were calibrated before and 
after the cruise.
The N°2756 probe has been calibrated on December 15, 1995, and on October 
30, 1996.
The N°2782 probe has been calibrated on December 6, 1995, and on October 1, 
1996.

The temperature sensors have been controlled for the following temperature: 
0°C, 5°C, 10°C, 15°C, 20°C, 25°C, 30°C.

PROBE N°2756

The calibration results for the N°2756 are presented on figure 5a. Between 
the pre- and post-calibration the temperature sensor presents a drift of:

  • 0.006°C in average
  • 0.008°C at a temperature of 0°C (maximum)
  • 0.000°C at a temperature of 10°C (minimum).

We considered that the incertitude on the temperature measurements is of 
±0.003°C.
The solid line represents the 5th order polynomial adjustment applied to 
the CTD temperature measurements.

PROBE N°2782

The calibration results for the N°2782 probe are presented on figure 5b. 
Between the pre- and post-calibration the temperature sensor presents a 
drift of:

  • 0.002°C in average
  • 0.005°C at a temperature of 5°C (maximum)
  • 0.000°C at a temperature of 10°C (minimum).

    We considered that the incertitude on the temperature measurements is 
    of ±0.001°C.

    The solid line represents the 5th order polynomial adjustment applied 
    to the CTD temperature measurements.

The CTD temperature has been compared to SIS reversing thermometer 
measurements. The SIS thermometers have been calibrated  before and after 
the cruise, at  the same dates than the CTD temperature sensor. The figures 
6 show the temperature difference between the SIS and CTD measurements. The 
SIS and CTD temperature data  have been calibrated before the comparison. 
The figures 6 show that there is a bias between the two types of 
measurements: a bias of +0.017°C for the N°T_216 thermometer and +0.007°C 
for the N°T_707 thermometer. The laboratory calibrations point out an 
important drift at the 0°C temperature reference (+0.025°C for the N°T-216 
thermometer and +0.015°C for the T_707 thermometer) for the SIS 
thermometers. The observed bias was constant during the whole cruise, and 
does not depend on the probe we used. We are thus confident in the probe 
measurements and we attributed the observed bias to the SIS thermometer 
measurements.

PRESSURE CALIBRATION

The pressure sensor of the CTD was calibrated before and after the cruise.
The N°2756 probe has been calibrated on December 15, 1995, and on October 
30, 1996.

The N°2782 probe has been calibrated on December 6, 1995, and on October 1, 
1996.

In order to estimate the hysteresis of the pressure sensor, laboratory 
calibration have been performed:
 1 – for increasing pressure (down casts)
 2 – for decreasing pressure (up casts)

PROBE N°2756 (Figure 7)

The pressure sensor did not drift a lot during the 6-months interval (less 
than 2 dbar)  and the difference between the pre-calibration and post-
calibration is constant at every depth (Figure 7). We fitted the results of 
the calibration with a 5 order polynomial curve.

The CTD down-cast pressure measurements are calibrated by using the 
coefficients obtained in the laboratory for increasing pressure, at a 
temperature of 20°C. For the up casts we used the calibration coefficients 
obtained in the laboratory for decreasing pressure, at a temperature of 
15°C. This was an arbitrary choice, as we had no means to know the 
temperature of the pressure CTD sensor. The use of two different reference 
temperatures, for the up- and down-cast calibration, induced different 
pressure values at 6000 m (Figure 7). The discrepancy is negligible at 
5000 m, the maximum depth of the measurements.

PROBE N°2782 (Figure 8)

The calibration coefficient of the N°2782 probe have been computed by 
A.Billant of the Laboratoire d’Océanographie Physique of the IFREMER center 
in Brest. 

For the shallow casts (depth < 500 m) we used only the calibration 
coefficients obtained for increasing pressure, estimating that the 
hysteresis is negligible. 

The pressure measured by the CTD can be compared to the SIS digital 
reversing pressure meters. The SIS have been calibrated in the laboratory 
before and after the cruise at the same date than the CTD pressure sensor. 
The calibration has been made at a temperature of 2°C close to the 
temperature at which they were used. The figures 9 present the pressure 
difference between the SIS and CTD  measurements after calibration. The 
comparisons show that the SIS corrected pressure and CTD corrected pressure 
are equal with an incertitude of 5 dbar. 

SALINITY CALIBRATION

The calibration of the CTD conductivity sensor is made by comparing the CTD 
conductivity measurements, at the depth where the bottles are closed, to 
the in-situ conductivity of the water samples. The CTD conductivity 
measurements are corrected from the temperature and pressure effect on the 
conductivity cell. The CTD conductivity measurements are calibrated using a 
linear regression. The polynomial coefficients are computed iteratively.

IMPORTANT

The rosette was not equipped with a non-data interrupt rosette firing 
module. Due to this deficiency, the conductivity measurements were 
perturbed during the up-cast profile. We judged the perturbation 
sufficiently important to modify the normal calibration procedure: to find 
the calibration coefficients, we compared the water sample conductivity to 
the CTD conductivity measurements of the DOWN-cast instead of the UP-cast. 
We used the pressure of the up-cast water sample to find the CTD 
conductivity in the down-cast profile. This method is similar to that used 
for the calibration of the oxygen sensor. That procedure gave correct 
results, but has the disadvantage of eliminating an important number of 
water samples between the surface and 1500 dbar.

CALIBRATION

Note that:

  • the CTD n°2756 has been used for stations N°1 to N°9 and for stations 
    N°65 to N°95 
  • CTD conductivity are unusable below 2580 dbar for the station N°8.
  • CTD conductivity are unusable below 1500 dbar for the station N°9.
  • CTD conductivity profiles of station N°10, N°11, N°12, N°13 are 
    unusable.
  • The CTD conductivity sensor has been cleaned before stations N°20, 
    N°36, n°49, n°65, n°80.  
  • The stations made in shallow water (bottom < 1500 m) are : N°1, N°2, 
    N°3, N°4, N°5, N°63, N°64, N°65, N°66, N°94, N°95.


TABLE 9. Calibration coefficient for the CTD conductivity sensor

     _________________________________________________________________
      
      Stations  Number   Number of  Standard
                of used  retained   deviation      Coefficients
                samples  samples    (0–6000 m)     C1        C2
      --------  -------  ---------  ----------  --------  --------
       1 -> 7      75       59        0.0085    1.000496  -0.02704
       8           19       19        0.0121    1.000926  -0.03716
      14 -> 19    129       94        0.0023    0.999995  -0.00495
      20           22       20        0.0037    0.999848  -0.00924
      21 -> 22     56       51        0.0028    0.999738  -0.00472
      23           28       23        0.0014    0.999909  -0.01206
      24           28       26        0.0052    0.999938  -0.01093
      25 -> 27     78       59        0.0024    0.999903  -0.01145
      28 -> 29     56       38        0.0014    0.999920  -0.00792
      30           28       24        0.0038    0.999940  -0.01248
      31           22       21        0.0044    1.000356  -0.02149
      33           27       26        0.0023    0.999975  -0.01149
      34           28       26        0.0037    0.999534   0.00674
      35 -> 37     70       57        0.0040    0.999981  -0.01047
      38 -> 44    128       94        0.0022    0.999910  -0.01056
      45 -> 46     44       38        0.0045    0.999969  -0.01034
      47 -> 48     44       36        0.0032    0.999912  -0.01009
      49 -> 56    216      178        0.0023    0.999624  -0.01279
      57 -> 64    153      114        0.0029    0.999248   0.01352
      65 -> 71    118       86        0.0026    1.004005  -0.01560
      73 -> 77    108       81        0.0019    0.999951  -0.01345
      78 -> 94    355      266        0.0022    0.999925  -0.01986
     _________________________________________________________________


2043 water samples have been taken out during the cruise. Eliminating the 
samples of the test stations N°32, N°42, N°72, and N°87, of stations N°9, 
N°10, N°11, N°12, and N°13 as well as the bad measurements, we retained 
1832 water samples for the calibration. 1436 comparisons have been retained 
by the minimization process (78.2% of the measurements).

The figure 10 shows the resulting conductivity difference after the 
calibration procedure.

The difference is lower than 0.001 mmho cm^-1 for 17% of the samples.
The difference is lower than 0.003 mmho cm^-1 for 50% of the samples.

CONTROL

To control the quality of the calibration, θ-S diagrams have been 
compared:

(1) Between successive stations of the cruise.
(2) Between stations made at the same position during the cruise (N°26 and 
    N°84).
(3) Between different cruises.


(1) θ-S diagrams of consecutive stations made during the cruise have been 
    systematically compared. The differences (>= 0.0005), for potential 
    temperature lower than 1.9°C, have been systematically reported in the 
    following table. The difference is positive when the station in the 
    first column has a salinity greater than the station in the second 
    column. 


TABLE 10. Salinity comparison between contiguous profiles of the ETAMBOT 2
          cruise

                ____________________________________________
                
                   ETAMBOT 2       ETAMBOT 2      Salinity
                 Station Number  Station Number  Difference
                 --------------  --------------  ----------
                       14              15          0.0020
                       15              16         -0.0020
                       16              17          0.0015
                       17              18         -0.0010
                       20              21          0.0015
                       34              35          0.0010
                       47              48         -0.0020
                       48              49          0.0020
                       57              58         -0.0010
                       58              59          0.0020
                       73              74         -0.0020
                       75              76          0.0010
                ____________________________________________


The comparison is satisfactory. Only 8 comparisons show a difference 
greater then 0.0010. No correction have been made to these salinity 
profiles.

(2) During the ETAMBOT 2 cruise, 9 stations have been made at the same 
    geographical position, but only the stations N°26 and N°84 (41°20’W-
    7°30’N) are sufficiently deep to allow a meaningful comparison. The 
    comparison is reported on Figure 11. On the θ-S diagrams the salinity 
    difference, for a given temperature, does not exceed 0.0010, below the 
    potential temperature 1.9°C.

(3) The ETAMBOT 2 cruise exactly repeats the cruise track of the ETAMBOT1 
    cruise and the western part of the CITHER 1 cruise (WHP A6 and A7 
    lines). 

Omitting the shallow stations, 80 θ-S diagrams of the ETAMBOT1 and 
ETAMBOT2 cruises have been compared. The differences, for potential 
temperature lower than 1.9°C, have been systematically reported in the 
following table. The difference is positive when the station in the first 
column has a salinity greater than the station in the second column. 


TABLE 11. Salinity comparison between ETAMBOT 1 and ETAMBOT 2 profiles

                ____________________________________________
                
                   ETAMBOT 2       ETAMBOT 2      Salinity
                 Station Number  Station Number  Difference
                 --------------  --------------  ----------
                       15              15         -0.0020
                       20              20          0.0010
                       24              24         -0.0010
                       33              33          0.0010
                       36              36          0.0010
                       43              42         -0.0020
                       49              48         -0.0010
                       51              50          0.0010
                       69              68          0.0020
                       73              71          0.0010
                       74              72          0.0020
                       75              73          0.0010
                       86              84         -0.0020
                ____________________________________________


Likewise 40 θ-S diagrams of the ETAMBOT 2 and CITHER 1 cruise have been 
compared. The salinity differences are reported in the following table. 


TABLE 12. Salinity comparison between ETAMBOT 2 and CITHER 1 profiles

                ____________________________________________
                 
                   ETAMBOT2         CITHER1       Salinity
                 Station Number  Station Number  Difference
                 --------------  --------------  ----------
                       15              133        -0.0030
                       19              137        -0.0010 
                       20              138         0.0010
                       33              151         0.0020
                       34              153         0.0010
                       43              114        -0.0010
                       48              110         0.0010
                       52              106         0.0010
                ____________________________________________
                
                
The difference observed at the ETAMBOT2 station N°15 has not been 
corrected.

OXYGEN CALIBRATION

CTD oxygen were calibrated by fitting to sample values using the method 
described in Owens and Millard [1985].

During the cruise the oxygen sensor worked for stations N°14 to N°22, N°29 
to N°36 using the N°2782 probe, and for stations N°1 to N°8, N°65 to N°95 
using the N°2756 probe. Furthermore several oxygen profiles are noisy. All 
these profiles have been calibrated but they must be used with cautious. 

1041 samples have been used to calibrate the data. 966 samples (92.7%) have 
been retained during the fitting process. The following Table shows the 
results of the calibration:


TABLE 13. Calibration results for the oxygen sensor

              ____________________________________________
              
                                              Standard
                         Number   Number of   deviation
               Station   of used  retained   (0 – 5000 m)
               Number    samples  samples     μmol kg^-1
               --------  -------  ---------  ------------
                1 ->  8     94       92          3.0
               14 -> 22     20      181          1.5
               29           28       28          2.9
               30           28       28          2.8
               31           22       22          1.6
               33           28       26          0.8
               34           28       27          1.6
               36           22       20          1.9
               65 -> 71    118      111          1.6
               73 -> 86    347      322          1.8
               88 -> 94    119      109          1.5
              ____________________________________________


The figures 12 show the differences, in µmol kg^-1, between the oxygen 
samples and the down-cast CTD measurements.

   The difference is lower than 1 µmol kg^-1 for 27% of the samples .
   The difference is lower than 2 µmol kg^-1 for 65% of the samples .

CONTROL

As for the salinity profiles, the comparison with the oxygen profiles of 
the ETAMBOT1 have been made. 


TABLE 14: Oxygen comparison between ETAMBOT 1 and ETAMBOT 2 profiles

            _________________________________________________
            
             N° de station  N° de station  Oxygen difference
               ETAMBOT 2      ETAMBOT 1       μmol kg^-1
             -------------  -------------  -----------------
                  14             14             -2.0
                  19             19             -1.0
                  20             20             -1.0
                  30             31             -1.0
                  73             71             -1.0
                  80             78             -1.0
            _________________________________________________

NOTE

The CTD oxygen profiles have not been de-spiked. Some profiles show 
important spikes in the upper thermocline.
The CTD oxygen profiles have not been filtered. 


ACKNOWLEDGEMENTS

This project has been supported by ORSTOM as part of the Programme National 
d’Etude de la Dynamique du Climat, and its WOCE/France subprogramme.



Figure captions

Figure 1:  Cruise track and station position.
Figure 2:  Oxygen versus salinity for ETAMBOT 2 and historical data (SAVE 
           Leg 6 [35°W, 1°N to 1°S], and TTO-TAS [45°W-1°N to 41°W-7°30’N]). 
Figure 3:  Nitrate – phosphate correlation for ETAMBOT 2 cruise data.
Figure 4:  Silicate versus temperature for ETAMBOT 2 and historical data 
           (SAVE Leg 6 [35°W, 1°N to 1°S] and TTO-TAS [45°W-1°N to 41°W-7°30’N]).
Figure 5:  Temperature difference , in °C, between the laboratory reference 
           temperature and the temperature measured by the probe. The solid 
           represent the 5th order polynomial minimizing the differences. 
           Calibration results for the N°2756 CTD probe calibration results 
           for the N°2782 CTD probe
Figure 6:  Temperature difference, in °C, between SIS and CTD measurements 
           (after calibration).
Figure 7:  Pressure difference, in dbar, between the laboratory reference 
           pressure and the pressure measured by the N°2756 probe. The solid 
           represent the 5th order polynomial minimizing the differences. 
           a) calibration for increasing pressure at a 20°C temperature (down cast).
           b) calibration for decreasing pressure at a 15°C temperature (up cast).
Figure 8:  Calibration curve for the pressure sensor of the N°2782 CTD probe 
           a) calibration for increasing pressure (down cast).
           b) calibration for decreasing pressure (up cast).
Figure 9:  Pressure difference, in dbar, between SIS and CTD measurements 
           (after calibration). 
Figure 10: Conductivity difference, in mmho/cm, between water sample and 
           CTD measurements, after calibration.
           a) difference as a function of station number.
           b) difference as a function of pressure.
Figure 11: θ-S diagram of repeated ETAMBOT 2 stations N°26 and N°84 
           (41°40’W-7°30’N).
Figure 12: Dissolved oxygen difference, in μmol kg-1, between water sample 
           and CTD measurements.
           a) difference as a function of station number.
           b) difference as a function of pressure.



WHPO DATA PROCESSING NOTES

Date      Contact     Data Type          Event Summary
--------  ----------  -----------------  ------------------------------------
04/23/98  Gouriou     Cruise Report      Submitted (hard copy)

04/28/98  Gouriou     CTD/BTL/SUM        Submitted for DQE

03/10/99  Bartolacci  CTD/BTL/SUM*       Website Updated

02/14/00  Gouriou     CTD/BTL/SUM        Status changed to Public

06/02/00  Huynh       Cruise Report      pdf, txt versions online, 

08/04/00  Huynh       Cruise Report      new pdf w/ figs online

01/01/08  Bartolacci  BTL/Cruise Report  Small edits made
          It was brought to our attention by a user that the station 42 of 
          the bottle file for ar04_hhy.txt was missing the column of values 
          for FCO2.  PH and QUALT1 columns were shifted over.  QUALT1 column 
          was missing quality byte for this column as well.
          • Added -9.0 values in the FCO2 column, and added a 5 quality byte 
            (not  reported) to the QUALT1 column.
          • Added place holding zeros to all leading decimal values (eg. .07 
            to 0.07).
          • Added place holding zeros to all trailing decimal values (eg. 1. 
            to 1.0)
          • Realigned first three data columns and headers.
          • Realigned and corrected spelling of QUALT1 header. 
          • edited date/name stamp (previous stamp was: 20010323SIOUCSD this 
            is incorrect).
          • ran wocecvt with no errors.
          • replaced online version with newly edited file and RCS'd this action.

01/10/02  Bartolacci  BTL                Reformatted data online
          I have edited the file to correct the missalignment of the missing 
          station data and also the other columns as well.  There is a new 
          file for this cruise online now. My student and I are also working 
          on the others on your list you sent to Steve to see why they 
          haven't get gotten into exchange. 

          It's usually just minor reformatting that keeps these cruises in 
          the exchange queue.  Karla is going to investigate and generate the 
          easier exchange files.  I'll tackle any remaining ones, and we'll 
          keep you posted on our progress, or you can keep checking the 
          website for updated files.

            On Fri, 21 Dec 2001, Tom Haine wrote:
            Steve,
            I've been looking at the repeat .txt files. I think the FCO2 data 
            are missing from STNNBR 042 in ar04_hhy.txt. At least, there's 1 
            less column for this station.

01/11/02  Uribe      BTL                 Exchange file online
          Bottle file has been converted to exchange and put online.

03/04/02  Uribe      CTD                 Exchange file online
          CTD has been converted to exchange and put online.

04/10/02  Lebel      CFCs                Final CFC data submitted
          The file:  ar04h.dat - 305211 bytes has been saved as: 
            20020410.124051_LEBEL_AR04F_ar04h.dat in the directory:  
            20020410.124051_LEBEL_AR04F
          The data disposition is: Public
          The file format is:      Plain Text (ASCII)
          The archive type is:     NONE - Individual File
          The data type(s) is:     Other: final CFC data
          The file contains these water sample identifiers:
               Cast Number    (CASTNO)
               Station Number (STATNO)
               Bottle Number  (BTLNBR)
               Sample Number  (SAMPNO)
          LEBEL, DEBORAH would like the following action(s) taken on the data:
               Merge Data
               Place Data Online
               Update Parameters
          Any additional notes are:
          These are the finalized CFC data for Etambot2 (AR04H). Scale is 
          SIO98, units are pmol/kg.  Includes QUALT2 word.

07/23/02  Buck        CTD                Expocode edited to reflect HYD
          Changed expocode in CTD file from 35LKETAMBOT2 to 33LKETAMBOT2 to 
          match SUM file and HYD file.

02/10/03  Bartolacci  CTD                lat/lon inconsistent
          For some time now we have been trying to clean up the last of the 
          repeat cruises and incorporating current meter cruise data has 
          fallen into this category. We were forwarded CTD data and two email 
          correspondences by Jim Crease for the KN04 cruise.

          I am working on formatting these CTD files into a WOCE CTD format 
          and a summary file.  I am having some difficulties with the 
          inconsistant lat/lon values recorded in the files. The values in 
          the files that we obtained are are of differring precision and in 
          some cases exceed any possible lat/lon value.

          Can you please help?  We have no cruise or data documentation for 
          these files and presently do not even know who the Chief Scientist 
          was on cruise!  Could you please forward a data contact with whom I 
          might correspond to regarding these matters?  We would like to 
          button this up as soon as possible and any information you could 
          give us would be greatly appreciated.


      

WOCE AR15, AR04W and AR04E, R/V EDWIN LINK, Cruise ETAMBOT 2              


