Metadata Report for BODC Series Reference Number 952314

• 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

Transmissometer

Screening showed the attenuance record to be exceptionally clean whilst Challenger was working in the study area. However, the record was badly affected by bubble spikes on 11-12/02/1995 whilst the ship was sailing around Cornwall en route to Barry. Periods of data when the transmissometer was saturated by high sediment concentrations, when the instrument was being maintained and during interruptions to the non-toxic supply were also flagged suspect.

Nutrients

Numerous problems were experienced with the nutrient autoanalyser throughout the cruise. The silicate channel was particularly effected but all nutrient channels have undergone heavy flagging and should be used with caution.

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

Technicon AutoAnalyzer II (AAII)

The AAII is a segmented flow analyzer used for automated colorimetric analysis. The apparatus uses 2 mm diameter glass tubing and pumps reagents at flow rates of 2 to 3 ml s^-1, producing results at a typical rate of 30 to 60 samples per hour. The system comprises an autosampler, peristaltic pump, chemistry manifold a detector and a data acquisition software.

This instrument was replaced by the AA3 in 1997 which was upgraded to the AA3 HR systems in 2006.

Specifications

Aquatracka fluorometer

The Chelsea Instruments Aquatracka is a logarithmic response fluorometer. It uses a pulsed (5.5 Hz) xenon light source discharging between 320 and 800 nm through a blue filter with a peak transmission of 420 nm and a bandwidth at half maximum of 100 nm. A red filter with sharp cut off, 10% transmission at 664 nm and 678 nm, is used to pass chlorophyll-a fluorescence to the sample photodiode.

The instrument may be deployed either in a through-flow tank, on a CTD frame or moored with a data logging package.

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

SeaTech Transmissometer

Introduction

The transmissometer is designed to accurately measure the the amount of light transmitted by a modulated Light Emitting Diode (LED) through a fixed-length in-situ water column to a synchronous detector.

Specifications

• Water path length: 5 cm (for use in turbid waters) to 1 m (for use in clear ocean waters).
• Beam diameter: 15 mm
• Transmitted beam collimation: <3 milliradians
• Receiver acceptance angle (in water): <18 milliradians
• Light source wavelength: usually (but not exclusively) 660 nm (red light)

Notes

The instrument can be interfaced to Aanderaa RCM7 current meters. This is achieved by fitting the transmissometer in a slot cut into a customized RCM4-type vane.

A red LED (660 nm) is used for general applications looking at water column sediment load. However, green or blue LEDs can be fitted for specilised optics applications. The light source used is identified by the BODC parameter code.

Further details can be found in the manufacturer's Manual.

CH117_b Sea surface hydrography instrument details

Underway hydrography was recorded by a suite of instruments in the ship's flow-through system. Instrument details are given in the table below.

CH117_b Sea surface Hydrography Series Processing Notes

Nutrients

The nutrients were measured using a Technicon auto-analyser connected to the pumped seawater supply by a continuous filter block (Morris et al, 1978). The chemistries used were:

The chemistries used were:

The colorimeter outputs were logged by a Level A connected to the chart recorder inputs. The system was calibrated by running nutrient-depleted seawater washes to determine baseline and sets of four standards. Standards were generally run at least once per day.

The following processing procedures were adopted by BODC to convert the raw voltage streams into nutrient concentrations.

The data were then segmented into periods with constant colorimeter gain and baseline settings determined from the analyst's notes and examination of the chart records. The data were further segmented if non-linear baseline drift was observed. A baseline equation of the form:

Baseline voltage = Cycle number * coefficient_1 + coefficient_2

was determined for each segment and applied to give a standardised baseline of zero. The voltages measured whilst standards were being run were then used to construct calibration curves to convert raw voltages into nutrient concentrations.

These were then applied on a segment by segment basis to the data stream. All baseline and calibration equations were checked manually before they were used. Once concentrations had been calculated and checked, the custom flags for baselines and standards were changed to 'suspect'.

The data were subsequently quality controlled by inspection on a graphics workstation with particular attention paid to the concentrations obtained for the standards. Any data identified as suspect were flagged. These checks included comparative screening between the nutrient channels.

The nutrient time channels were adjusted to correct for the delay incurred whilst the sample passed through the complex plumbing of the auto-analyser. No salt corrections (corrections for difference in optical density between sample and standards) were applied as the standards were prepared in nutrient-depleted seawater.

The corrections applied were:

Due to the chemistry used for the nitrate analysis, interference from nitrite is inevitable. The nitrate channel has been processed throughout as nitrate+nitrite and no attempt has been made to correct for nitrite.

As a final processing step, small negative values in the data were converted to zero to prevent them causing problems for contouring software.

Chlorophyll

Chlorophyll was measured by a Chelsea Instruments Aquatracka fluorometer immersed in a light-tight pond. A common calibration was produced, which covers all three legs of Challenger 117. It was produced by regressing the natural logs of fluorometric extracted chlorophyll concentrations against the corresponding fluorometer voltages.

Chlorophyll concentrations were computed using the following equation:

Chlorophyll (mg m^-3) = exp (1.5475*fluorometer voltage - 2.0861) (R² = 9%)

The low statistical significance of this calibration is largely due to the very small data range covered by the calibration data set. The data from the three cruise legs were pooled in an attempt to improve matters, but with limited success. However, the calibration set covered the range of chlorophyll concentrations encountered on the cruise, resulting in acceptable calibrated fluorometer data.

Sea surface temperature and salinity

Temperature and salinity were measured using an autoranging TSG103 thermosalinograph. The temperature sensor was a thermistor in the non-toxic supply inlet manifold. Conductivity was measured by a unit in the ship's wet laboratory, which included a second thermistor to provide temperature for the computation of salinity.

The raw ADC counts were calibrated to give conductivity and two temperature channels based upon laboratory calculations by RVS. Salinity was computed from the housing temperature and conductivity using the UNESCO 1978 Practical Salinity Scale (Fofonoff and Millard, 1983).

The thermosalinograph was calibrated against surface values taken from the calibrated CTD. This was a curtailed cruise due to mechanical problems with the ship. Consequently, only four CTD casts were available for the thermosalinograph calibration.

The temperature offset was observed to be constant and a correction of +0.099 °C was applied to the whole cruise.

A number of discrete steps were seen in the salinity data. The cruise was split into four segments, each of which was calibrated separately. The salinity calibrations applied were:

30/01/95 17:02 to 10/02/95 07:13 Offset +0.112 PSU
10/02/95 07:14 to 10/02/95 13:12 Offset -0.193 PSU
10/02/95 13:13 to 11/02/95 16:05 Offset +0.112 PSU
11/02/95 16:06 to 12/02/95 15:07 Offset +0.661 PSU

Optical Attenuance and Sediment Load

Optical attenuance was measured using a SeaTech red light (661nm) transmissometer with a 25cm optical path length mounted in a light-tight box on the starboard deck fed from the non-toxic supply.

Transmissometer air readings made during the cruise (4.761V) were used to correct the transmissometer voltage to the manufacturer's specified air voltage (4.789V) by ratio. The voltages were then converted to attenuance to eliminate the influence of instrument path length using the equation:

Attenuance = -4.0 * log_e (voltage/5.0)

The transmissometer was calibrated in terms of sediment load using gravimetric data obtained on all legs of CH117 by filtering water through tared GF/F filters. The following calibration is based on the data obtained by the LOIS Core Team from PML:

SPM (mg/l) = (Attenuance - 0.3446) / 0.4151 (n=115 R²=93.7%)

References

Fofonoff, N.P. and Millard Jr., R.C. (1983). Algorithms for computation of fundamental properties of seawater. UNESCO Technical Papers in Marine Science 44.

Morris, A.W., Howland, R.J.M., and Bale, A.J. (1978). A filtration unit for use with continuous autoanalytical systems applied to highly turbid waters. Est. Coast. Mar. Sci. 6, 105-109.

CH117_b Sea surface Hydrography, Meteorology and Navigation Series

Instrumentation

Seawater was continuously pumped from the ship's hull (at a depth of about 4m). This is known as the ship's non-toxic supply. The thermosalinograph was fed through a small (100-litre) header tank. A large plastic tank on the starboard deck was fed directly from the non-toxic manifold and contained the transmissometer and fluorometer. Baffles in the tank ensured that a continuous flow was maintained over the instruments. The nutrient autoanalyser was fed from plastic tubing connected to taps on the non-toxic supply.

Calibration samples were either taken from the non-toxic tap on the wet laboratory sink or the thermosalinograph outlet.

Data Acquisition

Data logging and initial processing was handled by the RVS ABC system. The Level A sampling microcomputer digitised an input voltage, applied a time stamp and transferred the data via the Level B disk buffer onto the Level C where the data records were assembled into files.

Sampling rates varied from 10 seconds to several minutes.

The Level C included a suite of calibration software, which was used to apply initial calibrations to convert raw ADC counts into engineering units. At the end of the cruise, the Level C disk base was transferred to BODC for further processing.

BODC Data Processing Procedures

Data from the underway files were merged into a common file (the binary merge file) with a sampling interval of 30 seconds using time as the primary linking key. Data sampled at higher frequencies were reduced by averaging. Data logged as voltages (e.g. PAR, nutrients) were converted to engineering units.

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 undertake all possible comparative screening checks between channels.

Project Information

LOIS River-Atmosphere-Coast Study (LOIS - RACS)

Introduction

The Land-Ocean Interaction Study (LOIS) was a NERC research programme designed to study processes in the coastal zone. The Rivers, Atmosphere and Coasts Study (RACS) was a major component of LOIS that looked at land-sea interactions in the coastal zone and the major exchanges (physical, chemical and biological) between rivers and estuaries and the atmosphere. The study focused on the east coast of the UK from the Wash to the Tweed.

RACS included several sub-components

• BIOTA - A study of salt marshes of the Humber and Wash
• RACS (A) - An atmospheric chemistry study looking at air mass changes from the Wash into East Anglia
• RACS (C) - A study of the estuaries, coasts and coastal waters between Great Yarmouth and Berwick upon Tweed.
  1. The coastal oceangraphic survey
  2. The Humber estuarine study
  3. The Tweed estuarine study
  4. The Holderness experiment
• RACS (R) - A study of rivers that drain into the North Sea

RACS (A) was coordinated by the University of East Anglia and RACS (C) by the Plymouth Marine Laboratory.

RACS (A)

The bulk of the RACS (A) data set was collected during two field campaigns in the winter (October/November) of 1994 and the summer (May/June) of 1995. During these campaigns data were collected continuously from the University of East Anglia Atmospheric Observatory at Weybourne on the north Norfolk coast. An instrumented vessel was stationed offshore to provide a second sampling site to allow changes in a given air mass to be monitored. The Imperial College Jetstream research aircraft made one flight during each campaign to provide a link between the two surface stations. The Jetstream made four additional flights in 1996 and 1997.

RACS (C)

The coastal oceanographic survey

The coastal oceanographic data set was collected during a series of 17 RRS Challenger cruise legs. Most cruises covered two survey grids. One from Great Yarmouth to the Humber designed around the distribution of the sandbanks and a second simple zig-zag grid from the Humber to Berwick on Tweed. A large number of anchor stations, usually over one or two tidal cycles, were worked in the area of the Humber mouth or the Holderness coast.

The Humber estuarine study

The Humber estuarine data set was collected during a series of 33 campaigns on the Environment Agency vessels Sea Vigil and Water Guardian in the Humber, Trent and Ouse river systems at approximately monthly intervals between June 1993 and December 1996. Each campaign consisted of two or three one-day cruises. The tracks covered the estuary from the tidal limits of both Trent and Ouse to Spurn Point. Instrumental and sample data are available from a series of fixed stations that were sampled during every campaign.

The Tweed estuarine study

The Tweed estuarine data set was collected during a series of 13 campaigns using RV Tamaris in association with a rigid inflatable vessel at approximately monthly intervals between July 1996 and July 1997. Each campaign covered the tidal reaches of the River Tweed.

The Holderness experiment

The Holderness Experiment was designed to monitor the process of sediment transport along the Holderness coastline. It consisted of three moored instrument deployments during the winters of 1993-1994, 1994-1995 and 1995-1996. Mooring platforms were deployed at eight stations along two lines off the Holderness coast. A northerly and a southerly line of four stations each were used (N1 - N4 and S1 to S4) with the lowest numbers being inshore. Both lines were approximately perpendicular to the coast, although the S4 station lay to the south of the S line, off Spurn Head.

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: