Metadata Report for BODC Series Reference Number 1250499

• Metadata Summary

• Problem Reports

• Data Access Policy

• Narrative Documents

• Project Information

• Data Activity or Cruise Information

• Fixed Station Information

• BODC Quality Flags

• SeaDataNet Quality Flags

Metadata Summary

Problem Reports

No Problem Report Found in the Database

Data Access Policy

Open Data supplied by Natural Environment Research Council (NERC)

You must always use the following attribution statement to acknowledge the source of the information: "Contains data supplied by Natural Environment Research Council."

Narrative Documents

GO-FLO Bottle

A water sampling bottle featuring close-open-close operation. The bottle opens automatically at approximately 10 metres and flushes until closed. Sampling with these bottles avoids contamination at the surface, internal spring contamination, loss of sample on deck and exchange of water from different depths.

There are several sizes available, from 1.7 to 100 litres and are made of PVC with a depth rating of up to 500 m. These bottles can be attached to a rosette or placed on a cable at selected positions.

Nutrients as part of BOFS project

Document History

Converted from CDROM documentation.

Sampling strategy and methodology

This document describes the methodology used to derive the nutrient data which constitutes a subset of the bottle data (discrete samples) assembled from the BOFS Atlantic cruises.

Five nutrient species (nitrate, nitrite, silicate, phosphate, ammonium) were determined from discrete bottle samples and the methodology of the five analyses is described here.

Each nutrient has been documented for sampling and analytical methodologies from information supplied by the analysts; operational information was also supplied by Research Vessel Services (RVS).

Acquisition, Processing and Editing

Water bottle samples were obtained either from the General Oceanics Rosette Multisampler (fitted with twelve 10-litre Go-Flo or Niskin water bottles), which was attached to a Neil Brown Mk 3B CTD, or from 7-litre Niskin water bottles, lowered from the electric hydrographic winch.

Individual datasets of water bottle data were largely worked up post-cruise by the responsible scientist and submitted to BODC for loading to the database. Datasets were uniquely identified and cross-referenced, using time and depth as the primary linking keys.

Quality control was primarily the responsibility of the data originator. However, any errors detected by database users or BODC have been corrected.

Nutrients by AutoAnalysis

There were two AutoAnalysers used for nutrient analysis on BOFS cruises; a Technicon AutoAnalyser supplied by PML and a ChemLab AutoAnalyser supplied by RVS, which were deployed as follows:

Discovery cruises 182,183,184,190,191,192 = Technicon
Charles Darwin cruises 53,60,61 = Technicon
Charles Darwin cruises 46,47 = ChemLab

The basic chemistry of the two analytical systems is identical; the only real difference between the two instruments is the flow rate through them and the optical precision of the colorimeters which is superior in the Technicon system. As far as possible, analysis of discrete samples was undertaken in near-continuous mode to avoid introducing air bubbles to the AutoAnalyser and to minimise air-borne contamination.

Nitrite

Nitrite was determined by diazotization and coupling to form a dye. The nitrite ions react with an acidic sulphanilamide solution to form a diazo compound; this is then reacted with N-1- naphthylethylenediamine dihydrochloride (NEDD) to form a reddish purple azo dye.

Analysis was colorimetric at 540nm (after Armstrong et al (1967)). Standardisations were done with solutions made up from pre-weighed standards (6.90 grams sodium nitrite in 1 litre with 1ml chloroform as preservative = 100mM; after Grasshoff (1976)) and either 'nutrient-depleted' surface seawater or Milli-Q water as follows:

Discovery cruises 182,183,184,190,191,192 = Milli-Q
Charles Darwin cruises 46,47,53,60,61 = nutrient-depleted surface seawater

Nitrate

The analysis is for the sum of nitrate and nitrite ions; the chemistry is the same as for nitrite analysis but is preceded by the reduction of nitrate to nitrite using a copper/cadmium column in an ammonium chloride solution (pH 8.5). No attempt was made to subtract the nitrite contribution to the total concentration; results are expressed in terms of total nitrate and nitrite ions.

Standardisations were done with solutions made up from pre-weighed standards (10.11 grams potassium nitrate in 1 litre with 1ml chloroform as preservative = 100mM; after Grasshoff (1976)) and either 'nutrient-depleted' surface seawater or Milli-Q water as follows:

Discovery cruises 182,183,184,190,191,192 = Milli-Q
Charles Darwin cruises 46,47,53,60,61 = nutrient-depleted surface seawater

Ammonia

The analysis is based on the production of an indophenol blue complex (colorimetric analysis at 630nm) and is very dependent on reaction pH, optimally 10.6. (Optimum temperature 55°C). For fuller details of the technique, see Mantoura and Woodward (1983).

Standardisations were done with solutions made up from pre-weighed standards (0.66 grams ammonium sulphate in 1 litre with 1ml chloroform as preservative = 10mM) and either 'nutrient- depleted' surface seawater or Milli-Q water as follows:

Discovery cruises 182,183,184,190,191,192 = Milli-Q
Charles Darwin cruises 46,47,53,60,61 = nutrient-depleted surface seawater

On Discovery cruise 191, there was a slight modification to the analysis in that the amount of trisodium citrate (normally 30g per 100mls) was increased to lower the pH of the reaction and thus prevent the formation of precipitate in the reagent lines. This was a minor adjustment and did not significantly alter the chemistry of the reaction or analysis.

Silicate

Analysis involves the reaction of inorganic silicate with ammonium molybdate to form silicomolybdic acid. This is then reduced by ascorbic acid to form a silico-molybdenum blue complex (analysis at 630nm). Addition of oxalic acid ensures no competitive reaction from phosphates. More details of the technique can be found in Kirkwood (1989).

Standardisations were done with solutions made up from pre-weighed standards (21.214 grams sodium metasilicate penta hydrate in 1 litre with 1ml chloroform as preservative = 100mM; this standard should NOT be stored in glass) and either 'nutrient-depleted' surface seawater or Milli-Q water as follows:

Discovery cruises 182,183,184,190,191,192 = Milli-Q
Charles Darwin cruises 46,47,53,60,61 = nutrient-depleted surface seawater

Phosphate

This method is based on the production of a blue phospho-molybdenum complex by reaction with molybdate and ascorbic acid. The pH needs to be kept less than 1 to avoid a competitive reaction from silicate. Analysis was at 880nm.

Standardisations were done with solutions made up from pre-weighed standards (13.609 grams potassium dihydrogen orthophosphate in 1 litre with 1ml chloroform as preservative = 100mM) and either 'nutrient-depleted' surface seawater or Milli-Q water as follows:

Discovery cruises 182,183,184,190,191,192 = Milli-Q
Charles Darwin cruises 46,47,53,60,61 = nutrient-depleted surface seawater

Nutrient intercalibrations

The following intercalibrations were carried out for nutrient data:

The intercalibrations relate to the methodology, the instruments used and the analyst. Intercalibrations generally involved the exchange of standards, each standard being analysed on all participating ships and the simultaneous deployment of CTDs, each depth being analysed on all participating ships (this did not involve any exchange of bottle samples between ships). Due to operational constraints, 'adjacent' CTDs from different ships may be more than 2 nautical miles apart.

No data from Meteor are included: these were requested via the JGOFS Office from IFM-Kiel, but could not be obtained.

Discovery-Atlantis-Meteor intercalibration

The results from the intercalibration deep CTD cast are as follows:

This shows an approximate 16% overestimate of nitrate by Discovery relative to Atlantis and a 150% overestimate of phosphate by Discovery relative to Atlantis. However, from the depth profiles, it is apparent that Discovery is either sampling a different midwater water mass than Atlantis or the actual depth of bottle firings have been misaligned and there is only evidence for a systematic offset in the determinations of phosphate. During the intercalibration CTD cast, Discovery and Atlantis were approximately 2.5 nautical miles apart.

Charles Darwin 46 - Tyro intercalibration

Exchange of nutrient standards revealed a 10% overestimate of Tyro's nitrate standard, a 6% overestimate of phosphate and a slight underestimate of silicate by Darwin as follows:

Tyro standards:

Intercalibration cast:

Although there is some indication that different water masses were sampled in the 400-1000m depth range, the depth profiles are broadly similar and reveal a 5% overestimate of nitrate by Darwin relative to Tyro, a 12% underestimate of silicate and a 45% overestimate of phosphate.

Charles Darwin 47 - Discovery 191 intercalibration

Results of the intercalibration CTD cast are as follows:

The depth profiles indicate differences in the surface waters sampled, with Discovery apparently better able to sample the nutrient-poor surface waters. Overall, Darwin underestimated nitrate by 6%, overestimated nitrite by 56%, underestimated silicate by 18% and overestimated phosphate by 47% relative to Discovery.

Darwin 47 - Discovery 192 intercalibration

The results of the intercalibration CTD cast are as follows:

In this instance, Darwin was better able to sample surface nutrient-poor waters as no Discovery samples were available for the top 30m. Generally, Darwin overestimated all 4 nutrient species relative to Discovery; nitrate by 20%, nitrite by 79%, silicate by 10% and phosphate by 22%.

Comments on data quality

The intercalibrations show significant differences between the participating vessels. However, in these cases it is difficult to categorically state which determination is absolutely correct. It is also dangerous to assume that comparisons determined from a single analysis apply to an entire cruise.

With respect to the BOFS data, it is acknowledged that problems with the autoanalyser were encountered on some cruises. However, the data have been examined carefully and many rejected prior to inclusion in the database or subsequently flagged as questionable.

There was much discussion in the BOFS community concerning the quality of the nutrient data. Critical examination of the data by BODC has shown them to be largely internally consistent. However, because an element of doubt has been expressed, users are advised to look at the data set as a whole and draw their own conclusions about their accuracy.

Feedback about individual data values or profiles deemed suspect, but not flagged as such in the data file would be much appreciated and should be directed to BODC. Please quote the BODC bottle references with any such comments.

References

Armstrong, F.A.J., Stearns, C.R. and Strickland, J.D.H (1967). The measurements of upwelling and subsequent biological processes by means of the technicon AutoAnalyzer and associated equipment. Deep Sea Research 14: 381-389.

Brewer and Riley (1965). The automatic determination of nitrate in sea water. Deep Sea Research 12: 765-772.

Grasshoff, K. (1976). Methods of seawater analysis. Verlag Chemie, Weiheim: pp317.

Kirkwood, D.S. (1989). Simultaneous determination of selected nutrients in sea water. ICES CM/C:29.

Mantoura, R.F.C. and Woodward, E.M.S. (1983). Optimization of the indophenol blue method for the automated determination of ammonia in estuarine waters. Estuarine Coastal and Shelf Science 17: 219- 224.

Price, N.M. and Harrison, P.J. (1987). Comparison of methods for the analysis of dissolved urea in seawater. Marine Biology 94: 307-317.

Woodward, E.M.S. (1992). Nutrient analysis techniques. PML internal report.

Project Information

Biogeochemical Ocean Flux Study (BOFS)

The Biogeochemical Ocean Flux Study (BOFS) was a Community Research Project within the Marine and Atmospheric Sciences Directorate (MASD) of the Natural Environment Research Council. The project provided a major United Kingdom contribution to the international Joint Global Ocean Flux Study (JGOFS). The project ran from April 1987 until March 1992 but was extended through bridging funds until March 1993. The BOFS North Atlantic Data Set was collected during the initial five year period. Fieldwork in the bridging year focused on the Antarctic in late 1992. These data will form part of a subsequent electronic publication of Antarctic data and are not included on this CD-ROM.

The primary aims of the BOFS programme were:

• To improve the understanding of the biogeochemical processes influencing the dynamics of the cycling of the elements in the ocean and related atmospheric exchanges with particular reference to carbon.
  
  
• To develop, in collaboration with, other national and international programmes. models capable of rationalising and eventually predicting the chemical and biological consequences of natural and man-induced changes to the atmosphere ocean system.

A Community Research Project brings together scientists from NERC institutes and UK universities to work on a common problem. In this way resources far beyond the scope of individual research groups may be brought to bear on a common problem. The project is coordinated through a host laboratory which has responsibility for financial management, organisation and logistics. The host laboratory for BOFS was the Plymouth Marine Laboratory (PML).

Fieldwork

The BOFS North Atlantic data set was the result of fieldwork carried out on 11 research cruises. Four studies were carried out during three field seasons in 1989, 1990 and 1991; the 1989 North Atlantic Bloom Experiment, the 1990 Lagrangian Experiment, the 1990 BOFS Benthic Study and the 1991 Coccolithphore Study. Measurements taken include:

Physical (e.g. temperature, salinity and optics)
Meteorology and positioning
Chemical (e.g. dissolved oxygen, organic carbon and nitrogen)
Biological (e.g. biomass, pigments and bacteria production)
Geological (sediment traps)

The Sterna 1992 project (the Southern Ocean component of BOFS) aimed to measure the size and variability of carbon and nitrogen fluxes during early summer in the Southern Ocean, with particular emphasis on rates and processes in the marginal ice zone. Fieldwork was carried out between October and December 1992 in the Southern Ocean area, approximately 55°S to 70°S, 60°W to 85°W. A wide range of physical, chemical and biological parameters were measured.

Data Management

Data management services to BOFS were provided by the British Oceanographic Data Centre, funded by the UK Natural Environment Research Council.

Data Activity or Cruise Information

Data Activity

BODC Sample Metadata Report for DI184_CTD_11892#1

Please note:the supplied parameters may not have been sampled from all the bottle firings described in the table above. Cross-match the Sample Reference Number above against the SAMPRFNM value in the data file to identify the relevant metadata.

Cruise

Complete Cruise Metadata Report is available here

Fixed Station Information

No Fixed Station Information held for the Series

BODC Quality Control Flags

The following single character qualifying flags may be associated with one or more individual parameters with a data cycle:

SeaDataNet Quality Control Flags

The following single character qualifying flags may be associated with one or more individual parameters with a data cycle: