Metadata Report for BODC Series Reference Number 1359887

• 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

RRS Discovery AMT15 (D284) - Continuous Underway Hydrographic Data Quality Report

Data Quality Report

There are no known quality issues with the data.

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

WET Labs WETStar Fluorometers

WET Labs WETStar fluorometers are miniature flow-through fluorometers, designed to measure relative concentrations of chlorophyll, CDOM, uranine, rhodamineWT dye, or phycoerythrin pigment in a sample of water. The sample is pumped through a quartz tube, and excited by a light source tuned to the fluorescence characteristics of the object substance. A photodiode detector measures the portion of the excitation energy that is emitted as fluorescence.

Specifications

By model:

All models:

Further details can be found in the manufacturer's specification sheet, and in the instrument manual.

Trimble 4000DS Global Positioning System receiver

The Trimble 4000DS Differential Surveyor is similar to the 4000RS (a Maxwell-based receiver that is oriented toward precision positioning applications. It is intended for use as a DGPS base station, generating RTCM-104 corrections). The 4000Ds can apply RTCM-104 corrections to the satellite data it receives in order to generate accurate position fixes in real time.

Falmouth Scientific Inc. Ocean Sensor Modules

FSI's individual sensor modules include an Ocean Conductivity Module (OCM), Ocean Temperature Module (OTM) and Ocean Pressure Module (OPM). All three use a low power micro-controller to collect, scale and transmit real-time data via RS-232 or RS-485.

* Higher accuracy available

For further details, see the manufacturer's specification sheet.

RRS Discovery AMT15 (D284) - Continuous Underway Hydrographic Instrumentation Document

Instrumentation

RRS Discovery AMT15 (D284) - Continuous Underway Hydrographic Processing Document

Originator's Data Processing

RRS Discovery is fitted with a central data logging system known as the ABC system. All available data streams from the ABC were collected. Most data streams have a one second sample interval with the exception of surfmet (30s) and ea500d1 (ping interval). ASCII listings were produced for all ABC system data streams.

The data archive was distributed to the PSO and BODC on DVD with compression of some datasets, notably processed CTD data and all the ABC data. A backup copy of the DVD was left onboard the ship, also one backup was taken back to UKORS. Approximately eight Gigabytes of data were acquired including processed data.

BODC Data Processing

Reformatting

Data from the full-resolution RVS files were transferred to BODC's NetCDF format (QXF) under the BODC Underway Data System (BUDS). This transfer involved reducing the data to 60 second intervals using averaging. Directional data were reduced by averaging using a unit circle.

Screening

Each data channel was inspected on a graphics workstation and any spikes or periods of dubious data were flagged. The power of the workstation software was used to carry out comparative screening checks between channels by overlaying data channels. A map of the cruise track was simultaneously displayed in order to take account of the oceanographic context.

Data processing, correction and calibration

Salinity

Salinity data from the thermosalinograph have been compared with calibrated surface CTD data to a depth of 20 m. This is usually done to a depth of 5 m, however, the CTD data down to ~15 m depth show a lot of variability. Different averaging depths (5 m, 10 m, 15 m and 20 m) were investigated and compared to the underway data. There was no significant difference in the long-wavelength salinity trend when averaging over the different depths compared to the underway data. Averaging to 20 m of CTD salinity data provided the best calibration and was therefore used. The underway data were averaged over the period of CTD deployments and standard deviations were used to check the quality of the data. The 79 samples showed the following relationship, which has been used to produce a calibrated salinity channel (PSALSG01).

PSALSG01 = 0.95856 * PSALSU01 + 1.39300 (BODC calibration 4175)

Temperature

TSG temperature was checked against the CTD temperature measurements averaged over the upper 5 m, 10 m, 15 m and 20 m of the water column. It was found that the best calibration was obtained with CTD measurements averaged over 10 m. Only CTD data points and underway records with a standard deviation lower than 0.01 deg.C over the duration of the cast were considered. A regression analysis was run on the data and, based on a total of 93 paired samples, the following calibration was derived.

TEMPSG01 = 1.00335 * TEMPSU01 - 0.14838 (BODC calibration 4177)

Chlorophyll

The fluorometer channel was calibrated by comparing the uncalibrated fluorometer output with chlorophyll concentration values extracted from samples collected from the ship's non-toxic water supply (N=88). Four different groups were identified, corresponding to the European Shelf, Northern Gyre, Equatorial Upwelling and the Southern Gyre and these were calibrated separately.

Group 1 (18/09/2004 to 27/09/2004, BODC calibration 4194):

CPHLUT01 = 0.996 * FVLTZZ01 - 0.065, R2=0.69

Group 2 (27/09/2004 to 02/10/2004, BODC calibration 4195):

CPHLUT01 = 4.035 * FVLTZZ01 - 0.456, R2=0.81

Group 3 (02/10/2004 to 23/10/2004, BODC calibration 4196):

CPHLUT01 = 0.485 * FVLTZZ01 - 0.041, R2=0.66

Group 4 (23/10/2004 to 27/10/2004, BODC calibration 4197):

CPHLUT01 = 0.849 * FVLTZZ01 - 0.077, R2=0.72

Residuals (extracted chlorophyll from the non-toxic minus calibrated fluorometer) follow a normal distribution and range between -0.10 and 0.20 mg chl m^-3 for chlorophyll concentrations ranging from 0.02 to 0.51 mg Chla m^-3. The largest variations occur over upwelling regions on the European shelf, North West Africa and near South Africa when extracted chlorophyll highs are not mirrored to the same extent in the fluorometer readings. Using four separate regressions provides a better fit to the extracted chlorophyll than using a single regression for the whole cruise. In fact, the sum of the squares of the residuals is 6 times lower when using 4 calibrations than when using a single calibration. However, this procedure has resulted in a small jump in CPHLUT01 on the 23/10/2004 where chlorophyll concentrations change rapidly and data from that date should be used cautiously.

Project Information

The Atlantic Meridional Transect - Phase 2 (2002-2006)

Who was involved in the project?

The Atlantic Meridional Transect Phase 2 was designed by and implemented by a number of UK research centres and universities. The programme was hosted by Plymouth Marine Laboratory in collaboration with the National Oceanography Centre, Southampton. The universities involved were:

• University of Liverpool
• University of Newcastle
• University of Plymouth
• University of Southampton
• University of East Anglia

What was the project about?

AMT began in 1995, with scientific aims to assess mesoscale to basin scale phytoplankton processes, the functional interpretation of bio-optical signatures and the seasonal, regional and latitudinal variations in mesozooplankton dynamics. In 2002, when the programme restarted, the scientific aims were broadened to address a suite of cross-disciplinary questions concerning ocean plankton ecology and biogeochemistry and the links to atmospheric processes.

The objectives included the determination of:

• how the structure, functional properties and trophic status of the major planktonic ecosystems vary in space and time
• how physical processes control the rates of nutrient supply to the planktonic ecosystem
• how atmosphere-ocean exchange and photo-degradation influence the formation and fate of organic matter

The data were collected with the aim of being distributed for use in the development of models to describe the interactions between the global climate system and ocean biogeochemistry.

When was the project active?

The second phase of funding allowed the project to continue for the period 2002 to 2006 and consisted of six research cruises. The first phase of the AMT programme ran from 1995 to 2000.

Brief summary of the project fieldwork/data

The fieldwork on the first three cruises was carried out along transects from the UK to the Falkland Islands in September and from the Falkland Islands to the UK in April. The last three cruises followed a cruise track between the UK and South Africa, only deviating from the traditional transect in the southern hemisphere. During this phase the research cruises sampled further into the centre of the North and South Atlantic Ocean and also along the north-west coast of Africa where upwelled nutrient rich water is known to provide a significant source of climatically important gases.

Who funded the project?

Natural Environment Research Council (NERC)

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: