Metadata Report for BODC Series Reference Number 1268576

• 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.

Inorganic nutrient measurements from CTD bottle samples collected during cruise JR20100319 (JR235, JR236, JR239)

Originator's Protocol for Data Acquisition and Analysis

Water samples for the determination of nitrate and nitrite, phosphate and silicate were drawn from 20 litre Niskin bottles from a 24-rosette sampling system mounted on a Sea-Bird 9/11 plus CTD (s/n 09P-0869). Casts 1-68 were part of the ANDREX project and casts 70-98 were part of the BAS Polar Oceans strategic research programme. Some bottles were leaking badly and were excluded from any sampling. Over the course of the cruise, the bottles had a success rate of 89% (judged by successful closure and non-leakage). This rate was markedly lower towards the start of the cruise before work was undertaken during the cruise to help improve the success rate. Please see the cruise report which provides further information about the bottle problems and summarises the modifications made to the Niskin bottles.

Water samples from the Niskin bottles were collected directly into 30 mL plastic pots. Pots were rinsed with sample water at least three times before drawing the sample. Samples were stored in a fridge at approximately 4 °C until sampling for two or three stations were completed. Analyses were thus carried out for typically 2-3 stations at a time. This was done in order to avoid excess production of waste, given that waste was to be returned to the UK.

Most analyses were started within 2-12 hours of sample collection using a segmented continuous-flow Skalar SansPlus autoanalyser set up for analysis and data logging with the Flow Access Software version 1.3.11 following Kirkwood (1996), with the exception that the pump rates through the phosphate line were increased by a factor of 1.5, which improves reproducibility and peak shape. A dilution loop for the silicate channel was also installed giving a 2.9 times dilution. This was done in anticipation of the high silicate concentrations typical of the Southern Ocean. All labware was washed with 10% HCl and rinsed with MQ water previous to the cruise and several times before use once onboard. The autoanalyser was washed through with 10% Decon 90 then Milli-Q water for at least 15-30 minutes each after each run when the time between stations allowed, otherwise the autoanalyser was left with the reagent tubing connected ready for the next run. New pump tubing and lamps were fitted at the start of the cruise, along with a new cadmium column. All tubing was turned around on the 8th of April 2010 and the cadmium column was replaced (from run 25). The analysis was calibrated using a set of five standards. Approximately 5 mMol L^-1 of stock standard solutions prepared in Milli-Q water were used to produce working standards. Working standards were prepared in a saline solution (40 g NaCl in 1 L of Milli-Q water, artificial seawater), which was also used as a diluent for the analysis. New batches of artificial seawater were prepared almost once every 2 weeks. These were analysed prior to being used in order to check for contamination and consistency. Certified Ocean Scientific International (OSIL) Low Nutrient Seawater (LNSW) was measured in duplicate in every run in order to test artificial seawater for contamination.

LNSW was also used as a quality control in order to check for the reproducibility of low nutrient concentrations. The performance of the autoanalyser was monitored by producing time series plots of the following parameters: standards concentration, baseline, calibration slope (instrument sensitivity), calibration correlation coefficient, nitrate reduction efficiency, low nutrient seawater and certified standards. The precision of the method was determined by monitoring the variations of the complete set of standards measured throughout the cruise. Triplicate analyses were performed on the first and last sample of every station, plus in a randomly selected sample for most station. These showed the sample variability of replicates from a given mean concentration was in general <0.5%, <0.3% and <0.5% for nitrate, silicate and phosphate respectively. The limits of detection of this method were estimated as twice the standard deviation of the concentration of lowest standard of each nutrient. The limits of detection of this method during were 0.01 mmol L^-1 for Phosphate, 0.13 mmol L^-1 for nitrate+nitrite and 0.15 mmol L^-1 for silicate. Further information about the standards used can be found in the cruise report.

Data processing was undertaken using Skalar proprietary software and was done at regular intervals throughout the cruise. Time series of baseline, instrument sensitivity, calibration curve correlation coefficient, nitrate reduction efficiency and duplicate difference was compiled to check the performance of the autoanalyser over the course of the cruise.

References Cited

Kirkwood, D., 1996. Nutrients: Practical notes on their determinations in seawater. ICES Techniques in marine environmental sciences. 17, 1-25.

BODC Data Processing Procedures

All data were received in csv formatted file and were loaded into the BODC database using established BODC data banking procedures. The data were screened in-house prior to loading. Data were then loaded without any further changes. The following table shows how the variables were mapped to appropriate BODC parameter codes:

Data Quality Report

All WOCE quality control flags provided by the originator were converted into BODC standard flags, 2 (good) = no flag, 3 (questionable) and 4 (bad) = 'L', and all absent data values were removed. No further flags were added by BODC.

Problem Report

None (BODC assessment).

Project Information

Antarctic Deep Water Rates of Export (ANDREX) project document

ANDREX is a UK field programme aimed at investigating the role of the Weddell Gyre in the Meridional Overturning Circulation (MOC) and its influence on deep ocean properties.

The MOC is a critical regulator of Earth's climate and is crucial for deep water ventilation across the globe. Surface currents transport waters towards the poles, where they become dense and sink, flowing equatorward as deep, cool currents. The MOC ensures that the deep oceans remain ventilated and conducive to life, and is also important for anthropogenic carbon sequestration. The southern closure of the MOC in the Weddell Sea is strongly influenced by the Weddell Gyre, which facilitates the exchange of waters between the Antarctic Circumpolar Current (ACC) and the waters of the continental shelf. Cooling and sea ice formation in the Weddell Sea lead to overturning of the water column and the ventilation of Antarctic Bottom Water (AABW), which flows out of the Weddell Sea and into the deep oceans to the north. Thus, the Weddell Gyre plays an important role in the properties of deep ocean waters on a global scale.

The goals of ANDREX are to investigate the exchange of water masses between the ACC and the Weddell Sea, including AABW formation and ventilation rates, carbon and nutrient cycling, the influence of fresh water input from sea ice, precipitation and glacial melt, and the role of the Weddell Gyre in anthropogenic carbon sequestration. The project includes hydrographic, ventilation tracer, biogeochemical and bathymetric measurements along the outer rim of the Weddell Gyre.

ANDREX is funded by the UK Natural Environment Research Council (NERC) Antarctic Funding Initiative (AFI) and involves scientists from the National Oceanography Centre, Southampton (NOC), the British Antarctic Survey (BAS), the University of East Anglia (UEA), the University of Manchester, the Alfred Wegener Institut (AWI) and the Woods Hole Oceanographic Institution (WHOI).

For more information please see the official project website at ANDREX

Data Activity or Cruise Information

Data Activity

BODC Sample Metadata Report for JR20100319_CTD_CTD22

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: