RV Pelagia Shipboard Report:

Cruise 64PE110, Project TripleB,

WHP repeat area AR12

H.M. van Aken
Chief Scientist

Bay of Biscay Boundary
NIOZ, Texel, 1997

The research reported here was 
funded by the Foundation for 
Geological, Oceanographic and 
Atmospheric Research (GOA), 
subsidiary of the Netherlands 
Organization for Scientific Research 
(NWO), contract no. 750.197.01 .

1 	Cruise Narrative

1.1	Highlights

a:	WOCE Repeat Area AR12, RV Pelagia cruise PE110 in the 
	Bay of Biscay

b:	Expedition Designation (EXPOCODE): 64PE110

c:	Chief Scientist:	Dr. Hendrik M. van Aken
	Netherlands Institute for Sea Research (NIOZ)
	P.O.Box 59
	1790AB Den Burg/Texel
	The Netherlands
	Telephone:	31(0)222-369416
	Telefax:		31(0)222-319674
	e-mail:		aken@nioz.nl

d:	Ship: RV Pelagia,	Call Sign:  PGRQ
				length 66 m.
				beam 12.8 m
				draft 4 m
				maximum speed 12.5 knots

e:	Ports of Call:  	Texel (the Netherlands) to 
				Texel (the Netherlands)

f:	Cruise dates:  	August 8, 1997 to August 29, 1997

1.2	Cruise Summary Information

Summary

Early before noon of 8 August RV Pelagia left port in Texel, and 
headed for the Bay of Biscay. At 10 August a CTD test station was 
performed. We arrived at the Biscay continental slope near 
mooring BB13 late that day, and spent the night carrying out a 
echo sounder survey over the slope. The following day moorings 
BB17 to BB20 were recovered, and course was set to mooring 
BB10. On 12 August, after a nightly echo sounder survey, 
moorings BB10 to BB12 were recovered, and a CTD cast near 
mooring 12 was performed. On 13 and 14 August a CTD section 
from 46N towards the continental slope near Gijn was surveyed 
(section A). On 15 August, after a nightly echo sounder survey, 
moorings BB21 to BB24 were deployed. Hereafter course was set 
to the Meriadzek Plateau, were on 17 August moorings BB17 to 
BB20 were deployed. Then RV Pelagia headed to the area west of 
Finisterre where late in the evening of 18 August the CTD survey 
of  section B was started. After finishing section B, sections C, D, 
and E were surveyed in order to fill in geographical data gap in the 
surveys of the preceding years. Finally sections F and G across 
the French continental slope were surveyed; a re-survey of 
sections, from which hydrographic measurements were obtained 
in 1993, 1995, and 1996. During the hydrographic survey a total of 
5 ARGOS surface drifters was deployed. At Tuesday 26 August 
the observations in the Bay of Biscay were ended, and RV Pelagia 
arrived back in Texel on Friday 29 August.

Cruise Track

The cruise was carried out in the Bay of Biscay and west of NW 
Spain east of 12_30'W. The cruise track is shown in figure 1.

 

Figure 1.	Cruise track of RV Pelagia cruise 64PE110

Number of Hydrographic Stations

A total of 64 CTD casts was recorded. On 55 of these casts, water 
samples were taken for the determinations of salinity and 
dissolved oxygen. Three water samplers in the rosette system 
were fitted with reversing electronic thermometers and pressure 
sensors. The positions of the hydrographic stations is indicated in 
figure 2.

At the hydrographic stations the SBE9/11+ CTD was lowered with 
a speed of about 1 m/s. Due  to the use of a bottom indicator 
switch we were able to sample to within quite a short distance 
from the bottom (5 m).

 

Figure 2.	Distribution of hydrographic stations and sections.

Hydrographic Sampling

During the up-cast of each CTD/rosette station water up to 13 
samples were taken at regular depth intervals. The samples were 
analysed for salinity. Only on sections B and F also the dissolved 
oxygen content of the samples was determined. Three water 
samplers were fitted with reversing electronic thermometers and 
pressure sensors.

The vertical distribution of the sampling locations is indicated in 
figure 3.

 

Figure 3.	Vertical distribution of the water samples versus station 
number.

Moorings

The moorings BB10 to BB16, deployed in 1996, were recovered 
without problems. Two Aanderaa RCM 8 current meters had 
leaked and contained only about a week of data. All other 
Aanderaa current meters contained at least over a year of data. 
The NBA current meters, as expected, all had encountered battery 
failure after about 6 months, which caused the data recording to 
stop. One NBA current meter showed a bit error in the direction. 
This effectively reduced the resolution of the current direction to 22 
degrees.

After recovery of the current meters, their data were read and 
copied to the computer network of RV Pelagia. The data were pre-
processed, and corrected for the magnetic variation. From the pre-
processed data a low-pass data set, sub-sampled every 12 hours, 
as well as a high-pass data set, sub-sampled every hour were 
produced.

After servicing the current meters, moorings BB17 to BB24 were 
deployed, BB17 to BB20 over the continental slope near the 
Meriadzek Plateau, moorings BB21 to BB24 over the continental 
slope north-west of Gijn.

ARGOS drifters

During the cruise five ARGOS drifters were deployed. The drifters 
used were standard spherical WOCE/TOGA mixed layer drifters 
(diameter 30 cm), fitted with a holey sock drogue at 15 m. The 
drogues had a length of 7 m, and a diameter of 1 m. The ARGOS 
ptt numbers of the drifters are 12416 to 12420.

The positions of the drifter and mooring deployments are indicated 
in figure 4.

 

Figure 4.	Positions of moorings and drifter deployments.

*.SUM file

The preliminary 64PE110.SUM file describing all stations has 
been submitted to WHPO.

1.3	List of Principal Investigators

Name			Responsibility				Affiliation

Dr. H.M. van Aken	Ocean hydrography, ARGOS drifters	NIOZ/Texel
Ing. S. Ober 	CTD & rosette-technology		NIOZ/Texel
Drs. C. Veth	Current measurements			NIOZ/Texel

1.4	Scientific Programme and Methods

The goal of the research carried out during the cruise was to 
establish the structure, course and transport of the eastern 
boundary current in the Bay of Biscay, as well as the hydrographic 
structure of the Bay of Biscay and the nearby eastern North 
Atlantic, as it is affected by the eastern boundary current. For this 
purpose a hydrographic survey has been carried out in the Bay of 
Biscay up to 12*30'W, eight long term current meter moorings and 
five ARGOS surface drifters have been deployed. Seven long term 
current meter moorings, deployed in 1996, were recovered. The 
hydrographic survey covers part of the WOCE Hydrographic 
Research Programme repeat area AR12, and complements the 
hydrographic surveys, carried out in 1995 and 1996 in the Bay of 
Biscay in the TripleB programme.

The CTD-rosette frame was weighted in order to secure a fast 
enough falling rate. This package was lowered with a velocity of 
about 1 m/s, except in the lowest 100 m, where the veering 
velocity was reduced. Measurements during the down-cast went 
on to within 5 m from the bottom, until the bottom switch indicated 
the proximity of the bottom. During the up-cast water samples 
where taken at prescribed depths, when the CTD winch was 
stopped. After each cast the CTD/rosette frame was placed on 
deck. Subsequently water samples were drawn for the 
determination of dissolved oxygen and salinity, and the readings of 
the reversing electronic thermometers and pressure sensor were 
recorded.

A secondary goal in the programme was the testing of a multi-
valve rosette system, developed at NIOZ, as well as the testing of 
newly acquired oxygen and transmissometer sensors, as well as 
newly acquired reversing electronic thermometers and pressure 
sensors.

Preliminary Results

At the end of the cruise the data are available in raw form, without 
final calibration and proper CTD processing. Oxygen is still in 
volumetric concentrations and should be transformed into 
densimetric concentrations and corrected for sea water blanks. 
However already from these raw data, presented in figures 5 to 7, 
some insight can be gained of the hydrographic situation in the 
Bay of Biscay during the cruise.

 

Figure 5.	Vertical distribution of potential temperature and 
salinity from all CTD casts, sub-sampled every 50 
dbar.

 

Figure 6.	Diagrams of salinity and potential vorticity versus 
potential temperature. The data are from all CTD casts, 
sub-sampled every 50 dbar.

 

Figure 7.	Plots of the dissolved oxygen concentration versus the 
pressure, and versus the potential temperature.

1.5	Major Problems Encountered during the Cruise

The newly developed multi-valve rosette system was tested on 
stations 1, 8, 9 and 10. Initially the system functioned quite well, 
but at pressures over 2000 dbar at station 8 the closing of the 
samplers failed, whereas at stations 9 and 10 the closing of the 
samplers was a complete failure. Thereupon it was decided to 
switch the CTD to the G.O. rosette rack. On later stations the 
multi-valve was also mounted in that rack in order to perform tests 
to find out what caused the problems. Slight modifications were 
made in the multi-valve, and at the end of the cruise the 
performance of the system was considered to be satisfactory.

Both the newly acquired oxygen sensor and transmissometer gave 
erroneous values. Contacts will be established with the 
manufactures in order to improve the sensors.

After recovery of moorings BB10 to BB16 it appeared that five of 
the radio beacons and flashlights, mounted on the beacon float 
had leaked. Only one could be repaired. It was decided to switch 
spare parts from the faulty flashlight to the faulty radio beacons, so 
that all moorings BB17 to BB24 could be fitted with at least a radio 
beacon.

During the deployment of mooring BB17 the ARGOS SMM 
transmitter in the frame on top of the ADCP was torn loose, and 
lost into the sea.

Halfway the cruise the shipboard computer TRITON had a disk 
crash. This computer acted as e-mail server, and because of its 
failure further e-mail contacts with the shore was inhibited. Also, 
because of this computer failure, direct access to the data from the 
continuous logging system was denied. Only after return to Texel, 
these data will be available.

The ITI temperature sensor in the ABC underway logging system 
showed erroneous values in is in need of repair. The 
meteorological sensors for air temperature, humidity and air 
pressure gave completely unreliable values and should be 
replaced.

1.6	Lists of Cruise Participants

Scientific crew

Person		Responsibility					Institute

H.M. van Aken	Chief Scientist, ARGOS 				NIOZ
			drifters, Data Management
J.P.J. Berkhout	Hydro Watch, Oxygen Determination		IMAU
J. Blom		Mooring Operations, Technical Assistance	NIOZ
R.L. Groenewegen	Computer Network, Acoustic Releases, 	NIOZ
			Electronics
M. Hiehle		Hydro-Watch, Salinity Determination, 	NIOZ
			Data Management
M.T.J. Hillebrand	Current meters, Hydro Watch			NIOZ
M. Manuels		Oxygen Determination, Current Meters	NIOZ
S. Ober		CTD system, Thermometry, ADCP			NIOZ
W. Polman		Mooring Operations, Technical Assistance	NIOZ
L. de Streur	Hydro-Watch, Salinity Determination		IMAU
G.M. Terra		Hydro-Watch, Salinity Determination		IMAU
E. Tuenter		Hydro-Watch, current meters			IMAU
C. Veth		Current Meters, Hydro Watch			NIOZ
M. Walgreen		Hydro-Watch, Salinity Determination		IMAU

	NIOZ:	Netherlands Institute for Sea Research, Texel
	IMAU:	Institute for Marine and Atmospheric Research, Utrecht 
		University

Ships crew
J. Groot		captain
M.D. van Duijn	first mate
P. van Erve		second mate
J. Seepma		first engineer
J. Kalf		second engineer
G. Steenhuizen	cook
P.-W. Saalmink	ships technician
R. van der Heide	ships technician
S. Kuiper		ships technician

2	Underway Measurements

2.1	Navigation

RV Pelagia has several different navigational systems. We used 
the Differential GPS receiver for the determination of the position. 
The data from this receiver were recorded every  ten seconds in 
the ABC data logging system. After removal of a few spikes these 
data were sub-sampled every  minute.

2.2	Echo Sounding

The 3.5 kHz echo sounder as well as the navigational Furuno 
echo sounder were used on board to determine the water depth. 
The uncorrected depths from these echo sounders were recorded 
in the ABC data logging system. Over the steepest parts of the 
continental slope the depth digitizer of the 3.5 KC echo sounder 
was occasionally not able to find a reliable depth. The maximum 
range of the Furuno echo sounder to obtain reliable results was 
about 800 m.

Near the positions of the recovered current meter moorings on the 
continental slope additional echo sounder surveys were carried 
out to determine the topography of the deployment locations. 
Preceding the deployment of the current meter moorings one 2 to 
5 lines were surveyed to determine the deployment sites, which 
were bound to pre-determined depth ranges.

2.3	Thermo-Salinograph Measurements

The Sea Surface Temperature, Salinity, and dissolved Oxygen 
concentration were measured continuously with an AQUAFLOW 
thermo-salinograph with the water intake at a depth of about 3 m. 
The primary temperature sensor, mounted near the water inlet, 
showed an increasing unreliable behaviour during the cruise. From 
data from the first five days however it appeared that the 
secondary thermometer in the AQUAFLOW system gave 
temperatures within 0.1C of the temperature from the primary 
sensor. For the calibration of the salinity sensor and the oxygen 
sensor, water samples were taken three times per day.

3	Hydrographic measurements - Descriptions, Techniques, and Calibrations

3.1	Rosette Sampler and Sampler Bottles

A General Oceanics 24 position rosette sampler was used, fitted 
with 10 litre NOEX sampler bottles. On most stations only 13 
sampler bottles were placed in the rosette. Their general 
behaviour was good, but the samplers fitted with reversing 
electronic thermometers and pressure sensors (2, 4, and 6) quite 
often showed unreliable salinities. This occurred probably because 
of too early closing due to the vibrations of the thermometer cases, 
which caused the valves of the closing system to open 
prematurely. No errors in the functioning of the rosette sampler 
itself could be detected. The samplers from which oxygen samples 
were drawn were mostly fitted with silicon rubber lids. Oxygen 
samples from these bottles have to be corrected according to the 
algorithm determined during cruise 64PE95N/1, but such 
corrections are small, less than 1 _mol/kg. For test purposes, 
during a number of stations also sampler were taken with 
samplers, closed by means of the multi-valve unit. These samples 
are included in the present version of the *.SUM file, but later 
inspection of the data may lead to the omission of these samples 
in further reports.

3.2	Temperature Measurements

On sampler bottles 2, 4, and 6 thermometer racks were mounted, 
fitted with SIS reversing electronic thermometers with a numerical 
resolution of 1 mK. After the cruise calibrations of the SIS sensors 
at the water triple point as well as at a number of other 
temperatures in the intermediate and deep water temperature 
range will be carried out.

Also mounted on the CTD was a secondary SBE temperature 
sensor, but not connected to the sensor flushing system, as well 
as a high precision SBE35 temperature sensor. Preliminary results 
of comparison of the primary CTD temperature sensor with the 
secondary temperature sensor as well as with the SIS sensors 
and the SBE35 sensor indicate that the temperatures, measured 
with the different sensors, showed a strong agreement. For the 
samples with a temperature below 3.0C the difference between 
the temperature measured with the SBE35 and with the primary 
CTD sensor had an average of -0.1 mK and a standard deviation 
of 0.9 mK (N=47).

3.3	Pressure Measurements

In the thermometer racks, mounted on sampler bottles, also SIS 
reversing electronic pressure sensors were placed. Before the 
cruise these sensors were calibrated by the manufacturer. Also 
readings of the deck pressure was performed with the SIS sensors 
to determine the zero offset. Previous experience has shown that 
such offset readings before and after each CTD cast give identical 
results.

3.4	Salinity Measurements

Water was drawn from the samplers into a 0.5 litre glass sample 
bottle for the salinity determination after 3 times rinsing. The 
sample bottles had a massive rubber stopper as well as a screw 
lid. Salinity of water samples (SALNTY) was determined by means 
of an Guildline Autosal 8400A salinometer. The salinometer was 
used in a laboratory container, fitted with an air conditioning 
system. This kept the surrounding air temperature constant within 
1C. The readings of the instrument were performed by computer, 
giving the average and statistics of 10 consecutive readings. For 
each sample 3 salinity determinations were carried out. The 
standard water used was from batch P131 with a K15 ratio of 
0.99986 (S=34.994), prepared at 10 October 1996.

From each deep CTD/rosette cast an extra duplicate sample was 
drawn. Salinity determinations from the duplicate samples 
obtained from independent runs were used to determine the 
reproducibility of the salinity determination. The RMS value of the 
difference between duplicate water samples amounted to 0.0005 
salinity units.

The results from the water sample salinities will be used to 
determine the calibration of the CTD conductivity sensor. It was 
known beforehand that the conductivity sensor hat a slight 
calibration offset because of some fouling. A preliminary analysis 
of the difference between the water sample salinity and the CTD 
salinity sampled below 1000 dbar gives a mean value of -0.0041 
and a standard deviation of 0.0013 (N=216).

3.5	Oxygen Measurements

For the oxygen determination water samples were drawn in 
volume calibrated 120 ml pyrex glass bottles. Before drawing the 
sample each bottle was flushed with at least 3 times its volume. 
When the samples were drawn the temperature of the sample was 
determined. The determination of the volumetric dissolved oxygen 
concentration of water samples was carried out by means of a 
high precision automated oxygen Winkler titration system, based 
on an optical end point determination. The stock solution of KJO3 
used in the analysis was prepared and calibrated in the laboratory 
by using gravimetric methods. The stock solutions were stored at 
low temperature (~4_C). Final calibration of the 0.2 Mol Na2S2O3 
titrant on board took place by tritration of at least 6 samples of 
stock solution samples of 3 different concentration levels with the 
0.2 Mol titrant.

At each cast where samples for the oxygen determination were 
drawn, duplicate samples and samples for the determination of the 
sea water blank value were drawn from the deepest water 
sampler, and occasionnally from the shallowest sampler too. The 
resulting RMS of the difference between samples drawn from the 
same sampler amounted to 0.3 _mol/dm3.

3.6	CTD Data Collection and Processing

For the data collection the Seasave software, produced by SBE, 
was used. The CTD data were recorded with a frequency of 24 
data cycles per second. After each CTD cast the data were copied 
to a hard disk of the ship's computer network, and a daily back-up 
copy was made on tape. Back on Texel these data are 
downloaded into the NIOZ computer network, via the network 
connection in the harbour.

On board the up-cast data files were sub-sampled to produce files 
with CTD data corresponding to each water sample, taken with the 
rosette sampler. On board the CTD data were processed with the 
preliminary calibration data, and reduced to 1 dbar average ASCII 
files, which were used for the preliminary analysis of the data. Full 
re-calibration and data processing will be carried out at NIOZ, 
Texel.

4	Acknowledgements

The research reported here was funded by the Foundation for 
Geological, Oceanographic and Atmospheric Research (GOA), 
subsidiary of the Netherlands Organisation for Scientific Research 
(NWO), contract no. 750.197.01 .

We thank the ships crew and the personnel of the supporting 
technical departments of NIOZ for their professional support and 
active participation in the preparation and execution of the TripleB 
programme, especially for the cruise reported here.