Metadata Report for BODC Series Reference Number 550930

• 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

Guildline 8705 CTD

The 8705 CTD is a conductivity-temperature-pressure profiler designed for marine applications down to depths of 6000 m. The instrument includes an anodised aluminium tube with a steel cage to protect the temperature and conductivity sensors and a urethane cap to protect the pressure sensor.

Specifications

* Conductivity specifications are given in terms of equivalent salinity

Further details can be found in the manufacturer's specification sheet.

RV Cirolana 7B/1993 (JONUS Exercise 18) CTD Data Documentation

Introduction

This cruise used the Guildline CTD s/n 45056 at the JONUS stations. The following is a presentation of the data returned from stations 10-169.

Data Collection

53 CTD profiles were obtained using the Guildline CTD during the cruise.

Reversing thermometers were used to measure water temperature and samples were collected for salinity analysis.

Left and right thermometer temperatures were available on 29 occasions. 4 pairs of thermometer results were not used, as their difference was <0.04.

All thermometers were graduated at 0.02 °C intervals and a comparison of the differences is as follows:

Thus, 79% of the differences lie within the range 0.02 °C, the thermometer scale graduation.

Duplicate water samples were collected on 3 occasions for analysis with a Guildline salinometer.

On 96 other stations, only 1 water sample salinity was available. The distribution of the differences is as follows:

Thus, 100% of the differences lie within 0.002.

Sensor Calibration for Guildline CTD

Pressure

The laboratory calibration of August 1992, sensor at 16 °C, was used to correct the Guildline CTD pressure sensor:

P(cor) = P(ctd) - 1.4 db

Temperature

Fig. 1 shows the differences between the (mean) thermometer and uncorrected CTD temperature when the left/right thermometer difference was less than or equal to 0.04 °C (29 occasions). The mean difference calculated for the 29 instances when the left and right thermometers themselves differed by less than or equal to 0.04 was 0.023 °C.

This compares with the laboratory pre-cruise calibration of May 1993 which estimated the CTD correction to be approximately 0.007 °C at the

temperatures encountered during the cruise. The agreement between

thermometer and CTD during this cruise was not as good as usual. The sensor was corrected using the laboratory pre-cruise calibration coefficients:

T(cor) = T(ctd) + dT

dT = a*T(ctd)*T(ctd) + b*T(ctd) + c

where:

a = 5.24713e-5
b = -9.60448e-4
c = 8.809e-3

Fig. 2 shows the differences between these 29 thermometer and CTD temperatures after the latter have been corrected. The mean difference is 0.016 °C and all differences lie within ±0.03 °C, supporting the belief that if the thermometers are accurate to ±0.02 °C then the CTD temperatures are accurate to ±0.01 °C.

Salinity

Fig. 3 shows the difference between the water sample salinity as measured with the Guildline salinometer and that derived from the CTD before any calibrations have been applied to the latter's sensors. Note that 2 data values have been removed prior to plotting Fig. 3 because the differences were large suggesting either an erroneous CTD value or water sample salinity.

Fig. 3 suggests that the CTD has a tendency to over-estimate salinity.

Fig. 4 shows the ratio of CTD:Water sample conductivity ratio after the CTD pressure and temperature sensors have been corrected using the above coefficients.

A set of coefficients have been derived to calibrate the CTD conductivity sensor, using a least square fit between the ratio of water sample and CTD conductivity and the CTD temperature and pressure. Station 30 was in a river estuary and not used to determine the conductivity calibration.

CR(cor) = CR(ctd)*{a*T(cor) + b*P(cor) + c}

where:

T(cor) and P(cor) are the corrected CTD temperature and pressure
a = 4.04132793e-05
b = 3.98584338e-06
c = 0.999104984

RMS salinity difference between water sample and corrected CTD = 0.008 with the number of data values = 96

Fig. 5 illustrates how effective the CTD conductivity and derived salinity have been corrected. The tendency of the CTD to over- estimate salinity has been overcome.

The histograms in Fig. 6 show how well the CTD conductivity is corrected since the upper frame has been derived after the CTD temperature and pressure have been corrected, but before the CTD conductivity calibration has been applied.

If it is assumed that the salinometer is accurate to 0.006 and the CTD salinity to 0.01, then differences between ±0.016 are acceptable. 94% of the values lie within this range after the calibrations have been applied.

Transmission/Suspended Load

A 25 cm path length transmissometer (s/n 198) was fitted to the CTD rosette and calibrated in terms of suspended load (mg/1) by comparing the logged %transmission with laboratory determinations of suspended load.

suspended load = a*loge(%Trans) + b

Coastal stations:- (10-92)

where a = -9.67 and b = 36.52

North sea stations:- (93 onwards)

where a = -10.1 and b = 38.04

General Data Screening carried out by BODC

BODC screen both the series header qualifying information and the parameter values in the data cycles themselves.

Header information is inspected for:

• Irregularities such as unfeasible values
• Inconsistencies between related information, for example:
  • Times for instrument deployment and for start/end of data series
  • Length of record and the number of data cycles/cycle interval
  • Parameters expected and the parameters actually present in the data cycles
• Originator's comments on meter/mooring performance and data quality

Documents are written by BODC highlighting irregularities which cannot be resolved.

Data cycles are inspected using time or depth series plots of all parameters. Currents are additionally inspected using vector scatter plots and time series plots of North and East velocity components. These presentations undergo intrinsic and extrinsic screening to detect infeasible values within the data cycles themselves and inconsistencies as seen when comparing characteristics of adjacent data sets displaced with respect to depth, position or time. Values suspected of being of non-oceanographic origin may be tagged with the BODC flag denoting suspect value; the data values will not be altered.

The following types of irregularity, each relying on visual detection in the plot, are amongst those which may be flagged as suspect:

• Spurious data at the start or end of the record.
• Obvious spikes occurring in periods free from meteorological disturbance.
• A sequence of constant values in consecutive data cycles.

If a large percentage of the data is affected by irregularities then a Problem Report will be written rather than flagging the individual suspect values. Problem Reports are also used to highlight irregularities seen in the graphical data presentations.

Inconsistencies between the characteristics of the data set and those of its neighbours are sought and, where necessary, documented. This covers inconsistencies such as the following:

• Maximum and minimum values of parameters (spikes excluded).
• The occurrence of meteorological events.

This intrinsic and extrinsic screening of the parameter values seeks to confirm the qualifying information and the source laboratory's comments on the series. In screening and collating information, every care is taken to ensure that errors of BODC making are not introduced.

Project Information

Joint Nutrient Study I (JoNuS)

Concerns by the scientific community about the impact of nutrient inputs to the sea; a lack of information on inputs from the UK and on the spatial and temporal distribution and cycling of nutrients in UK waters provided the impetus for the JoNuS project.

The project sought to quantify the input of nitrogen, phosphorus and silicon from UK estuaries to the North Sea through a good understanding of the estuarine processes that control the flow of these nutrients. It focussed on the Great Ouse/Wash and the Humber outflows. Its specific objectives were:

• To measure the fluxes of nutrient elements (N, P, Si) through selected major estuaries on a quantitative annual basis in order to determine the net input to the sea resulting from gross river inputs.
• To quantify the processes controlling the fluxes of nutrients through estuaries.

The Centre for Environment, Fisheries and Aquaculture Science (CEFAS) hosted the project, which involved scientists from CEFAS, the University of East Anglia, the University of Essex, the Plymouth Marine Laboratory and the National Rivers Authority (now the Environment Agency). It was funded by the then Ministry of Agriculture, Fisheries and Food (MAFF) and the Department of Environment, now the Department of Environment, Food and Rural Affairs (Defra).

The project ran from April 1990 to March 1995, with marine field data collection between May 1990 and December 1993. Data collection involved ship based surveys which were complemented by estuarine transects and specific process studies.

Initially, the surveys were on a quarterly basis up to October 1992, however monthly surveys were carried out during 1993. During this intensive survey period, the programme focused on the Great Ouse/Wash; with a continuing, but lower level, of activity devoted to the Humber. An additional multi-project cruise, carried out in January 1995, also complemented the JoNuS data set. Further details of the JoNuS I cruises are provided below:

Data Activity or Cruise Information

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: