Metadata Report for BODC Series Reference Number 1089100


Metadata Summary

Data Description

Data Category CTD or STD cast
Instrument Type
NameCategories
Sea-Bird SBE 911plus CTD  CTD; water temperature sensor; salinity sensor
Instrument Mounting lowered unmanned submersible
Originating Country United Kingdom
Originator Dr Jean-Baptiste Sallee
Originating Organization British Antarctic Survey
Processing Status banked
Project(s) DIMES
 

Data Identifiers

Originator's Identifier JR276_34
BODC Series Reference 1089100
 

Time Co-ordinates(UT)

Start Time (yyyy-mm-dd hh:mm) 2011-04-17 11:21
End Time (yyyy-mm-dd hh:mm) 2011-04-17 12:03
Nominal Cycle Interval 2.0 decibars
 

Spatial Co-ordinates

Latitude 62.66659 S ( 62° 40.0' S )
Longitude 78.00012 W ( 78° 0.0' W )
Positional Uncertainty 0.0 to 0.01 n.miles
Minimum Sensor Depth 2.97 m
Maximum Sensor Depth 2007.6 m
Minimum Sensor Height 2119.4 m
Maximum Sensor Height 4124.03 m
Sea Floor Depth 4127.0 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
ACYCAA01 1 Dimensionless Record_No Sequence number
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
PSALCC01 1 Dimensionless P_sal_CTD_calib Practical salinity of the water body by CTD and computation using UNESCO 1983 algorithm and calibration against independent measurements
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
TEMPS901 1 Degrees Celsius CTDTmp90 Temperature (ITS-90) 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

Instrument Description

CTD Unit and Auxiliary Sensors

Sensor Model Serial Number Calibration (UT) Comments
CTD underwater unit Sea-Bird 9plus underwater unit 09P - -
CTD deck unit Sea-Bird 11plus deck unit 11P-20391-0502 - -
Carousel 24 position pylon Sea-Bird 32 - - -
24x 10 litre water samplers Ocean Test Equipment BES-110L water samplers 1b - 24b - -
Pressure transducer Digiquartz pressure sensor 0707-89973 13/06/2007 -
Primary conductivity sensor Sea-Bird SBE4C conductivity sensor 04C-2248 25/06/2010 -
Secondary conductivity sensor Sea-Bird SBE4C conductivity sensor 04C-2813 20/07/2010 -
Primary temperature sensor Sea-Bird SBE3 plus temperature sensor 03P-4302 16/07//2010 -
Secondary temperature sensor Sea-Bird SBE3 plus temperature sensor 03P-4235 25/06/2010 -
Underwater PAR sensor Biospherical instruments QCD905L underwater PAR sensor 7274 12/1/2009 -
Dissolved oxygen sensor Sea-Bird SBE43 dissolved oxygen sensor 0676 09/07/2010 -
Altimeter Benthos altimeter 2130.27001 - -
Underwater fluorometer Chelsea Aquatracka MkIII (#AQU3598, 6000m) underwater fluorometer 088-216 27/08/2009 -
Underwater transmissometer Wet Labs C-Star 6000 m underwater transmissometer, pathlength 25 cm, wavelength 660 nm. CST-396DR 23/08/2007 -
Primary submersible pump Sea-Bird 5T submersible pump 05T-2371 - -
Secondary submersible pump Sea-Bird 5T submersible pump 05T-2395 - -
LADCP (Lowered Acoustic Doppler Profiler) TRDI WorkHorse 300 kHz LADCP 12736 - Downward-looking master
LADCP (Lowered Acoustic Doppler Profiler) TRDI WorkHorse 300 kHz LADCP 1855 (casts 1-45) 12369 (casts 46-54) - Upward-looking slave
LADCP battery pack NOC WorkHorse WH005 - -

Sea-Bird Electronics SBE 911 and SBE 917 series CTD profilers

The SBE 911 and SBE 917 series of conductivity-temperature-depth (CTD) units are used to collect hydrographic profiles, including temperature, conductivity and pressure as standard. Each profiler consists of an underwater unit and deck unit or SEARAM. Auxiliary sensors, such as fluorometers, dissolved oxygen sensors and transmissometers, and carousel water samplers are commonly added to the underwater unit.

Underwater unit

The CTD underwater unit (SBE 9 or SBE 9 plus ) comprises a protective cage (usually with a carousel water sampler), including a main pressure housing containing power supplies, acquisition electronics, telemetry circuitry, and a suite of modular sensors. The original SBE 9 incorporated Sea-Bird's standard modular SBE 3 temperature sensor and SBE 4 conductivity sensor, and a Paroscientific Digiquartz pressure sensor. The conductivity cell was connected to a pump-fed plastic tubing circuit that could include auxiliary sensors. Each SBE 9 unit was custom built to individual specification. The SBE 9 was replaced in 1997 by an off-the-shelf version, termed the SBE 9 plus , that incorporated the SBE 3 plus (or SBE 3P) temperature sensor, SBE 4C conductivity sensor and a Paroscientific Digiquartz pressure sensor. Sensors could be connected to a pump-fed plastic tubing circuit or stand-alone.

Temperature, conductivity and pressure sensors

The conductivity, temperature, and pressure sensors supplied with Sea-Bird CTD systems have outputs in the form of variable frequencies, which are measured using high-speed parallel counters. The resulting count totals are converted to numeric representations of the original frequencies, which bear a direct relationship to temperature, conductivity or pressure. Sampling frequencies for these sensors are typically set at 24 Hz.

The temperature sensing element is a glass-coated thermistor bead, pressure-protected inside a stainless steel tube, while the conductivity sensing element is a cylindrical, flow-through, borosilicate glass cell with three internal platinum electrodes. Thermistor resistance or conductivity cell resistance, respectively, is the controlling element in an optimized Wien Bridge oscillator circuit, which produces a frequency output that can be converted to a temperature or conductivity reading. These sensors are available with depth ratings of 6800 m (aluminium housing) or 10500 m (titanium housing). The Paroscientific Digiquartz pressure sensor comprises a quartz crystal resonator that responds to pressure-induced stress, and temperature is measured for thermal compensation of the calculated pressure.

Additional sensors

Optional sensors for dissolved oxygen, pH, light transmission, fluorescence and others do not require the very high levels of resolution needed in the primary CTD channels, nor do these sensors generally offer variable frequency outputs. Accordingly, signals from the auxiliary sensors are acquired using a conventional voltage-input multiplexed A/D converter (optional). Some Sea-Bird CTDs use a strain gauge pressure sensor (Senso-Metrics) in which case their pressure output data is in the same form as that from the auxiliary sensors as described above.

Deck unit or SEARAM

Each underwater unit is connected to a power supply and data logging system: the SBE 11 (or SBE 11 plus ) deck unit allows real-time interfacing between the deck and the underwater unit via a conductive wire, while the submersible SBE 17 (or SBE 17 plus ) SEARAM plugs directly into the underwater unit and data are downloaded on recovery of the CTD. The combination of SBE 9 and SBE 17 or SBE 11 are termed SBE 917 or SBE 911, respectively, while the combinations of SBE 9 plus and SBE 17 plus or SBE 11 plus are termed SBE 917 plus or SBE 911 plus .

Specifications

Specifications for the SBE 9 plus underwater unit are listed below:

Parameter Range Initial accuracy Resolution at 24 Hz Response time
Temperature -5 to 35°C 0.001°C 0.0002°C 0.065 sec
Conductivity 0 to 7 S m -1 0.0003 S m -1 0.00004 S m -1 0.065 sec (pumped)
Pressure 0 to full scale (1400, 2000, 4200, 6800 or 10500 m) 0.015% of full scale 0.001% of full scale 0.015 sec

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

BODC Processing

Fifty three profiles were provided by the originator with CTD002 and CTD016 being omitted, as these were aborted. Data from the auxiliary sensors were also not provided. The data were received in a structured matlab format and converted into BODC internal format (QXF). The following table shows how the variables within the matlab file were mapped to appropriate BODC parameter codes:

Originator's Parameter Name Units Description BODC Parameter Code Units Comments
temperature °C Temperature from primary sensor TEMPS901 °C -
salinity - Practical salinity PSALCC01 Dimensionless Calculated using conductivity from secondary sensor and calibrated against CTD bottle salinity samples
pressure dbar Pressure exerted by the water column PRESPR01 dbar -
- - Potential temperature POTMCV01 °C Generated by BODC using the Fofonoff and Millard (1983) algorithm
- - Sigma-theta SIGTPR01 kg m -3 Generated by BODC using the Fofonoff and Millard (1983) algorithm

The reformatted data were visualised using the in-house EDSERPLO software. No data values were edited or deleted. Quality control flags were applied to data as necessary. Overall no quality issues with very few flags added.

References

Fofonoff, N.P. and Millard, R.C., 1983 . Algorithms for computations of fundamental properties of seawater. UNESCO Technical Papers in Marine Science, No.44, 53pp.

Originator's Data Processing

Sampling Strategy

Fifty five CTD profiles were performed during the cruise. At stations where Vertical Microstructure Profilers (VMPs) were deployed, the CTD deployment duration had to approximately match the VMP cast duration, within 1.5 hours. There were several problems which occurred during the deployment of the CTDs. CTD002 was aborted at 1000 m and CTD016 at 1700 m due to termination problems related to shortage within the electric cable between the CTD and the ship, and 50 m of cable was chopped twice to solve the problem. CTD049 was aborted to catch the VMP, and during CTD050 the was a wire out offset variable throughout cast.

Data processing

The files were produced by Seasave and initial data processing was performed using Sea-Bird processing software. Firstly, the raw data were converted into physical units using 'data conversion', the surface soak was removed from the data and the surface pressure offset obtained from the first 30 readings was applied. Temporal shifts were then applied to align the sensor readings using 'align CTD'. Corrections for the thermal mass of the cell were made using 'cell thermal mass' and the output from the align CTD, in order to minimise salinity spiking in steep vertical gradients due to temperature/conductivity mismatch.

After the Sea-Bird processing a further set of processing using Mstar programs were applied. The data were firstly averaged to 1 Hz, then the practical salinity and potential temperature were calculated. The downcast data was extracted, gaps were interpolated and the data were then averaged to 2 dbar. All profiles were visually checked to detect any possible anomalies, and profiles were also plotted on top of each other in order to detect any possible sensor drift. A number of small localised spikes were detected in the conductivity/salinity profiles and these were removed and replaced by null values.

An electric problem caused large spikes in the data (all sensors) from station 43 onwards, the problem was not solved at the time but the profiles were cleaned during post-processing.

Field Calibrations

Salinity

Between five and seven Niskin bottles were sampled for salinity at each station. Surface and bottom bottles were chosen as well as a couple of bottles at tracer cluster depths. The salinity differences between bottle salinities and salinities from sensor 1 showed a strong jump between stations 38 and 41. The reason for this sudden failure of sensor 1 was not known. In contrast, there was no failure or jump in salinities from sensor 2. The salinity differences between bottle salinities and salinities from sensor 2 all fell within ± 0.002. No clear trend or pattern in pressure or time dependence was identified. Density (θ) profiles were used to detect possible sensor drift, and all θ characteristics of bottom water sampled during the cruise were found to fall within the same narrow band. There was a change noted in the salinity from the beginning to end of the cruise, with fresher salinities at the beginning, however, this was thought to be a real change as it did not appear to be a constant shift and the difference was also consistent with previous bottom water studies. Based upon the analyses conducted, it was concluded that data from sensor 2 with no calibration should be used as if the calibration was applied it would be less than the targeted accuracy.


Project Information

Diapycnal and Isopycnal Mixing Experiment in the Southern Ocean (DIMES) project document

DIMES is a US/UK field program aimed at measuring diapycnal and isopycnal mixing in the Southern Ocean, along the tilting isopycnals of the Antarctic Circumpolar Current.

The Meridional Overturning Circulation (MOC) of the ocean is a critical regulator of the Earth's climate processes. Climate models are highly sensitive to the representation of mixing processes in the southern limb of the MOC, within the Southern Ocean, although the lack of extensive in situ observations of Southern Ocean mixing processes has made evaluation of mixing somewhat difficult. Theories and models of the Southern Ocean circulation have been built on the premise of adiabatic flow in the ocean interior, with diabatic processes confined to the upper-ocean mixed layer. Interior diapycnal mixing has often been assumed to be small, but a few recent studies have suggested that diapycnal mixing might be large in some locations, particularly over rough bathymetry. Depending on its extent, this interior diapycnal mixing could significantly affect the overall energetics and property balances for the Southern Ocean and in turn for the global ocean. The goals of DIMES are to obtain measurements that will help us quantify both along-isopycnal eddy-driven mixing and cross-isopycnal interior mixing.

DIMES includes tracer release, isopycnal following RAFOS floats, microstructure measurements, shearmeter floats, EM-APEX floats, a mooring array in Drake Passage, hydrographic observations, inverse modeling, and analysis of altimetry and numerical model output.

DIMES is sponsored by the National Science Foundation (U.S.), Natural Environment Research Council (U.K) and British Antarctic Survey (U.K.)

For more information please see the official project website at DIMES


Data Activity or Cruise Information

Cruise

Cruise Name JR20110409 (JR276, UKD-2.5)
Departure Date 2011-04-09
Arrival Date 2011-04-26
Principal Scientist(s)Andrew J Watson (University of East Anglia School of Environmental Sciences)
Ship RRS James Clark Ross

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:

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