Metadata Report for BODC Series Reference Number 1748359

• 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

Dissolved nutrient data series for Marine Productivity cruises RRS Discovery DI258, DI262, DI264 and DI267

Data Originator

Richard Sanders, Southampton Oceanographic Centre (SOC)

Content of data series

Sampling strategy and methodology

Samples for nutrient analyses were collected from water bottle rosette sampling systems mounted on CTD and ARIES net system and from ship's non-toxic seawater supply.

Concentrations of nitrate + nitrite, reactive orthophosphate and orthosilicic acid were measured on unfiltered water samples using a Skalar Sanplus autoanalyser. Samples collected using the CTD system were drawn directly from the Niskin bottles into brand new 40ml Coulter Counter vials. Samples collected using the ARIES towed system were drawn through a tube into brand new 40ml Coulter Counter vials. Both sets of samples were stored at 4°C in darkness prior to analysis and analysed as soon as practicable. Analysis generally took place within 12 hr but was delayed by as much as 24-36 hours towards the end of the cruise due to computer failure.

The analytical methods employed followed those laid out by Kirkwood in the user manual supplied by Skalar with the exception of modifications to the phosphate samples and phosphate reagents flow rates (see cruise report for details). Prior to 20 November two samples per station were analysed in duplicate. From 20 November, all samples were analysed in duplicate.

Version 1.4 of the Scalar-supplied processing software was used with both the baseline and drift corrections applied. Following the completion of a run the peak assignment was manually checked and any electrical spikes/ bubbles, poorly formed peaks or mis-assigned peaks corrected. Excel files were then created of the results and these combined with the dissolved oxygen results to create a single results file for each station. Prior to 15 November the single analysis of each sample was reported; after 20 November the mean of the two determinations was reported unless there were reasons for rejecting one of them. This was particularly the case for some of the phosphate peaks (see later discussion). Finally a further QC check was undertaken by eliminating datapoints on a case by case basis that deviated from the bulk Redfield ratio calculated for the cruise split into four sections (pre and post-storm on leg 1, and pre and post-medevac on leg 2). Each line was cleaned daily using a solution of 10% decon and exceptionally 10% NaOH (phosphate) by pumping it through the lines for 15 min at the beginning and end of each day. Where time allowed, a regime of cleaning after each run was introduced.

10 mM Standards were prepared fresh from weighed dried salts on 2 and 3 November. Working standards (40, 30, 20, 10 uM Si, 20, 15, 10, 5 N, 2, 1.5, 1, 0.5 µM P) were prepared on a daily basis by dilution into nutrient-free artificial seawater. It was noted that on occasions residual phosphate peaks were present in the diluting seawater (c 0.05 µM). This factor has not been corrected for. Secondary standards prepared on 4 November and 14 December were intercalibrated against Ocean Scientific International marine nutrients kit standards on the same days. The intercomparison conducted early in the cruise immediately after the replacement of the power supply was unsatisfactory as the concentrated solutions supplied by OSI contain nutrients in addition to the one they are the standard for. No further intercomparison was possible at this point as station work began almost immediately. The comparison undertaken on 14 December yielded the following values for the SOC standards (value in parentheses represents the nominal concentration):

• P: 1.46, 1.48, 1.49, 1.52, 1.5 M (1.5 M)
• N: 14.91, 14.95, 14.97, 14.93, 14.94 M (15 M)
• Si: 15.68, 15.67, 15.68, 15.79, 15.6 M (15 M)

It was planned to use the same primary standards for the entire series of MarProd cruises, and they were returned to SOC at the end of this cruise for further testing (particularly the silicate standard). A bulk sample was taken on the first station in the western Iceland basin (14191) station in the deep Antarctic bottom water layer. This sample was run in duplicate on each analytical run. A 20 M nitrite solution was run on each run to evaluate the reduction efficiency of the cadmium column. On a day to day basis the following instrument parameters were logged: slope of the calibration curve (bits/ M); baseline; the correlation coefficient (R2 value) of the calibration curve; and a parameter described in the Skalar software manual as the relative standard deviation of the calibration curve. In practice this turns out to be closely related to the correlation coefficient of the calibration curve and it has therefore not been reported here.

The phosphate line gave problems throughout leg 2. This was manifested by sudden, dramatic increases in baseline and deterioration in peak quality, particularly in the second or third run of the day. Overall somewhere around one half of the runs were affected to some extent. On all but one occasion a set of sample analyses was completed with a large number of duplicates. This was the final run of ARIES cast 14296. For this station no P data have been reported. Further to this problem, odd individual phosphate peaks that appeared to be erroneous were manually edited from results files.

A full report on the performance of the analyser, nitrite column efficiency and analytical precision is available from the cruise report.

BODC Processing

The nutrient data were extracted from the PSTAR SAMnnnnn files generated on board and transferred into an ASCII format. Methodology and units were checked against information held in the BODC parameter dictionary and an appropriate parameter code was attributed to each variable. The file's data and metadata fields were then checked prior to loading into a database.

A number of samples corresponded to analyses carried out on samples collected from duplicate Niskin bottles (defined when the depth firing range between two bottles overlaps). Since this is incompatible with BODC's database structure, the nutrient concentration was averaged prior to loading. 9 duplicate values were averaged for each nutrient type. Difference between duplicate values prior to averaging was generally small and never exceeded 0.2µM for nitrite+nitrate, 0.05µM for phosphate and 0.1µM for silicate.

The data were loaded into the database under the Oracle Relational Database Management System by matching the sample's station identifier and depth with the information already held in the database for this cruise. The data were successfully loaded without further modification.

Skalar San+ Autoanalyzer

The San+ Autoanalyzer is an Automated Wet Chemistry Analyzer (Continuous Flow Analyzer) which has been designed as a modular system to measure a variety of water chemistry characteristics, such as nutrient concentrations in seawater. Individual modules are tailored to specific needs. It uses Continuous Flow Analysis (CFA), allowing up to 16 analytical measurements to be made on a single sample simultaneously. The system comprises a sampler, chemistry section, detector and specialist software.

Chemistry section
The San+ includes a chemistry section which has hundreds of applications. It houses up to five chemistry cartridges with built-in dosing pump and air injection systems, up to five interchangeable cartridges with build-in photometric detectors and five separate waste receptacles. The throughput of the analyser depends upon application and can vary from 25 to 120 analyses per hour. It has a double diameter pump deck for accurate dosing with 32 pump tubes, two separated pump decks for 2 x 2 channel concept, and controlled synchronised eight channel air injection with separate built-in compressor for increased flow stability and fast start-up. It has easy access to chemistry cartridges with flexible ultra low carry-over connections between dialysers, reactors, coils, flow cells and other components, leak detection, 3-cuffs long life pump tubes, and has manually operated and automatic rinsing valves for easy automatic start up and overnight operation.

Detectors
The San+ range of detectors comprises dual channel colorimetric detectors, the unique matrix correction detector with automatic background correction for difficult sample matrixes, but also covers a range of detectors for I.R., U.V., fluorimetry, ISE, flame photometry, refractometers, density meters, etc.

Software
The San+ 'Flow Access' windows software package controls the complete analyser, with auto start-up, function control, and auto-scaling, pre-and post run sample dilutions, result calculation and statistics. Up to 16 channels can be handled simultaneously, with multiple samplers, and chemistries can be grouped for analysis.

The San+ is also known as San++.

Niskin Bottle

The Niskin bottle is a device used by oceanographers to collect subsurface seawater samples. It is a plastic bottle with caps and rubber seals at each end and is deployed with the caps held open, allowing free-flushing of the bottle as it moves through the water column.

Standard Niskin

The standard version of the bottle includes a plastic-coated metal spring or elastic cord running through the interior of the bottle that joins the two caps, and the caps are held open against the spring by plastic lanyards. When the bottle reaches the desired depth the lanyards are released by a pressure-actuated switch, command signal or messenger weight and the caps are forced shut and sealed, trapping the seawater sample.

Lever Action Niskin

The Lever Action Niskin Bottle differs from the standard version, in that the caps are held open during deployment by externally mounted stainless steel springs rather than an internal spring or cord. Lever Action Niskins are recommended for applications where a completely clear sample chamber is critical or for use in deep cold water.

Clean Sampling

A modified version of the standard Niskin bottle has been developed for clean sampling. This is teflon-coated and uses a latex cord to close the caps rather than a metal spring. The clean version of the Levered Action Niskin bottle is also teflon-coated and uses epoxy covered springs in place of the stainless steel springs. These bottles are specifically designed to minimise metal contamination when sampling trace metals.

Deployment

Bottles may be deployed singly clamped to a wire or in groups of up to 48 on a rosette. Standard bottles and Lever Action bottles have a capacity between 1.7 and 30 L. Reversing thermometers may be attached to a spring-loaded disk that rotates through 180° on bottle closure.

Project Information

No Project Information held for the Series

Data Activity or Cruise Information

Data Activity

No Document Information Held for the Series

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: