Metadata Report for BODC Series Reference Number 1620380

• 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.

36N Cruise CD171 Inorganic Nutrients Discrete Sampling Document

Cruise details

Content of data series

Data Acquisition and Analysis

A brief overview of how discrete samples were taken and analysed, adapted from the Cruise Report, is given below. Further information can be found in the Cruise Report (McDonagh et al, 2007).

A total of 144 CTD casts were completed on the cruise. The CTD configuration included a Sea-Bird 24 position Carousel with 24 20L Ocean Test Equipment (OTE) water samplers (Niskin bottles). A full-depth test station was occupied on 02/05/2005. A second test station, where all of the bottles were fired at 1000m, was occupied at 0700 on 03/05/05. The first station on the section (station 3) commenced at 1545. At station 50, the CTD cast went to 910 dbar where all bottles were fired. A CFC minimum occupied this depth and the samples were used by the transient tracer group to estimate the background concentration in the niskins or bottle blanks. Due to the early completion of station 98 there was time for an additional CFC bottle blank station (station 99) where all bottles were fired at 2600 m. No bottles were fired on Station 143 in order that the station could be completed in as timely a way as possible.

The 20L OTE water samplers were problematic throughout the cruise, in regards to not properly closing and sealing in the sample. Various configurations for preparing the samplers were attempted, as well as tightening the external springs. A total of 273 closing failures were logged, an average of 1.9 per cast.

Samples for inorganic nutrient analysis (NO₃ ^- + NO₂ ^-, PO₄ ^3- and Si(OH)₄) were taken from each CTD cast from station 3. Seawater was collected into 30 ml coulter counter vials after samples for CFCs, He, oxygen, CO₂, alkalinity, organic nutrients and salinity were drawn. Vials and lids were rinsed several times with seawater before sample collection. Samples were stored in a fridge and analysed within 1 to 8 hours.

Inorganic nutrients were measured by segmented continuous-flow using a Skalar San^plus autoanalyser. This system is set up for analysis and data logging with the Flow Access software package version 1.2.5. The analysis was calibrated with a set of 4 working standards containing nitrate, silicate and phosphate. The calibration range however, was modified for silicate analysis after station 114 in order to verify that concentrations higher than 40 µM were within a linear calibration range. 5 mM stock solutions were used to prepare working standards every 4 to 5 days. Stock standards were prepared with Milli-Q water, but working standards were prepared in a saline matrix (40 g NaCl/1 L Milli-Q water also referred to as artificial seawater), which was also used as the diluent for the analysis and analytical wash cups. The standards were stored in a fridge when not in use. Most CTD casts were analysed in single runs, which consisted of a set of standards, wash and drift cups, certified low nutrient sea water in order to test for contamination of the matrix and samples. The efficiency of the nitrate reduction column (i.e. cadmium column) was tested on a regular basis (2 to 5 days) by measuring and comparing prepared and certified nitrate and nitrite standards. Finally, the autoanalyser tubing was changed every 7-10 days.

On the 3rd day of the CD171 cruise the computer connected to the autoanalyser stopped retrieving baseline and peak signals from the integrator. This caused a delay with the nutrient analysis and samples from casts 3 to 7 were analysed after a day of collection. Although the actual reason for this malfunction was not found, the problem appeared to be related with the Skalar Flow Access software since after being re-installed communications between detectors, integrator and computer reestablished. On several occasions the nitrate and phosphate signals exhibited noisy baselines. In the case of nitrate, the main reason for this to happen was that fine cadmium granules from the reduction column entered the cell. This was easily resolved by removing the cell (while covering the light source) and allowing some bubbles in for 30-60 seconds. The cell was then placed back and the baseline checked before starting a run. In the case of the phosphate line the noise seemed to be due to chemicals sticking into cell. This problem was solved by washing the cell with 10% Deacon, Milli-Q water and artificial seawater (i.e. saline matrix) using a 60 ml syringe. It was also observed that when bad weather conditions persisted the signal of the three nutrients presented noisy baselines.

Problems with bottle closure during CD171 resulted in the use of bottle flag and sample flags following the convention of 2 = good, 3 = suspect, 4 = bad and 9 = absent.

BODC Discrete Data Processing Procedures

The data were supplied to BODC in a Matlab (.mat) file. This was converted to a comma separated value (CSV) format file. Methodology and units were checked against information held in the BODC parameter dictionary and an appropriate parameter codes were assigned. The file was then checked and loaded into the BODC database under the Oracle relational database management system without further modification.

The originator flagged the data as described previously. Flags described as "suspect" or "bad" by the originator were replaced with the appropriate BODC flag (see below). Data supplied by the originator as NaN (i.e. absent data) were not loaded to the database.

References

Fofonoff, N. P. and Millard Jr., R. C. (1983) Algorithms for computaions of fundamental properties of seawater. Unesco Technical Papers in Marine Science No. 44, 53 pp. Page 17.

McDonagh, E. L. et al (2007) RRS Charles Darwin Cruise 171, 01 May - 15 Jun 2005: A transatlantic hydrography section at 36°N. Southampton, UK, National Oceanography Centre Southampton, 127pp. (National Oceanography Centre Southampton Cruise Report, 14) Available online

BODC Quality Control Flags

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

Project Information

36 North Project

Project Overview

The 36 North project aims to investigate and understand the influences on global climate regulation, with a focus on the current role of the North Atlantic subtropical gyre.

It will seek to further understand the mechanisms which control the heat transport, nutrient and carbon budgets of the North Atlantic Ocean. This will impact on our understanding of how the ocean is warming, phytoplankton growth and how oceans uptake CO2.

This project brings together scientists from the National Oceanography Centre, Southampton (NOCS), the University of Liverpool, the Plymouth Marine Laboratory (PML) and the University of East Anglia (UEA). It will run from 1 October 2004 to 30 September 2008 and is funded by a Natural Environment Research Council consortium grant.

Aims

The main aims include:

• To examine how nitrogen, phosphorous and carbon bugets are closed.
• To examine how nutrient and carbon budgets are controlled.
• To assess the heat flux across the 36 N section (and poleward using World Climate Circulation Experiment (WOCE) data).

Methods

This will be achieved by:

• A detailed, hydrographic survey along 36N with a complete biogeochemical analysis of data collected during RRS Charles Darwin cruise 1 May - 15 June 2005 (CD171).
• The development and application of inverse and coupled biogeochemical, isopycnic circulation models.
• Comparison with historical data collected by RRS Discovery during 4 April - 10 May 2004 (D279).
• Comparison with three additional North Atlantic cruises undertaken in 2004/2005, funded under the Rapid Climate Change (RAPID) and Atlantic Meridional Transect (AMT) programmes.

Data Activity or Cruise Information

Data Activity

BODC Sample Metadata Report for CD171_CTD_CTD171115

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: