6
METHODS (since 1978)
Water samples were taken at various depths using plastic Nansen bottles (Hydrobios, Kiel) or a rosette
sampler with Niskin bottles (General Oceanics, Miami). The salinity of the samples was measured
using an inductive salinometer, since 1982 an Autosal-salinometer.
The following nutrient analyses were carried out on board using a filterphotometer (Elko II, Carl
Zeiss, Oberkochen):
Dissolved inorganic phosphate according to Murphy and Riley (1962); precision (95% confidence
range): ±0.03 pmol/l. Ammonia nitrogen according to Koroleff (1983); precision (95% confidence
range): ±8%. Nitrite nitrogen according to Grasshoff (1983); precision (95% confidence range): +0.02
gmol/1.
Samples of silicate, nitrate+nitrite, total nitrogen, total phosphate and, from January 1990, also of
dissolved inorganic phosphate were deep-frozen and analysed immediately on return: Silicate and
nitrate+nitrite in the autoanalyzer in line with Technikon's instructions (1972); total nitrogen after
oxidation in an alkaline medium; precision (95% confidence range): ±0.3 pmol/1 for silicate, ±0.5 gmol/
1 for nitrate+nitrite, ±7% for total nitrogen. Up to 1989, total phosphate was determined photometrically
after digestion with potassium peroxodisulphate according to Koroleff (1968); precision (95% confiden
ce range): ±0.05 pmol/1. After January 1990, total phosphate, like dissolved phosphate, was determined
in the autoanalyzer according to Mangelsdorf (1972); precision (95% confidence range): ±3%.
The phosphate, silicate, nitrite and nitrate+nitrite samples were filtered before analysis or deep
freezing. The total phosphate and total nitrogen samples were filtered after digestion. To prevent
contamination, the ammonium samples were not filtered. Instead, their turbidity blanks were measu
red as part of the photometric analysis and subtracted from the results. The same procedure was
applied to the 1978 samples for phosphate.
The samples analysed in 1936 were filtered as described above. Weichart (1990) examined the
comparability of the old phosphate data with the new.
