Search the data

Dissolved nutrient data measured from the Netherlands GEOTRACES section GA04

Responsible investigator

Dr Micha J A Rijkenberg
email: Micha.Rijkenberg@nioz.nl
Royal Netherlands Institute for Sea Research (NIOZ)
P.O. Box 59 1790 AB Den Burg
The Netherlands

Dr Jan van Ooijen
email: jan.van.ooijen@nioz.nl
Royal Netherlands Institute for Sea Research (NIOZ)
P.O. Box 59 1790 AB Den Burg
The Netherlands

Data contributor

For cruise leg PE370 and PE373

Dr Jan van Ooijen
email: jan.van.ooijen@nioz.nl
Royal Netherlands Institute for Sea Research (NIOZ)
P.O. Box 59 1790 AB Den Burg
The Netherlands

For cruise leg PE373

Dr Sharyn Ossebaar
email: sharyn.ossebaar@nioz.nl
Royal Netherlands Institute for Sea Research (NIOZ)
P.O. Box 59 1790 AB Den Burg
The Netherlands

For cruise leg PE374

Mr Karel Bakker
email: karel.bakker@nioz.nl
Royal Netherlands Institute for Sea Research (NIOZ)
P.O. Box 59 1790 AB Den Burg
The Netherlands

Laboratory of analysis

Royal Netherlands Institute for Sea Research (NIOZ)

Dataset brief description

Dissolved nutrient data from GEOTRACES section GA04 (cruises PE370, PE373, PE374)

Dataset description

Dissolved nutrient (phosphate, silicate, nitrate and nitrite) concentrations from 140 full depth CTD casts on the GEOTRACES GA04 section cruises on the R/V Pelagia (PE370, PE373, PE374). Dissolved ammonium and hydrogen sulphide from PE373.

Acquisition description

Sampling methodology

Samples were obtained from a CTD 25L sampler with 24 bottles each 25 litres, and an UC CTD with 24 bottles each 24 litres.). All samples were collected in 125 ml polypropylene bottles and sub sampled unfiltered in the lab container for nutrients in 5 ml polyethylene vials. In the Black Sea (PE373), the oxic and anoxic samples were collected in 60 ml high-density polyethylene syringes with a three way valve to make it possible to sample air free water from the Niskin bottles of the Rosette. The syringes with a three way valve were first rinsed three times with a small amount of the sample taken directly from either the Ultra-clean or the normal CTD-rosette bottles before being completely filled.

After sampling on deck, the samples were processed in the lab. Samples were filtered through 0.2 µm filters and immediately sub-sampled:
For hydrogen sulphide in a glass vial containing 40 µl of 1N NaOH to keep samples in the S ₂ ^- form under alkaline conditions (PE373 only).
For ammonium (PE373 only), nitrate and nitrite in a pony-vials.
For phosphate and silicate in a pony-vial with 15 µl 5N HCl.

All samples were stored in a refrigerator at 4°C. Prior to analysis, all samples were brought to lab temperature in about one to two hours. The NH4 and NO3 plus NO2 samples were simultaneously measured in the other lab container within 12 hours of sub sampling.

Analytical methodology

The nutrient samples were analyzed on a QuAAtro auto-analyzer. Working standards were prepared freshly every day diluted from stock standards of the different nutrients into 0.2 µm filtered low nutrient seawater (LNSW). In the Black Sea (PE373), all measurements were calibrated with standards diluted in low nutrient seawater (LNSW) in the salinity range of the stations of the Black Sea at approximately 21 psu to ensure that analysis remained within the same ionic strength. The samples were measured from the lowest to the highest concentration in order to keep carry-over effects as small as possible, so from surface to deep waters. The nutrient stock solution is preserved using mercury chloride and has been used since 1997. Secondly a natural sterilized Reference Material for Nutrients (RMNS Kanso, Japan) containing a known concentration of silicate, phosphate, nitrate and nitrite in Pacific Ocean water, was analyzed in triplicate every run. The cocktail and the RMNS were both used to monitor the performance of the analysis. From every station the deepest sample is sub sampled for nutrients in duplicate, the duplicate sample vials were all stored dark at 4°C, and measured again with the next station, for statistical analysis.

The analysis chemistry is as follows:
Silicate reacts with ammonium molybdate to a yellow complex, after reduction with ascorbic acid, the obtained blue silica-molybdenum complex is measured at 820 nm. Oxalic acid is used to prevent formation of the blue phosphate-molybdenum (Strickland & Parsons, 1968).
Phosphate reacts with ammonium molybdate at pH 1.0, and potassium antimonyl-tartrate is used as an inhibitor. The yellow phosphate-molybdenum complex is reduced by ascorbic acid and measured at 880nm (Murphy & Riley, 1962).
Nitrate plus nitrite (NOx) is mixed with an imidazol buffer at pH 7.5 and reduced by a copperized cadmium column to nitrite. The reduction capacity of the cadmium coil was always better 95%. The nitrite is diazotated with sulphanylamide and naphtylethylene diamine to a pink colored complex and measured at 550nm. Nitrate is calculated by subtracting the nitrite value of the nitrite channel from the NOx value (Grasshoff et al, 1983).
Nitrite is diazotated with sulphanylamide and naphtylethylenediamine to a pink colored complex and measured at 550nm (Grasshoff et al, 1983).
Ammonium (NH4) reacts with phenol and sodiumhypochlorite at pH 10.5 to form an indophenolblue complex. Citrate is used as a buffer and complexant for calcium and magnesium at this pH. The blue color is measured at 630nm (Koroleff, 1969 and optimized by W. Helder and R. de Vries, 1979).
Hydrogen sulphide reacts para-aminodimethylaniline and ferric chloride to yield methylene blue which is measured at 660nm as described by Grasshof, K., 1969.

References Cited

Grasshoff K, Erhardt M, Kremling K., 1983. Methods of seawater analysis, 2nd revised and extended edition. Verlag Chemie, Weinheim

Grasshof, K., 1969. Advances in Automated Analysis, Technicon International Congress, 1969, Volume II, pp 147-150.

Koroleff, 1969 and optimized by W. Helder and R. de Vries, 1979 . An automatic phenolhypochlorite method for the determination of ammonia in sea- and brackish waters. Neth. J. Sea Research 13(1): 154-160.

Murphy, J. & Riley, J.P., 1962. A modified single solution method for the determination of phosphate in natural waters. Analytica chim. Acta, 27, p31-36

Stoll, M.H.C, Bakker K., Nobbe G.H., Haese R.R., 2011. Analytical Chemistry, Vol 73, Number 17, pp 4111-4116.

Strickland, J.D.H. and Parsons, T.R., 1968. A pracitcal handbook of seawater analysis. first edition, Fisheries Research Board of Canada, Bulletin. No 167, p.65.

BODC Data Processing Procedures

Data received from the originator were loaded into the BODC database using established BODC data banking procedures. The mapping between the originator's channels and BODC parameter codes is detailed in the table below, the originators quality control flags were changed to BODC quality control flags no other changes were made.

Data Quality Report

None