Metadata Report for BODC Series Reference Number 976365


Metadata Summary

Data Description

Data Category CTD or STD cast
Instrument Type
NameCategories
Neil Brown MK3 CTD  CTD; water temperature sensor; salinity sensor; dissolved gas sensors
Instrument Mounting research vessel
Originating Country United Kingdom
Originator Prof Andy Watson
Originating Organization Plymouth Marine Laboratory (now Marine Biological Association of the UK)
Processing Status banked
Project(s) WOCE
UK WOCE
 

Data Identifiers

Originator's Identifier CTD018
BODC Series Reference 976365
 

Time Co-ordinates(UT)

Start Time (yyyy-mm-dd hh:mm) 1992-05-15 19:15
End Time (yyyy-mm-dd hh:mm) -
Nominal Cycle Interval 1.0 decibars
 

Spatial Co-ordinates

Latitude 25.59667 N ( 25° 35.8' N )
Longitude 28.30000 W ( 28° 18.0' W )
Positional Uncertainty 0.0 to 0.01 n.miles
Minimum Sensor Depth 9.94 m
Maximum Sensor Depth 487.24 m
Minimum Sensor Height 4785.96 m
Maximum Sensor Height 5263.26 m
Sea Floor Depth 5273.2 m
Sensor Distribution Variable common depth - All sensors are grouped effectively at the same depth, but this depth varies significantly during the series
Sensor Depth Datum Instantaneous - Depth measured below water line or instantaneous water body surface
Sea Floor Depth Datum Chart reference - Depth extracted from available chart
 

Parameters

BODC CODE Rank Units Short Title Title
POTMCV01 1 Degrees Celsius WC_Potemp Potential temperature of the water body by computation using UNESCO 1983 algorithm
PRESPR01 1 Decibars Pres_Z Pressure (spatial co-ordinate) exerted by the water body by profiling pressure sensor and corrected to read zero at sea level
PSALST01 1 Dimensionless P_sal_CTD Practical salinity of the water body by CTD and computation using UNESCO 1983 algorithm
SIGTPR01 1 Kilograms per cubic metre SigTheta Sigma-theta of the water body by CTD and computation from salinity and potential temperature using UNESCO algorithm
TEMPST01 1 Degrees Celsius WC_temp_CTD Temperature of the water body by CTD or STD
 

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

Neil Brown MK3 CTD

The Neil Brown MK3 conductivity-temperature-depth (CTD) profiler consists of an integral unit containing pressure, temperature and conductivity sensors with an optional dissolved oxygen sensor in a pressure-hardened casing. The most widely used variant in the 1980s and 1990s was the MK3B. An upgrade to this, the MK3C, was developed to meet the requirements of the WOCE project.

The MK3C includes a low hysteresis, titanium strain gauge pressure transducer. The transducer temperature is measured separately, allowing correction for the effects of temperature on pressure measurements. The MK3C conductivity cell features a free flow, internal field design that eliminates ducted pumping and is not affected by external metallic objects such as guard cages and external sensors.

Additional optional sensors include pH and a pressure-temperature fluorometer. The instrument is no longer in production, but is supported (repair and calibration) by General Oceanics.

Specifications

These specification apply to the MK3C version.

Pressure Temperature Conductivity
Range

6500 m

3200 m (optional)

-3 to 32°C 1 to 6.5 S cm -1
Accuracy

0.0015% FS

0.03% FS < 1 msec

0.0005°C

0.003°C < 30 msec

0.0001 S cm -1

0.0003 S cm -1 < 30 msec

Further details can be found in the specification sheet .

RRS Charles Darwin 68 CTD Data Documentation

Introduction

CTD profile data are presented from the North Atlantic Tracer Release Experiment cruise Charles Darwin 68 as reported by Watson & Ledwell et al. (1992).

Instrumentation and Methodology

Instrumentation Summary

The CTD profiles were taken with a Neil Brown Systems MkIII CTD (s/n 01-1195). This was mounted in a sled custom built by WHOI along with a rosette multisampler (12 bottle 10-litre type manufactured by General Oceanics) and 1.2 litre Niskin bottles. The CTD was fitted with a pressure sensor, conductivity cell, and a platinum resistance thermometer. 4 reversing thermometers were also attached to the sled.

The sled was at the centre of a much larger vertical array of custom designed water samplers (for SF 6 ), interspersed with SEACAT CTDs. The whole array was towed through the water for a period of several hours.

Data Acquisition

Each sampler tow was preceded by a downcast to 500m at about 25m/min, and was followed by an upcast from 500m at roughly the same speed. Since the ship was generally moving at about 1kt (30m/min) the descent and ascent angles are about 45° from the vertical.

A total of 59 casts were conducted (01 - 59). Casts 01 - 15 were test casts and casts to determine background SF6 concentrations. Up to 7 salinity samples and 4 reversing thermometer values were acquired during each cast for the calibration of the CTD.

Data Processing

The raw data have had spikes near the rosette trips removed. There were still obvious spikes of noise in the data. The data from the CTD descents and ascents were interpolated to standard levels every metre from 10m to 500m, where data were available. These were then averaged at the 1m intervals.

Temperature and Pressure

The MkIII CTD was calibrated for temperature and pressure on shore prior to departure. The temperature calibration was checked throughout the cruise with four digital reversing thermometers mounted on the sampling sled. However, the strong temperature gradients and the mismatch in time and space between the reversing thermometers and the CTD probes resulted in rms noise of around 0.090°C. Therefore the shore-based calibrations, which should stand to better than 0.004°C were relied upon for temperature.

Salinity

Salinity calibrations were also performed throughout the cruise, with samples from the 5-litre Niskin bottles during the background casts and from 1.2-litre Niskin bottles mounted horizontally on the sampling sled during the tows. They showed a consistent salinity error of -0.022psu for the MkIII system for the part of the water column sampled. This correction was applied in processing the CTD data. The processed CTD data are considered as accurate as possible; no post-cruise adjustment of the data was conducted.

BODC Data Processing

No further calibrations were applied to the data received by BODC. BODC were mainly concerned with the screening and banking of the data.

The CTD data were received as 1db averaged pressure sorted down cast data. Parameters were pressure (dbar), temperature (its-90) and salinity (pss-78).

The data were converted into the BODC internal format (PXF) to allow the use of in-house software tools, notably the graphics editor. Spikes in the data were manually flagged 'suspect' by modification of the associated quality control flag. In this way none of the original data values were edited or deleted during quality control.

Very little flagging was required for these data.

Once screened, the CTD data were loaded into a database under the Oracle relational database management system. The start time stored in the database is the tow deployment time, and the end time is the start time + 60 minutes. 1 day was subtracted from all these times after comparison with the cruise report and navigation.

References

Watson, A.J. & Ledwell, J.R. et al. (1992). RRS Charles Darwin Cruise 68, The North Atlantic Tracer Release Experiment (NATRE): First Sampling Leg. Plymouth Marine Laboratory, Cruise Report.


Project Information

World Ocean Circulation Experiment (WOCE)

The World Ocean Circulation Experiment (WOCE) was a major international experiment which made measurements and undertook modelling studies of the deep oceans in order to provide a much improved understanding of the role of ocean circulation in changing and ameliorating the Earth's climate.

WOCE had two major goals:


UK WOCE

The UK made a substantial contribution to the international World Ocean Circulation Experiment (WOCE) project by focusing on two important regions:

  1. Southern Ocean - links all the worlds oceans, controlling global climate.
  2. North Atlantic - directly affects the climate of Europe.

A major part of the UK effort was in the Southern Ocean and work included:

In the North Atlantic the UK undertook:

Satellite ocean surface topography, temperature and wind data were merged with in situ observations and models to create a complete description of ocean circulation, eddy motion and the way the ocean is driven by the atmosphere.

The surveys were forerunners to the international Global Ocean Observing System (GOOS). GOOS was later established to monitor annual to decadal changes in ocean circulation and heat storage which are vital in the prediction of climate change.


Data Activity or Cruise Information

Cruise

Cruise Name CD68
Departure Date 1992-05-08
Arrival Date 1992-06-08
Principal Scientist(s)Andrew J Watson (Plymouth Marine Laboratory)
Ship RRS Charles Darwin

Complete Cruise Metadata Report is available here


Fixed Station Information

Fixed Station Information

Station NameWOCE Atlantic Area 10 (AR10)
CategoryOffshore area
Latitude27° 0.00' N
Longitude32° 30.00' W
Water depth below MSL

World Ocean Circulation Experiment (WOCE) Atlantic Area 10 (AR10)

WOCE was a major international experiment which made measurements and undertook modelling studies of the deep oceans in order to provide a much improved understanding of the role of ocean circulation in changing and ameliorating the Earth's climate. WOCE established numerous areas and repeat sections in the Atlantic Ocean as illustrated in the map below.

BODC image

The AR10 'Beta-triangle' experiments where centred at 27.0°N, 32.5°W in the southwestern end of the North Atlantic subtropical gyre, with the area occupied between May 1992 to May 1993. A table of all AR10 cruises is presented below:

Cruise Cruise dates Country
Charles Darwin 68 1992-05-08 to 1992-06-08 UK
Oceanus 1992-09-21 to 1992-10-21 USA
Oceanus 1992-10-29 to 1992-11-16 USA
Hudson 1993-04-05 to 1993-05-14 Canada
Charles Darwin 78 1993-04-22 to 1993-05-24 UK

Other Series linked to this Fixed Station for this cruise - 976224 976236 976248 976261 976273 976285 976297 976304 976316 976328 976341 976353 976377 976389 976390 976408 976421 976433 976445 976457 976469 976470 976482 976494 976501 976513 976525 976537 976549 976550 976562 976574 976586 976598 976605 976617 976629 976630 976642 976654 976666 976678 976691

Other Cruises linked to this Fixed Station (with the number of series) - CD78 (205)


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