Dutch JGOFS - Dissolved oxygen measured during the North Atlantic Pilot Project (Leg 1)

The North Atlantic Pilot Project (NAPP), also known as the North
Atlantic Bloom Experiment (NABE), was the first field work of JGOFS
(Joint Global Ocean Flux Study) and it served as pilot study for the
proposed North Atlantic Process Study. Six countries participated in
this study: Canada, France, Germany, The Netherlands, UK and USA

The Netherlands contributed to NAPP with four cruises on board
R.V. Tyro:
1. Leg 1, 31 July-11 September 1989 (Upper Ocean Processes)
2. Leg 2, 13-28 September 1989 (Benthic Processes)
3. Leg 3, 17 April-31 May 1990 (Upper Ocean Processes)
4. Leg 4, 2-29 June 1990 (Benthic Processes)

The following oxygen data set originated during Leg 1. Over 900
oxygen samples were collected as duplicates at 39 stations, using
the rosettesampler/CTD and Niskin bottles and analyzed according to
a High Precision Winkler Titration Method (Tijseen 1980, Tijseen and
van Bennekom 1989). At most stations from 2 or 3 depths and at 2
stations from all (=12) depths, simultaneously sewater blanks have
been taken and analyzed. From 60N to 33N the blanks tend to be lower,
while values at 10 m always are lower than values beneath 500 m. The
mean blank value is 0.7 micromol/kg.
After sampling, reagents A and B have been added immediately, while in
a third bottle the "sample temperature" has been measured. Differences
between T-in situ and T-sample appear to be much smaller as was expected.
Deep samples were supplied with reagents in a shelter on deck, at air
temperature is over 25 degrees Celsius, differences are smaller than
5 degrees Celsius. Before starting each titration the temperature of the
0.2 N thiosulphate solution has been measured. To control the titer of
the thiosulphate solution (0.17070 precisely) in the beginning of the
cruise, 24 samples had been taken out of 1 Niskin bottle and during the
cruise ever fifth day 2 samples have been titrated. This control shows
non-systematic small differences within 1 micromol/kg. Data are corrected
for titration temperature and seawater blanks. Correction for sample
temperature was also applied. The calculated value in micromol/liter at
T-sample was divided by the density (at T-sample and given salinity) as to
arrive at the reported micromol/kg. Differences between the mean values of
duplicate samples generally are smaller than 0.2 micromol/kg, which is in
accordance with the JGOFS criteria. On August the 6th 1989 an intercalibra-
tion program, on which also oxygen titration was involved, between German,
English and Dutch participants on JGOFS 1, took place.

Tijssen,S.B. (1981). Anmerkungen zur photometrisched Winkler.
Sauerstofftitration und ihre Anwendung zur Schatzung der Primarproduktion
im Meer. In: III Internationales mikorbiologisches Symposium, Smolenice,
3-6 Juni 1980. Editor L. Daubner. Veda, Verlag der Slowakischen Akademie
der Wissenschafter, Bratislava 1981.

Tijssen, S.B. and A. J. van Bennekom (1989). High precision determination
of dissolved oxygen. ICES Report CM 1989/C:6