Metadata Report for BODC Series Reference Number 1090174

• 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

Problem Report

Beam attenuance and transmissance: The majority of the transmissometer profiles are of poor quality at depth. The problem is evident on both SS and TT frame profiles although expressed slightly differently for the sensor on each rig. It appears to be a transmissometer problem related to environmental conditions such as for example where temperature or temperature gradients were beyond an acceptable threshold. The stainless steel rig mounted transmissometer displayed steps in the profile during solar noon casts only for casts 49 to 55. These steps appear when the rig was left hanging at a depth during the downcast and are likely due to the instrument cooling from the ambient on deck temperature as the profile is carried out. This effect is present on most casts for both sensors but is particularly obvious on the solar noon casts. The titanium rig mounted tranmissometer behaved suspiciously for casts 53 to 64, showing large but smooth attenuance maximum at depth as well as strong drifts. It is telling that the anomalies are not depth related but seem to be related to the depth of the thermocline i.e. these anomalies are consistently observed at the base of the strong thermocline. The anomalies observed during AMT20 are likely due to a severe case of hysteresis produced by air and water temperature in excess of the instruments operating range (1 to 25 °C). This has been observed on AMT cruises before and reported by Jeff Benson (e.g. AMT12).

The Chelsea transmissometers have been calibrated with pure water as the reference for 100% transmission and therefore beam attenuation values in clear water should be close to 0 m^-1. Chelsea Instruments advise that ALPHAtracka is calibrated at the factory at 20°C in distilled water with an electrical conductivity less than one µS cm^-1and filtered to better than 5 µm and that it is possible that the user will encounter water which is purer than that used during the calibration. Indeed the minimum attenuance values for the profiles from the stainless steel rig mounted tranmissometer were lower then 0 m^-1 for many casts, suggesting that the calibration procedure recommended by Sea-Bird and Chelsea Instruments may need adjusting to use deep clear oceanic water as the reference for 100% transmission. The attenuance data from the transmissometers will need further offset correction to bring them in line with recognised values. Whether this should be done for the dataset as a whole or on a cast by cast basis is for the user to decide based on their requirements. The absolute attenuation values are therefore questionable but the relative profile should be reliable except for profiles where hysteresis was a problem at depth.

James Cook Cruise JC053 AMT20 CTD Data Quality Document

Chlorophyll

The sample calibrations for the fluorometers were optimised for the euphotic zone. As a result many of the calibrated chlorophyll values for the profiles below 150 - 200 dbar were slightly less than zero. All negative values were flagged as suspect. Users should therefore use caution when integrating the values over the entire profile. As the data were binned to 1 dbar some bins may have been derived by interpolation and were flagged accordingly. Where chlorophyll data values were negative the flag indicating interpolation was overwritten. The original flagged interpolated data are available on request.

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

Sea-Bird Dissolved Oxygen Sensor SBE 43 and SBE 43F

The SBE 43 is a dissolved oxygen sensor designed for marine applications. It incorporates a high-performance Clark polarographic membrane with a pump that continuously plumbs water through it, preventing algal growth and the development of anoxic conditions when the sensor is taking measurements.

Two configurations are available: SBE 43 produces a voltage output and can be incorporated with any Sea-Bird CTD that accepts input from a 0-5 volt auxiliary sensor, while the SBE 43F produces a frequency output and can be integrated with an SBE 52-MP (Moored Profiler CTD) or used for OEM applications. The specifications below are common to both.

Specifications

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

James Cook Cruise JC053 AMT20 CTD Instrumentation

Two different CTD frames were used - a stainless steel frame and a titanium frame used for trace metal sampling.

Stainless Steel

The CTD unit was a Sea-Bird Electronics 911plus system, with dissolved oxygen sensor. The CTD was fitted with a transmissometer and a fluorometer. All instruments were attached to a stainless steel frame equipped with a Sea-Bird SBE 32 carousel. The table below lists more detailed information about the various sensors.

Change of sensors during cruise: The secondary conductivity, upwelling PAR, Wetlabs Backscatter and fluorometer sensors were changed during the cruise.

Sampling device

Rosette sampling system equipped with 24 x 20 l sampling bottles (manufactured by Ocean Test Equipment Inc.).

Titanium

The CTD unit was a Sea-Bird Electronics 911plus system, with dissolved oxygen sensor. The CTD was fitted with a transmissometer and a fluorometer. All instruments were attached to a titanium frame equipped with a Sea-Bird SBE 32 carousel (titanium). The table below lists more detailed information about the various sensors.

Change of sensors during cruise: No instrument changes were made to the titanium rig during the cruise.

Sampling device

Rosette sampling system equipped with 24 x 10 l trace metal free sampling bottles (manufactured by Ocean Test Equipment Inc.).

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:

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

Chelsea Technologies Group Aquatracka MKIII fluorometer

The Chelsea Technologies Group Aquatracka MKIII is a logarithmic response fluorometer. Filters are available to enable the instrument to measure chlorophyll, rhodamine, fluorescein and turbidity.

It uses a pulsed (5.5 Hz) xenon light source discharging along two signal paths to eliminate variations in the flashlamp intensity. The reference path measures the intensity of the light source whilst the signal path measures the intensity of the light emitted from the specimen under test. The reference signal and the emitted light signals are then applied to a ratiometric circuit. In this circuit, the ratio of returned signal to reference signal is computed and scaled logarithmically to achieve a wide dynamic range. The logarithmic conversion accuracy is maintained at better than one percent of the reading over the full output range of the instrument.

Two variants of the instrument are available, both manufactured in titanium, capable of operating in depths from shallow water down to 2000 m and 6000 m respectively. The optical characteristics of the instrument in its different detection modes are visible below:

* The wavelengths for the turbidity filters are customer selectable but must be in the range 400 to 700 nm. The same wavelength is used in the excitation path and the emission path.

The instrument measures chlorophyll a, rhodamine and fluorescein with a concentration range of 0.01 µg l^-1 to 100 µg l^-1. The concentration range for turbidity is 0.01 to 100 FTU (other wavelengths are available on request).

The instrument accuracy is ± 0.02 µg l^-1 (or ± 3% of the reading, whichever is greater) for chlorophyll a, rhodamine and fluorescein. The accuracy for turbidity, over a 0 - 10 FTU range, is ± 0.02 FTU (or ± 3% of the reading, whichever is greater).

Further details are available from the Aquatracka MKIII specification sheet.

Chelsea Technologies Group ALPHAtracka and ALPHAtracka II transmissometers

The Chelsea Technologies Group ALPHAtracka (the Mark I) and its successor, the ALPHAtracka II (the Mark II), are both accurate (< 0.3 % fullscale) transmissometers that measure the beam attenuation coefficient at 660 nm. Green (565 nm), yellow (590 nm) and blue (470 nm) wavelength variants are available on special order.

The instrument consists of a Transmitter/Reference Assembly and a Detector Assembly aligned and spaced apart by an open support frame. The housing and frame are both manufactured in titanium and are pressure rated to 6000 m depth.

The Transmitter/Reference housing is sealed by an end cap. Inside the housing an LED light source emits a collimated beam through a sealed window. The Detector housing is also sealed by an end cap. A signal photodiode is placed behind a sealed window to receive the collimated beam from the Transmitter.

The primary difference between the ALPHAtracka and ALPHAtracka II is that the Alphatracka II is implemented with surface-mount technology; this has enabled a much smaller diameter pressure housing to be used while retaining exactly the same optical train as in the Mark I. Data from the Mark II version are thus fully compatible with that already obtained with the Mark I. The performance of the Mark II is further enhanced by two electronic developments from Chelsea Technologies Group - firstly, all items are locked in a signal nulling loop of near infinite gain and, secondly, the signal output linearity is inherently defined by digital circuitry only.

Among other advantages noted above, these features ensure that the optical intensity of the Mark II, indicated by the output voltage, is accurately represented by a straight line interpolation between a reading near full-scale under known conditions and a zero reading when blanked off.

For optimum measurements in a wide range of environmental conditions, the Mark I and Mark II are available in 5 cm, 10 cm and 25 cm path length versions. Output is default factory set to 2.5 volts but can be adjusted to 5 volts on request.

Further details about the Mark II instrument are available from the Chelsea Technologies Group ALPHAtrackaII specification sheet.

Chelsea Technologies Photosynthetically Active Radiation (PAR) Irradiance Sensor

This sensor was originally designed to assist the study of marine photosynthesis. With the use of logarithmic amplication, the sensor covers a range of 6 orders of magnitude, which avoids setting up the sensor range for the expected signal level for different ambient conditions.

The sensor consists of a hollow PTFE 2-pi collector supported by a clear acetal dome diverting light to a filter and photodiode from which a cosine response is obtained. The sensor can be used in moorings, profiling or deployed in towed vehicles and can measure both upwelling and downwelling light.

Specifications

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

Paroscientific Absolute Pressure Transducers Series 3000 and 4000

Paroscientific Series 3000 and 4000 pressure transducers use a Digiquartz pressure sensor to provide high accuracy and precision data. The sensor comprises a quartz crystal resonator that responds to pressure-induced stress, and temperature is measured for thermal compensation of the calculated pressure.

The 3000 series of transducers includes one model, the 31K-101, whereas the 4000 series includes several models, listed in the table below. All transducers exhibit repeatability of better than ±0.01% full pressure scale, hysteresis of better than ±0.02% full scale and acceleration sensitivity of ±0.008% full scale /g (three axis average). Pressure resolution is better than 0.0001% and accuracy is typically 0.01% over a broad range of temperatures.

Differences between the models lie in their pressure and operating temperature ranges, as detailed below:

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

James Cook Cruise JC053 AMT20 CTD Processing

Sampling strategy

A total of 89 successful CTD casts were made during the cruise.

All 89 casts were conventional profiling casts with water sampling. Both a stainless steel (SS) and a titanium (TT) CTD system were used. The SS frame was normally deployed daily at ~05:30 and ~13:00 (ship time). The TT frame was normally deployed daily at ~04:30 (ship time); however from 9^th November only the SS frame was used with deployments at ~04:30 and ~13:00 ship time each day. A total of 22 titanium and 67 stainless steel profiles were completed.

Due to a termination failure at 500m on both casts 59 and 60, no bottles could be fired and no data was acquired from the up casts.

Cruise data processing

CTD casts were recorded using the SeaBird data collection software Seasave-Win32. Data were reprocessed at BODC because of concerns about LoopEdit under certain conditions using SBE Data Processing-Win32 v7.20g and the oxygen hysteresis module was used in the calculation of the oxygen channel; the processing routines are named after each stage in brackets. The software applied the calibrations as appropriate through the instrument configuration file to the data in engineering units output by the CTD hardware. The Altimeter data streams were not transferred during processing.

An ascii file including the 24 Hz data for up and down casts was generated along with a bottle file containing all the information from the instant the bottle was fired for each cast (DatCnv). Pressure spikes were removed (WildEdit), the oxygen sensor was then shifted relative to the pressure by 2 seconds, to compensate for the lag in the sensor response time (AlignCTD) and the effect of thermal 'inertia' on the conductivity cells was removed (CellTM). The CTD files produced from SeaBird processing were converted from 24 Hz ascii files into a 2 Hz file (BinAverage). A file was created for each cast containing the mean values of all the variables at the bottle firing locations (Bottle Summary).

During the cruise water samples were collected from rosette bottle on each cast and bench salinometer, Winkler titration and fluorometric analyses made to determine accurate salinity, dissolved oxygen concentration and extracted chlorophyll-a measurements. These data were compared with values from the CTD sensors at bottle firing and a sample calibration derived for the salinity, oxygen and fluorometer channels.

The BBRTD channels have been dropped in the banked files as there are no data for these instruments in the dataset, but these channels are available on request. The calibrated BBRTD profiles will be available separately once they are provided by the scientist responsible for the instrument but the post-cruise calibration has yet to be fully derived and applied.

BODC post-processing and screening

• Reformatting

  The data were converted from SeaBird ascii format into BODC internal format (QXF) using BODC transfer function 357. The following table shows how the SeaBird variables were mapped to appropriate BODC parameter codes:

  Originator's Parameter Name	Units	Description	BODC Parameter Code	Units	Comments
  Pressure, Digiquartz	dbar	CTD pressure	PRESPR01	dbar	-
  Temperature [ITS-90]	°C	Temperature of water column by CTD	TEMPCU01	°C	-
  Temperature, 2 [ITS-90]	°C	Temperature of water column by CTD	TEMPCU02	°C	-
  Salinity	-	Practical salinity of the water body by CTD	PSALCU01	-	-
  Salinity, 2	-	Practical salinity of the water body by CTD	PSALCU02	-	-
  oxygen	ml l-1	Dissolved oxygen concentration	DOXYSU01	µmol l-1	Converted from ml l-1 to µmol l-1 by multiplying the original value by 44.66.
  fluor	mg m-3	Fluorometer nominal chlorophyll-a	CPHLPM01	mg m-3	-
  PAR irradiance	W m-2	Downwelling PAR irradiance	DWIRPP01	W m-2	-
  PAR irradiance	W m-2	Upwelling PAR irradiance	UWIRPP01	W m-2	-
  Voltage 6	V	BBRTD (red LED) voltage	NVLTWR01	V	-
  Voltage 6	V	BBRTD (green LED) voltage	NVLTWG01	V	-
  Trans	m-1	Transmissance	POPTDR01	%	25cm pathlength
  Atten	m-1	Beam attenuance	ATTNDR01	m-1	25cm pathlength
  Trans	m-1	Transmissance	POPTSR01	%	10cm pathlength
  Atten	m-1	Beam attenuance	ATTNSR01	m-1	10cm pathlength
  -	-	Practical salinity of the water body by CTD	PSALCC01	-	BODC calibration of PSALCU01 against bench salinometer samples
  -	-	Practical salinity of the water body by CTD	PSALCC02	-	BODC calibration of PSALCU02 against bench salinometer samples
  -	-	Oxygen	DOXYSC01	µmol l-1	BODC calibration of DOXYSU01 against Winkler samples
  -	-	Chlorophyll-a	CPHLPS01	mg m-3	BODC calibration of CPHLPM01 against HPLC pigment samples
  -	-	Oxygen saturation	OXYSSC01	%	Generated by BODC using the Benson and Krause (1984) algorithm with parameters DOXYSC01, PSALCC01 and TEMPCU01
  -	-	Potential temperature	POTMCV01	°C	Generated by BODC using UNESCO Report 38 (1981) algorithm with parameters PSALCC01 and TEMPCU01
  -	-	Sigma-theta	SIGTPR01	kg m-3	Generated by BODC using the Fofonoff and Millard (1982) algorithm

• References

  Benson, B.B. and Krause, D., 1984. The concentration and isotopic fractionation of oxygen dissolved in freshwater and seawater in equilibrium with the atmosphere. Limnol. Oceanogr., 29(3), 620-632

  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.

  UNESCO, 1981. Background papers and supporting data on the International Equation of State of Seawater 1980. UNESCO Technical Papers in Marine Science No. 38, 192pp

• Screening

  Reformatted CTD data were transferred onto a graphics work station for visualisation using the in-house editor EDSERPLO. Downcasts and upcasts were differentiated and the limits manually flagged. No data values were edited or deleted. Flagging was achieved by modification of the associated BODC quality control flag for suspect or null values.

  From visual screening of the 2Hz data profiles, it was clear that on occasions during the cruise salinity and temperature profiles suffered from the problem of ship's heave/entrainment, which has now become conspicuous on most cruises. The effect was greater in the profiles from the stainless steel rig with the 20 l niskin bottles. The primary temperature and conductivity sensors were located within the frame and the secondary temperature and conductivity sensors were deployed on an external fin. The entrainment features were greatly reduced in the data from the secondary sensors. However the data from the primary sensor channels were considered more reliable due to problems with the secondary conductivity channel during the cruise and entrainment anomalies were flagged systematically whenever it was believed that they would affect the quality of the 1 dbar-binned data.

• Screening notes regarding specific casts:

  Temperature and salinity: Salinity profiles from the vane mounted sensor on the stainless steel rig showed great variability for casts 27-37 and have been flagged suspect. The problem was resolved by changing the sensor (cast 30s) and then the pump (cast 39s). All salinity data from the secondary sensor have been flagged suspect for the stainless steel casts from 27 and 29. Casts where severe entrainment features were visible; 32t (100-220 db), 36s, 37s (all cast), 40s (60-140 db), 49s (50-200 db), 50t (35-120 db), 52s (30-300 db), 55s (50-200 db), 56t (85-135 db), 74s (60-300 db), 76s (all cast), 77s (30-180 db), 79s (30-100 db), 81s (30-190 db), 87s (50-120 db), 88s (160-260db) and 89s (60-80 db). Cast 60s has had the salinity data flagged between 50-80 db.

  Dissolved oxygen: The channel shows variation for the majority of casts, whether this reflects natural variability or entrainment is not always clear. For some casts where the variation is minimal the entrainment problem where obvious has been flagged, however the variability on most casts makes it difficult to distinguish.

  Fluorescence: No obvious problem with entrainment for the fluorometer channels. Some small observations follow but limited additional flagging has taken place at this stage. Casts 57, 77 and 88 had some spiking flagged.

  Cruise documentation indicates a problem with the TT rig fluorometer during the up-cast of CTD041t. The problem only appeared during the up-cast and manifested as a drop to 0 volts before returning a diminished signal for the rest of the up-cast. The cable was changed prior to cast CTD059t but the problem persisted. The fluorometer was changed after CTD64t and instrument S/N 09-7117-001 replaced instrument S/N 088224. A change to the science programme resulted in the titanium rig not being used from this point in the cruise.

  Beam attenuance and transmissance: The majority of the transmissometer profiles are of poor quality. The problem is evident on both SS and TT frame profiles which suggests a transmissometer problem related to environmental conditions such as for example where temperature or temperature gradients were beyond an acceptable threshold. It is telling that the anomalies are not depth or sensor related but seems to be related to the depth of the thermocline i.e. anomalies are consistently observed at the base of the strong thermocline. From cast 19s onwards the transmissometers start behaving suspiciously, showing large but smooth attenuance maximum at depth as well as strong drifts (e.g. cast 64t).The anomalies disappear much later in the cruise from cast 78s. The transmissometer data are calibrated from manufacturer's calibration coefficients and the attenuance and transmission values should not be used as absolute values but for the relative profile trend where data values have not been flagged. The anomalies observed during AMT20 are likely due to a severe case of hysteresis produced by air and water temperature in excess of the instruments operating range (1 to 25 °C). This has been observed on AMT cruises before and reported by Jeff Benson (e.g. AMT12-17).

  Downwelling and upwelling PAR: For the down- and up-welling PAR profiles, spiky data were generally associated with movement when the package was going down too slowly and "bouncing" in the surface layer. However the majority of casts were not flagged given that the variation can be the result of variation in surface conditions (e.g. changing cloud cover).

• Banking

  Once quality control screening was complete, the CTD downcasts were banked. Finally, the data were binned against pressure at 1 dbar increments with flagged data excluded from the bin averaging. The primary salinity, temperature, density and potential temperature channels were retained as the best quality data channels from the two sensors.

Field Calibrations

• Pressure

  There were no casts where the CTD pressure was logging in air. No adjustments were made to the values resulting from application of manufacturer's coefficients during the initial processing.

• Temperature

  Temperature readings from the two temperature sensors were almost identical outside of entrainment features and no other independent measurements of better quality were available. No further correction was therefore applied to the data.

• Salinity

  The salinity data were calibrated using the sensor readings from the up-cast at the point when the bottles were fired and the discrete salinity data measured using the bench salinometer on water samples collected from bottles. The samples collected were from the deepest depth for each cast. Offsets were generated between the salinometer and CTD sensor values and plotted against cast and salinometer values. The calibration set for the secondary sensor on the stainless steel rig was subdivided between the casts where the sensor was changed.

  The linear regressions of offset against bench salinometer data for the stainless steel cast were not significant and so offsets were generated. All sensors appeared to show a drift with time, however with only one sample collected from the deepest sampled depth on each cast this could not be investigated further as it was not possible to determine if the offset was fixed or varied with salinity for each cast. Three offsets were applied to primary sensor (casts 1-59, 60-69 and 70-89) and two to the secondary sensor (casts 1-29 and 30-89).

  Casts	Calibration	N	R2	BODC cal ref
  1 - 59	PSALCC01 = PSALCU01 + 0.0028 (± 0.0013)	27	-	6576
  60 - 69	PSALCC01 = PSALCU01 + 0.0049 (± 0.0015)	3	-	6577
  70 - 89	PSALCC01 = PSALCU01 + 0.0072 (± 0.0015)	17	-	6578
  1 - 29	PSALCC02 = PSALCU02 + 0.0049 (± 0.0022)	15	-	6579
  30 - 89	PSALCC02 = PSALCU02 + 0.0038 (± 0.0028)	27	-	6580

  There were no problems with the conductivity sensors deployed on the titanium rig. The primary sensor had a small offset of +0.0001, which was consistent over time and with the secondary sensor the offset had a significant linear regression with the bench salinometer measurements and a subsequent offset of +0.0016 once the trend was corrected.

  Casts	Calibration	N	R2	BODC cal ref
  All	PSALCC01 = PSALCU01 + 0.0001 (± 0.0010)	19	-	6557
  All	PSALCC02 = 0.9979 * PSALCU02 + 0.0761	20	0.640	6558

  The reduction in the RMS residual indicates an improved match to the bench salinometer sample dataset after calibration (stainless steel rig sensor 1: uncalibrated RMS = 0.553, calibrated RMS = 0.033; stainless steel rig sensor 2: uncalibrated RMS = 0.553, calibrated RMS = 0.033; titanium rig sensor 1: uncalibrated RMS = 0.158, calibrated RMS = 0.039; titanium rig sensor 2: uncalibrated RMS = 0.158, calibrated RMS = 0.039).

• Dissolved oxygen

  The oxygen sensors were calibrated using the sensor readings from the up-cast at the point when the bottles were fired and the dissolved oxygen concentrations from Winkler titrations on water samples collected from the bottles. The samples collected were from a range of depths on a number of casts throughout the cruise.

  The oxygen sensors on both rigs operated without problem during the cruise. 206 samples were taken from the stainless steel rig casts during the cruise. The oxygen calibration was split because there were two subgroups which were apparent in the calibration dataset. This was highlighted by the scientist carrying out the Winkler titrations onboard the cruise. After comparison between the surface Winkler titration oxygen saturation values and the surface calibrated sensor saturation values, the sensor values showed a drift below 100% saturation not reflected in the Winkler titration data. Therefore it was decided to split the calibration dataset. The calibration was carried out for two sections which split the cruise before and after Ascension Island (casts 1-67 and 68-89). The linear regression of offset against Winkler oxygen concentration was significant for both calibrations (n=97; R²=0.84; p<0.001 and n=88; R²=0.84; p<0.001).

  Casts	Calibration	N	R2	BODC cal ref
  1 - 66	DOXYSC01 = 1.1064 * DOXYSU01 + 5.7468	97	0.840	6566
  67 - 89	DOXYSC01 = 1.0800 * DOXYSU01 + 7.5969	97	0.840	6567

  121 samples were taken from the titanium rig casts during the cruise. An analysis of the calibration dataset in its entirety had a non significant regression of the offset against Winkler oxygen concentration (n=108; R²<0.001; p=0.99). However when the offset was plotted against cast number a step in the offsets became apparent. Therefore the calibration was split into 2 groups (casts 2-17 and cast 20-64) with an offset applied for the first group of casts and a regression against Winkler concentrations for the second group.

  Casts	Calibration	N	R2	BODC cal ref
  2 - 17	DOXYSC01 = DOXYSU01 + 3.0330	25	-	6564
  20 - 64	DOXYSC01 = 1.0361 * DOXYSU01 + 0.5969	83	0.380	6565

  The reduction in the RMS residual indicates an improved match to the Winkler titration dataset after calibration (stainless steel rig sensor: uncalibrated RMS = 0.553, calibrated RMS = 0.033; titanium rig sensor: uncalibrated RMS = 0.158, calibrated RMS = 0.039).

• Fluorescence

  The CTD deployed fluorometers were calibrated against extracted chlorophyll-a measurements made on seawater collected by Niskin bottles from up to 6 depths at each station. When both CTD rigs were being deployed each CTD was sampled once per day. After Ascension Island when the stainless steel rig was used for all casts, a reduced number of samples were taken from the noon cast.

  The stainless steel rig fluorometer operated without problems until cast 86 when the voltage dropped out during the up-cast. The cable was tightened before cast 87 and then changed before cast 88; while the down-cast on all three casts appeared to be OK the drop outs on the up-cast persisted for both casts 87 and 88. This resulted in the bottle firing data for these casts being unreliable for use in the calibration. Cast 86 was not calibrated, while casts 87 and 88 were calibrated taking the nominal chl-a values from the down-cast at the relevant bottle firing depths. The fluorometer was then replaced for the final cast 89. The calibration was split between four regions along the cruise track for the fluorometer in use from casts 1 to 85. There were further separate calibrations for each of the suspect casts and for the final cast with the new fluorometer.

  Casts	Calibration	N	R2	BODC cal ref
  4 - 7	CPHLPS01 = 1.4544 (± 0.0327) * CPHLPM01	9	0.79	6568
  9 - 13	CPHLPS01 = 2.0345 (± 0.0098) * CPHLPM01	10	0.89	6569
  15 - 79	CPHLPS01 = 3.0583 (± 0.0098) * CPHLPM01	110	0.97	6570
  80 - 85	CPHLPS01 = 2.0718 (± 0.0120) * CPHLPM01	22	0.94	6571
  87	CPHLPS01 = 2.0386 (± 0.0200) * CPHLPM01	9	0.79	6573
  88	CPHLPS01 = 1.4179 (± 0.0078) * CPHLPM01	3	0.50	6574
  89	CPHLPS01 = 1.9910 (± 0.0219) * CPHLPM01	4	0.66	6575

  The problem during up-cast observed on the titanium rig fluorometer produced unreliable data to calibrate the sensor from the bottle files. The titanium rig was therefore calibrated against sensor values taken from the down-cast at the same depth as the bottles were fired. The calibration was split between five regions along the cruise track.

  Casts	Calibration	N	R2	BODC cal ref
  2 - 11	CPHLPS01 = 1.7130 (± 0.0183) * CPHLPM01	15	0.90	6559
  14 - 28	CPHLPS01 = 5.3169 (± 0.0166) * CPHLPM01 - 0.0606 (± 0.0038)	159	0.907	6560
  32 - 41	CPHLPS01 = 4.4718 (± 0.0218) * CPHLPM01 - 0.0957 (± 0.0045)	24	0.98	6561
  44 - 53	CPHLPS01 = 6.4238 (± 0.0302) * CPHLPM01 - 0.1933 (± 0.0106)	18	0.98	6562
  56 - 64	CPHLPS01 = 3.8976 (± 0.0111) * CPHLPM01 - 0.0791 (± 0.0042)	9	1.00	6563

  The reduction in the RMS residual indicates an improved match to the extracted chl-a sample dataset after calibration (stainless steel rig sensor: uncalibrated RMS = 0.224, calibrated RMS = 0.090; titanium rig sensor: uncalibrated RMS = 0.175, calibrated RMS = 0.078).

Project Information

Oceans 2025 Theme 10, Sustained Observation Activity 1: The Atlantic Meridional Transect (AMT)

The Atlantic Meridional Transect has been operational since 1995 and through the Oceans 2025 programme secures funding for a further five cruises during the period 2007-2012. The AMT programme began in 1995 utilising the passage of the RRS James Clark Ross between the UK and the Falkland Islands southwards in September and northwards in April each year. Prior to Oceans 2025 the AMT programme has completed 18 cruises following this transect in the Atlantic Ocean. This sustained observing system aims to provide basin-scale understanding of the distribution of planktonic communities, their nutrient turnover and biogenic export in the context of hydrographic and biogeochemical provinces of the North and South Atlantic Oceans.

The Atlantic Meridional Transect Programme is an open ocean in situ observing system that will:

• give early warning of any fundamental change in Atlantic ecosystem functionng
• improve forecasts of the future ocean state and associated socio-economic impacts
• provide a "contextual" logistical and scientific infrastructure for independently-funded national and international open ocean biogeochemical and ecological research.

The specific objectives are:

• To collect hydrographic, chemical, ecological and optical data on transects between the UK and the Falkland Islands
• To quantify the nature and causes of ecological and biogeochemical variability in planktonic ecosystems
• To assess the effects of variability in planktonic ecosystems on biogenic export and on air-sea exchange of radiatively active gases

The measurements taken and experiments carried out on the AMT cruises will be closely linked to Themes 2 and 5. The planned cruise track also allows for the AMT data to be used in providing spatial context to the Sustained Observation Activities at the Porcupine Abyssal Plain Ocean Observatory (SO2) and the Western Channel Observatory (SO10).

More detailed information on this Work Package is available at pages 6 - 9 of the official Oceans 2025 Theme 10 document: Oceans 2025 Theme 10

Weblink: http://www.oceans2025.org/

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: