Metadata Report for BODC Series Reference Number 1342777


Metadata Summary

Data Description

Data Category Water sample data
Instrument Type
NameCategories
Niskin bottle  discrete water samplers
Instrument Mounting lowered unmanned submersible
Originating Country United Kingdom
Originator Mr Francois-Eric Legiret
Originating Organization National Oceanography Centre, Southampton
Processing Status banked
Project(s) Rapid Climate Change Programme
 

Data Identifiers

Originator's Identifier D346_CTD_NUTS_3216:C052
BODC Series Reference 1342777
 

Time Co-ordinates(UT)

Start Time (yyyy-mm-dd hh:mm) 2010-01-19 01:59
End Time (yyyy-mm-dd hh:mm) -
Nominal Cycle Interval -
 

Spatial Co-ordinates

Latitude 24.49835 N ( 24° 29.9' N )
Longitude 66.20922 W ( 66° 12.6' W )
Positional Uncertainty Unspecified
Minimum Sensor Depth 4.6 m
Maximum Sensor Depth 111.4 m
Minimum Sensor Height 5024.0 m
Maximum Sensor Height 5130.8 m
Sea Floor Depth 5135.4 m
Sensor Distribution Unspecified -
Sensor Depth Datum Unspecified -
Sea Floor Depth Datum Instantaneous - Depth measured below water line or instantaneous water body surface
 

Parameters

BODC CODE Rank Units Short Title Title
ADEPZZ01 1 Metres DepBelowSurf Depth below surface of the water body
BOTTFLAG 1 Dimensionless C22_flag Sampling process quality flag (BODC C22)
FIRSEQID 1 Dimensionless FireSeqNo Bottle firing sequence number
NTRZLWTX 1 Micromoles per litre NO3+NO2_Lwnano Concentration (nM sensitivity) of nitrate+nitrite {NO3+NO2} per unit volume of the water body [dissolved plus reactive particulate phase] by colorimetric autoanalysis with liquid waveguide capilliary cell
PHOSLWTX 1 Micromoles per litre PO4_Lwnano Concentration (nM sensitivity) of phosphate {PO43- CAS 14265-44-2} per unit volume of the water body [dissolved plus reactive particulate phase] by colorimetric autoanalysis with liquid waveguide capilliary cell
SAMPRFNM 1 Dimensionless SampRef Sample reference number
 

Definition of Rank

  • Rank 1 is a one-dimensional parameter
  • Rank 2 is a two-dimensional parameter
  • Rank 0 is a one-dimensional parameter describing the second dimension of a two-dimensional parameter (e.g. bin depths for moored ADCP data)

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 have a capacity between 1.7 and 30 L, while Lever Action bottles have a capacity between 1.7 and 12 L. Reversing thermometers may be attached to a spring-loaded disk that rotates through 180° on bottle closure.

RAPID Cruise D346 discrete nutrient sampling

Originator's data acquisition and analysis

Inorganic and total nutrients

Seawater was collected for analysis of micro-molar concentrations of dissolved nutrients; nitrate and nitrite, phosphate and silicate. Samples for inorganic nutrient analysis were collected directly into either 30 mL plastic pots or 60 mL Sterilin pots. 60 mL pots were used for collection of seawater for total nutrient analysis. The pots were rinsed with sample water at least three times before drawing the sample. When required, samples were stored in a fridge at approximately 4°C until analysis.

In general, analyses were started within 1-4 hours of sample collection using a segmented continuous-flow Skalar Sanplus autoanalyser according to standard colormetric techniques described by Kirkwood (1996). The only exception to this was the increase of the pump rate by a factor of 1.5 through the phosphate, improving the reproducibility and peak shape of the results.

5 µmol L -1 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), which was also used as diluent for the analyses.

Total nutrients (total nitrogen (TN) and total phosphorus (TP)) were measured as nitrate and phosphate after photo-oxidation for 2 hours using a Metrohm 705 digester (Sanders and Jickells, 2002). The oxidation efficiency of the method was monitored using a Guanosine standard at two different N and P concentrations; i) 2 and 5 µmol L -1 for nitrogen, ii) 0.4 and 1 µmol L -1 for phosphorus, which produced i) 2±0.3 and 4.1±0.8 (efficiency higher than 80%) and ii) 0.2±0.3 and 0.8±0.2 (efficiency higher than 50%) respectively. The UV systems were installed inside the fume hood of the chemistry lab and a flow meter was attached in order to monitor the water flow for cooling.

At the start of the cruise all samples from all stations were UV oxidised in duplicates. However, when the two UV units started to fail, this caused a delay in the analysis process resulting in a large backlog of samples.

Ideally, the total nutrients should have be analysed together with their respective inorganic fraction in the same autoanalyser run, but the large backlog prompted a run of all inorganic nutrient samples immediately. The total nutrients were run as soon they became available upon UV oxidation (from Station 1 to Station 39). This meant analysing total nutrients in separate runs.

The number of samples being analysed for total nutrient concentrations was reduced to every third station. From station 39 and starting with station 42, one out of three casts were thus sampled for total nutrients. Whenever a Niskin bottle misfired, the available space on the UV unit rack was used for either a replicate or for the analysis of a Guanosine standard.

Once the backlog was cleared and the time between stations increased, it was decided that samples for total nutrient analysis should be taken from all casts again. However, this was not possible, due to the continuous failure of the UV systems. Repeats of whole profiles were also run for a number of stations to check the reliability of the UV digester units and accuracy of the total nutrient concentrations.

Inorganic nitrate and phosphate at nanomolar concentrations

A gas-segmented continuous-flow colorimetric method was used for both phosphate and nitrate. The chemical methods are described by Grasshoff et al., (1983). The autoanalyser is coupled with liquid waveguide capillary cells (LWCC) to achieve nanomolar levels of detection (Patey et al. 2008).

Blanks were measured with Milli-Q and low nutrients seawater (LNSW). Prior to this, the LNSW was aged for several months in the lab at room temperature and with the presence of light. Standards were measured in Milli-Q and LNSW to correct for the salt effect from the seawater matrix.

Samples were drawn from Niskin bottles on the CTD into 10% HCl clean 60 ml bottles and kept refrigerated at approximately 4 o C until analysis. Analysis was undertaken on a modified Burkard Autoanalyser with one main peristaltic pump and reaction channels, one for phosphate and one for nitrate.

The detection cells were Liquid Core Waveguide Capillary Cells (LWCC) of 2 m in length. Spectrophotometric detection was achieved using tungsten lamps as light sources and two spectrometers. These devices were linked with fiber-optic connections.

Data acquisition was conducted in two steps using Spectrasuite software. First, the spectrum of the coloured complex provided a value of the signal intensity for each wavelength. Secondly, the absorbance of the signal was measured for the wavelength of interest for each compound. The selected wavelengths for nitrate and phosphate are respectively 540 nm and 710 nm.

Some problems were encountered with the analyser. These were:

1. The software's capability to read both channels simultaneously. The software did not support the function of being given two references, one for each channel. Therefore, a reference monitor was required for the second acquisition.

2. Contamination of samples in the lab. This problem had been anticipated, so a bag, flushed with oxygen-free nitrogen, was successfully set around the sampler to prevent any contamination from the air. The first sample read was repeated at the end of the run to ensure there was no contamination.

Further details can be found in the D346 cruise report (King et al., 2012).

References cited

Grasshoff, K., Ehrhardt, M., Kremling, K. (1983). Methods of Seawater Analysis, Verlag Chemie, Weinheim.

King, B.A., Hamersley, D. R. C (ed.) (2012) RRS Discovery Cruise 346 , 05 Jan - 19 Feb 2010. The 2010 transatlantic hydrography section at 24.5°N. Southampton, UK, National Oceanography Centre, Southampton, 177pp. (National Oceanography Centre Southampton Cruise Report).

Kirkwood, D. (1996). Nutrients: Practical notes on their determination in seawater. ICES Techniques in Marine Environmental, 17, 1-25.

Patey, M. D., Rijkenberg, M.J.A., Statham, P.J., Mowlem, M., Stinchcombe, M.C., Achterberg, E.P. (2008). Determination of nitrate and phosphate in seawater at nanomolar concentrations, TrAC Trends in Analytical Chemistry, 27 (2), 169-182.

BODC data processing procedures

The data were supplied in MSTAR format for the nitrate, phosphate, silicate, total nitrogen, total phosphorus, dissolved organic nitrate and dissolved organic phosphorus variables and converted to ASCII. Data for nanomolar concentrations of nitrate and phosphate were supplied to BODC in a csv spreadsheet. Units were converted, if necessary, to the BODC standard parameter units. The data were then loaded into a database under the ORACLE Relational Database Management System without modification.

Data that lay outside the permitted range for the parameter code were flagged suspect with an 'M' flag by BODC.

Content of data series

Originator's parameter Description Units BODC parameter code Units Comments
totnit Nitrate+Nitrite µmol kg -1 NTKGAATX µmol kg -1 -
phos Phosphate µmol kg -1 PHKGAATX µmol kg -1 -
silc Silicate µmol kg -1 SLKGAATX µmol kg -1 -
tn Total nitrogen µmol kg -1 NTAAKGD1 µmol kg -1 -
tp Total phosphorus µmol kg -1 TPHSKG01 µmol kg -1 -
nitrate (nM) Nanomolar concentrations of nitrate nM NTRZLWTX µmol l -1 Unit conversion: *0.001
phosphate (nM) Nanomolar concentrations of phosphate nM PHOSLWTX µmol l -1 Unit conversion: *0.001
DON Dissolved organic nitrogen µmol kg -1 MDMAP008 µmol kg -1 -
DOP Dissolved organic phosphorus µmol kg -1 ORGPDSZZ µmol kg -1 -

Data quality

Quality control flags that were used by the originator have been mapped to BODC flags as shown below:

Originator flag Description BODC flag Comments
2 Good ' ' -
3 Questionable L -
4 Bad L -
6 Duplicate - -
9 Not sampled - Not loaded into database

Project Information

Rapid Climate Change (RAPID) Programme

Rapid Climate Change (RAPID) is a £20 million, six-year (2001-2007) programme of the Natural Environment Research Council (NERC). The programme aims to improve our ability to quantify the probability and magnitude of future rapid change in climate, with a main (but not exclusive) focus on the role of the Atlantic Ocean's Thermohaline Circulation.

Scientific Objectives

Projects

Overall 38 projects have been funded by the RAPID programme. These include 4 which focus on Monitoring the Meridional Overturning Circulation (MOC), and 5 international projects jointly funded by the Netherlands Organisation for Scientific Research, the Research Council of Norway and NERC.

The RAPID effort to design a system to continuously monitor the strength and structure of the North Atlantic Meridional Overturning Circulation is being matched by comparative funding from the US National Science Foundation (NSF) for collaborative projects reviewed jointly with the NERC proposals. Three projects were funded by NSF.

A proportion of RAPID funding as been made available for Small and Medium Sized Enterprises (SMEs) as part of NERC's Small Business Research Initiative (SBRI). The SBRI aims to stimulate innovation in the economy by encouraging more high-tech small firms to start up or to develop new research capacities. As a result 4 projects have been funded.


Data Activity or Cruise Information

Cruise

Cruise Name D346
Departure Date 2010-01-05
Arrival Date 2010-02-19
Principal Scientist(s)Brian A King (National Oceanography Centre, Southampton)
Ship RRS Discovery

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:

Flag Description
Blank Unqualified
< Below detection limit
> In excess of quoted value
A Taxonomic flag for affinis (aff.)
B Beginning of CTD Down/Up Cast
C Taxonomic flag for confer (cf.)
D Thermometric depth
E End of CTD Down/Up Cast
G Non-taxonomic biological characteristic uncertainty
H Extrapolated value
I Taxonomic flag for single species (sp.)
K Improbable value - unknown quality control source
L Improbable value - originator's quality control
M Improbable value - BODC quality control
N Null value
O Improbable value - user quality control
P Trace/calm
Q Indeterminate
R Replacement value
S Estimated value
T Interpolated value
U Uncalibrated
W Control value
X Excessive difference

SeaDataNet Quality Control Flags

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

Flag Description
0 no quality control
1 good value
2 probably good value
3 probably bad value
4 bad value
5 changed value
6 value below detection
7 value in excess
8 interpolated value
9 missing value
A value phenomenon uncertain