Metadata Report for BODC Series Reference Number 1351885

• 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

Public domain data

These data have no specific confidentiality restrictions for users. However, users must acknowledge data sources as it is not ethical to publish data without proper attribution. Any publication or other output resulting from usage of the data should include an acknowledgment.

The recommended acknowledgment is

"This study uses data from the data source/organisation/programme, provided by the British Oceanographic Data Centre and funded by the funding body."

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.

CD173 Discrete Nutrient Sampling Document

Originator's Protocol for Data Acquisition and Analysis

Water samples were taken during RRS Charles Darwin cruise CD173 which was conducted in the Celtic Sea from 15 July 2005 to 06 August 2005. 706 samples were collected during 84 casts, from rosette bottles fired at various depths throughout the water column. The collection depths were chosen on the basis of real-time fluoresence and temperature traces. With 25 exceptions, single samples were taken from rosette bottles. For the 25 exceptions, duplicate samples were taken and analysed.

All measurements for nitrate, phosphate and silicate were made on board using standard colorimetric methods (Grasshoff et al. 1983) with a Skalar AAII Autoanalyser.

References Cited

Grasshoff K. M., Erhardt M. K. and Kremling K., 1983. Methods of seawater analysis. Verlag-Chemie.

BODC Data Processing Procedures

The nutrient data were supplied to BODC in Microsoft Excel format. Values were extracted from this and saved in ASCII format prior to being loaded into the BODC Samples Database under the ORACLE Relational Database Management System. Methodology and units were checked against information held in the BODC parameter dictionary and an appropriate parameter code was attributed to each variable. Data that were considered unrealistic were flagged suspect. For duplicate samples, the mean concentration of each parameter from both samples was calculated and stored in the database, along with the corresponding standard deviation.

Content of data series

Comments

The data supplied to BODC included numerous values which were below the limit of detection quoted by the Data Originator (0.1 µmol l^-1) for the Skalar AAII Autoanalyser. These values were replaced with the instrument detection limit value and flagged accordingly.

For seven of the 25 duplicate samples, the concentrations of both replicates for NO₃+NO₂ and for PO₄ were below the limit of detection. These replicates were not averaged and the value loaded to the database was the instrument detection limit. The values were flagged accordingly.

The Data Originator supplied concentrations from casts CTD029, CTD030, CTD032, CTD052 and CTD058 taken at 2 m depth. The CTD logs and electronic bottle firing records for these casts however had no record of bottles being fired at these depths. As a result of this discrepancy, these concentrations were not loaded into the database but are available from BODC on request.

For 30 of the 84 casts, multiple bottles were fired at the same depths. The Data Originator supplied the data linked by cast and depth, but not against specific bottles. BODC therefore took the decision to arbitrarily link the samples in the order they were supplied in the original spreadsheet to the bottles fired at that depth in sequence e.g. first sample at 25 m depth for cast CTD011 linked to bottle 14, second sample to bottle 15, third to bottle 16 and so on). The total number of samples which were linked in this manner was 119. The user should be aware that this linkage is arbitrary and may not be correct.

Project Information

Physical-Biological Control of New Production within the Seasonal Thermocline

This project was a NERC responsive-mode project which was co-funded by the Defence Science and Technology Laboratory and ran from 2003 to 2006. The key institutes and scientists involved were:

Research Aim

The main aim of this research was to investigate the generation and dissipation of turbulence in the thermocline, and to quantify how the resulting mixing (supplying nutrients and controlling the light experienced by the algae) affected the growth of phytoplankton within the sub-surface chlorophyll maximum (SCM).

Research Objectives

The objective of the research was to test the general hypothesis that, in seasonally-stratified shelf waters, temporal and spatial variability of the rate of 'new' production is determined by the degree of coupling between physical and biological processes within the seasonal thermocline. In particular it has been suggested that physiological adaptation by phytoplankton making up the subsurface chlorophyll maximum drives a biological pump for extracting nitrate from the bottom mixed layer that is sensitive to internal mixing and to external climatological factors.

Research Approach

The sampling and experimental strategy was based on established methods for obtaining compatible, high-resolution vertical profiles (alternate CTD and FLY) and sections (SeaSoar) of physical, chemical, and biological parameters, allowing quantification of vertical fluxes and primary production on tidal and internal wave time scales. The cruise schedule (with associated mooring deployments) for the project is below.

Cruise Schedule

Moorings

^* = metres above seabed

Project Outcomes

The main products of the research were:

• The first large scale interdisciplinary study of the dynamic processes that determine the properties of the SCM in NW European shelf waters.
• Substantive advances in quantifying internal mixing in NW European shelf seas, and in understanding how primary production is controlled by this small-scale turbulence.
• New parameterisations for internal vertical mixing, and the response of primary production, for use in coupled numerical models.
• Improved capability for estimating primary productivity in stratified waters by satellite remote sensing (ocean colour, sea surface temperature, wind mixing etc.)
• An overall development of our understanding of the dynamics of ecosystems that support important fisheries, and of our abilities in predicting ecological and biogeochemical responses to variations and changes in the climate of the marine environment.

Data Activity or Cruise Information

Data Activity

BODC Sample Metadata Report for CD173_CTD_CTD028

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: CD173_CTD_CTD028

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

If you are interested in these series, please be aware we offer a multiple file download service. Should your credentials be insufficient for automatic download, the service also offers a referral to our Enquiries Officer who may be able to negotiate access.