Metadata Report for BODC Series Reference Number 1869156

• 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

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.

AMT12 dissolved methane and nitrous oxide concentration and saturation measurements from CTD bottle samples

Originator's Protocol for Data Acquisition and Analysis

Water samples were collected using a Sea-Bird 911plus CTD system fitted with 24 x 20 litre "Ocean Test Equipment" (Niskin type) external spring water bottles. Casts were completed predawn to minimise diurnal effects. Subsamples from the CTD bottles were collected in 1 litre volumetric flasks (Fisher), allowing overflow of the sample, to preclude contamination by air bubbles. Each sample was poisoned using 200ml of 0.25M aqueous HgCl₂ and sealed with a ground glass stopper. The sample flasks were stored at room temperature for 0-8 hours, which treatment should result in no significant change in N₂O (Elkins, 1980).

N₂O and CH₄ partial pressures and concentrations were measured by single phase equilibration gas chromatography, using the analytical apparatus described by Upstill-Goddard et al. (1996). The system was flushed with equilibrator gas (compressed air) and sealed. The sample to be analysed was warmed, in its sealed flask, to a constant 25°C. The glass stopper was then replaced with the equilibrator manifold, and the joint sealed with PTFE tape and a joint clip.

A headspace was created in the sample flask by introduction of compressed air with ambient N₂O and CH₄ mixing ratios of 318 ppbv and 1.79 ppmv respectively. The headspace was circulated through a closed circuit to return to the sample flask through a solvent filter (Jones Chromatography) with a period of 12 minutes. Two sample loops (one each for N₂O and CH₄) were simultaneously flushed with ultra high purity nitrogen carrier gas. Each sample run was followed by a standard (made from secondary standards), and then by ambient air analysis. Shimadzu Class VP software was used for the analysis of N₂O and CH₄ hromatograms. Run time of the system was typically 35 minutes. The water phase of the sample was measured gravimetrically.

N₂O analysis

CO₂ and water vapour were removed from the gas stream using stainless steel tubing (internal diameter 3.8 cm) packed with 1.22 cm³ Carbosorb and 1.2 cm³magnesium perchlorate (Mg(ClO₄)), respectively. The N₂O in the headspace was detected with an Electron Capture Detector (ECD), utilizing a 15 m Ci⁶³Ni source, and operated at 320°C and 1.0 nA. The flow rate of 24 ml min^-1 resulted in a retention time of 7.43 minutes.

CH₄ analysis

Water vapour was removed from the gas stream using stainless steel tubing (internal diameter 3.8 cm) packed with 1.2 cm³ magnesium perchlorate (Mg(ClO₄)). The CH₄ in the headspace was determined by Flame Ionisation Detection using CP grade hydrogen (BOC) and compressed air (BOC) to support combustion at 120°C. The flow rate of 20 ml min^-1 resulted in a retention time of 0.97 minutes.

References Cited

Elkins J.W., 1980. Determination of dissolved nitrous oxide in aquatic systems by gas chromatography using electron-capture detection and multiple phase equilibration. Analytical Chemistry, 52, 262-267.

Upstill-Goddard R.C., Rees A.P. and Owens N.J.P., 1996. Simultaneous high-precision measurements of methane and nitrous oxide in water and seawater by single-phase equilibration gas chromatography. Deep-Sea Research Part I, 43(10), 1669-1682.

BODC Data Processing Procedures

Data were submitted via email in an Excel spreadsheet archived under BODC's accession number UEA050040. Sample metadata (Latitude, longitude, ctd cast, station number and depth) were checked against information held in the database. There were no discrepancies.

The concentration data were provided in nanomoles per litre and percent. These units for the concentration data were consistent with the BODC parameter code units and no conversions were applied.

The data were reformatted and loaded in BODC's samples database under Oracle Relational Database Management System. Data were marked up with BODC parameter codes and loaded into the database. Individual samples were matched through CTD cast and depth.

A parameter mapping table is provided below:

Data Quality Report

BODC was not advised by the data originator of any quality issues with the data.

Project Information

The Atlantic Meridional Transect - Phase 2 (2002-2006)

Who was involved in the project?

The Atlantic Meridional Transect Phase 2 was designed by and implemented by a number of UK research centres and universities. The programme was hosted by Plymouth Marine Laboratory in collaboration with the National Oceanography Centre, Southampton. The universities involved were:

• University of Liverpool
• University of Newcastle
• University of Plymouth
• University of Southampton
• University of East Anglia

What was the project about?

AMT began in 1995, with scientific aims to assess mesoscale to basin scale phytoplankton processes, the functional interpretation of bio-optical signatures and the seasonal, regional and latitudinal variations in mesozooplankton dynamics. In 2002, when the programme restarted, the scientific aims were broadened to address a suite of cross-disciplinary questions concerning ocean plankton ecology and biogeochemistry and the links to atmospheric processes.

The objectives included the determination of:

• how the structure, functional properties and trophic status of the major planktonic ecosystems vary in space and time
• how physical processes control the rates of nutrient supply to the planktonic ecosystem
• how atmosphere-ocean exchange and photo-degradation influence the formation and fate of organic matter

The data were collected with the aim of being distributed for use in the development of models to describe the interactions between the global climate system and ocean biogeochemistry.

When was the project active?

The second phase of funding allowed the project to continue for the period 2002 to 2006 and consisted of six research cruises. The first phase of the AMT programme ran from 1995 to 2000.

Brief summary of the project fieldwork/data

The fieldwork on the first three cruises was carried out along transects from the UK to the Falkland Islands in September and from the Falkland Islands to the UK in April. The last three cruises followed a cruise track between the UK and South Africa, only deviating from the traditional transect in the southern hemisphere. During this phase the research cruises sampled further into the centre of the North and South Atlantic Ocean and also along the north-west coast of Africa where upwelled nutrient rich water is known to provide a significant source of climatically important gases.

Who funded the project?

Natural Environment Research Council (NERC)

Data Activity or Cruise Information

Data Activity

BODC Sample Metadata Report for AMT12_CTD_AMT12_07

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.

Related Data Activity activities are detailed in Appendix 1

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:

Appendix 1: AMT12_CTD_AMT12_07

Related series for this Data Activity are presented in the table below. Further information can be found by following the appropriate links.

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