Metadata Report for BODC Series Reference Number 1762248

• 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

Attenuance and transmittance

There whole of the transmittance and attenuance channels have been flagged. This is due to highly noisy data in both channels. Users should use caution when interpreting the transmissometer data.

AMT RRS Discovery Cruise D371 AMT21 Surface Hydrography Data Quality Document

The underway log sheets were used as a guide to the times when the non-toxic flow was switched off, dropped low or was adjusted during the cruise. Where there was noise in the channel at these times the data were flagged suspect. If there was no noise or spiking the data remain unflagged.

The sample calibrations applied to the TSG salinity, hull sensor temperature and fluorometer channels appear reasonable and did not produce suspect data in the calibrated channels. The calibrated fluorometer data exhibit large amounts of variability towards the end of the cruise in the southern Atlantic Ocean. The calibration in this area is not as closely matched to the sample data for this reason and users should keep this in mind when using the sample calibrated fluorometer data.

Attenuance and transmittance

There are some periods of noise within the transmissometer data, which may be the result of bubbles accumulating at the lens. There are other periods when there are steps in the data. Users should therefore apply caution when interpreting the transmissometer 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

SeaBird Digital Oceanographic Thermometer SBE38

The SBE38 is an ultra-stable thermistor that can be integrated as a remote temperature sensor with an SBE21 Thermosalinograph or an SBE 45 Micro TSG, or as a secondary temperature sensor with an SBE 16 plus, 16plus-IM, 16plus V2, 16plus-IM V2 or 19plus V2 SEACAT CTD.

Temperature is determined by applying an AC excitation to reference resistances and an ultra-stable aged thermistor. The reference resistor is a hermetically sealed VISHAY. AC excitation and ratiometric comparison using a common processing channel removes measurement errors due to parasitic thermocouples, offset voltages, leakage currents and gain errors.

The SBE38 can operate in polled sampling, where it takes one sample and transmits the data, or in continuous sampling.

Specifications

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

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.

WETLabs C-Star transmissometer

This instrument is designed to measure beam transmittance by submersion or with an optional flow tube for pumped applications. It can be used in profiles, moorings or as part of an underway system.

Two models are available, a 25 cm pathlength, which can be built in aluminum or co-polymer, and a 10 cm pathlength with a plastic housing. Both have an analog output, but a digital model is also available.

This instrument has been updated to provide a high resolution RS232 data output, while maintaining the same design and characteristics.

Specifications

Further details are available in the manufacturer's specification sheet or user guide.

AMT RRS Discovery Cruise D371 AMT21 Surface Hydrography Instrument Description Document

SeaBird MicroTSG Thermosalinograph SBE 45

The SBE45 MicroTSG is an externally powered instrument designed for shipboard measurement of temperature and conductivity of pumped near-surface water samples. The instrument can also compute salinity and sound velocity internally.

The MicroTSG comprises a platinum-electrode glass conductivity cell and a stable, pressure-protected thermistor temperature sensor. It also contains an RS-232 port for appending the output of a remote temperature sensor, allowing for direct measurement of sea surface temperature.

The instrument can operate in Polled, Autonomous and Serial Line Sync sampling modes:

• Polled sampling: the instrument takes one sample on command
• Autonomous sampling: the instrument samples at preprogrammed intervals and does not enter quiescence (sleep) state between samples
• Serial Line Sync: a pulse on the serial line causes the instrument to wake up, sample and re-enter quiescent state automatically

Specifications

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

AMT RRS Discovery Cruise D371 AMT21 Surface Hydrography Processing Procedures Document

Originator's Data Processing

During the cruise there was a dual logging system in place on the RRS Discovery. Data from the various instruments are logged to the RVS Level-C system and also as NetCDF (binary) through the Ifremer Techsas data logging system. The following instruments were logged during the cruise:
1) Wetlabs C-star 25 cm pathlength transmissometer (logged to RVS format in surfmet)
2) Wetlabs WetStar fluorometer (logged to RVS format in surfmet)
3) Seabird SBE38 Temperature sensor (logged to RVS format in seabird)
4) Seabird SBE45 MicroTSG (logged to RVS format in seabird)

BODC Data Processing

The last ~20 days TECHSAS files (except for the TSG data) were not saved to the post-cruise archive. TECHSAS files from 23 Oct 2011 to 13 Nov 2011 were missing. The RVS level-C files were confirmed complete by the originator. Since the TECHSAS file record for the cruise was incomplete the RVS Level-C files were chosen for transfer to the BODC underway file.

The surfmetX/surfmet and seabirdX/seabird data were transferred. A description of the channels present in the files, units, whether they were transferred, BODC parameter code and units, and if a unit conversion was applied during the transfer are detailed in the table below:

* temp_h, cond, temp_m not loaded from surfmet as where present these data are identical to the seabird file data but maybe delayed in time in the surfmet file (details on page 5 of the D371 Computing and Ship Systems Report)

Calibrations

Transmissometer - conversion from voltage using manufacturer's calibrations

The manufacturer's calibrations from the sheets supplied by NMF-SS have been applied through the BODC Calibration database.

BODC ICALRF 6723 POPTDR01 = 100 * (TVLTDR01 -0.059) / (4.661 - 0.059) = 21.7297 * TVLTDR01 - 1.2821

BODC ICALRF 6724 ATTNDR01 = -(1/0.25) * ln (POPTDR01 * 0.01)

Temperature

The hull temperature sensor data were calibrated against the CTD temperature sensors during the cruise. The data from the hull sensor at the CTD start time were compared with the temperature from the CTD at 7 decibars. The temperature offsets (CTD - Hull) were plotted against date/time and CTD sensor temperature and outliers identified. The relationships in the offset between sensors were then compared to the date/time and the CTD sensor temperature in separate linear regressions. There was no significant relationship with CTD sensor temperature (R²=-0.01; n = 60; F = 0.376; p = 0.542). There was a significant regression of offset with date/time (R² = 0.08; n = 60; F = 5.82; p = 0.019).

Applying the significant regression equation the offset was generated at the date/time when the non-toxic underway system was switched on (30/09/2011 08:00 offset = 0.0036) and when switched off at the end of the cruise (09/11/2011 14:00 offset = -0.0077). The offset was applied for the period in between by linear interpolation of these offsets through the BODC BUDS calibration routine (BODC ICALRF 6726).

Salinity

The SBE45 salinity data were calibrated against bench salinometer data from samples collected from the underway system during the cruise. The data from the SBE45 TSG at the discrete sampling times were compared with the bench salinometer measurements. The salinity offsets (bench - TSG) were plotted against date/time and bench salinity and outliers identified. The relationships in the offset between TSG and bench salinometer were then compared to the date/time and the bench salinity in separate linear regressions. There was a significant relationship of offset with date/time (R² = 0.43; n = 168; F = 127.3; p < 0.001) and also bench salinity (R² = 0.18; n = 168; F = 38.0; p < 0.001).

Applying the significant equation from the date/time regression with the higher R², the offset was generated at the date/time when the non-toxic underway system was switched on (30/09/2011 08:00 offset = -0.0151) and when switched off at the end of the cruise (09/11/2011 14:00 offset = 0.0017). The offset was applied for the period in between by linear interpolation of these offsets through the BODC BUDS calibration routine (BODC ICALRF 6729).

Fluorescence

The fluorometer voltage data were calibrated against extracted chlorophyll-a data from samples collected from the underway system during the cruise. Samples of seawater collected and extracted chlorophyll-a measurements made following Welschmeyer (1994). Each sample of 250 ml was filtered through a 47 mm 0.2 µm polycarbonate filter. The filters were then placed in a vial with 10 ml 90% acetone and left in a freezer for 24 hours. The samples were then analysed on a pre-calibrated Turner Designs Trilogy fluorometer with a non-acidified chl module (CHL NA #046) fitted. The bench fluorometer calibration was checked against dilutions of pure chlorophyll stock during the cruise and no modifications to the calibration were necessary. The raw voltage data from the fluorometer at the discrete sampling times were compared with the extracted chlorophyll-a measurements. The offsets (extracted chl-a - voltage) were plotted against date/time and extracted chlorophyll-a and outliers identified. Based on a preliminary calibration against extracted chl-a, which over stated the chlorophyll concentrations at the start of the cruise; it was decided to split the dataset for calibration. The calibration was split at the fluorometer cleaning event at 03/10/2011 13:04 in to two sections (1 and 2). The linear regression between the offset and extracted chlorophyll-a for each section were calculated. There was a significant relationship for both section 1 (R² = 0.16; n = 174; F = 33.5; p < 0.001) and section 2 (R² = 0.92; n = 174; F = 1880.7; p < 0.001).

Applying the equation from the extracted chlorophyll-a regression for each section, the calibrated fluorescence channel data were generated through the BODC BUDS calibration routine.

Section 1: 30/09/2011 08:00 to 03/10/2011 13:04 BODC ICALRF 6727 CPHLUT01 = 1.5771 * FVLTWS01 - 0.1038

Section 2: 03/10/2011 13:04 to 09/11/2011 14:00 BODC ICALRF 6728 CPHLUT01 = 3.3824 * FVLTWS01 - 0.1286

References

Welschmeyer N.A., 1994. Fluorometric analysis of chlorophyll-a in the presence of chlorophyll-b and phaeopigments. Limnology and Oceanography, 39:1985-1992.

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: