Metadata Report for BODC Series Reference Number 1263720
Definition of BOTTFLAG
|0||The sampling event occurred without any incident being reported to BODC.|
|1||The filter in an in-situ sampling pump physically ruptured during sample resulting in an unquantifiable loss of sampled material.|
|2||Analytical evidence (e.g. surface water salinity measured on a sample collected at depth) indicates that the water sample has been contaminated by water from depths other than the depths of sampling.|
|3||The feedback indicator on the deck unit reported that the bottle closure command had failed. General Oceanics deck units used on NERC vessels in the 80s and 90s were renowned for reporting misfires when the bottle had been closed. This flag is also suitable for when a trigger command is mistakenly sent to a bottle that has previously been fired.|
|4||During the sampling deployment the bottle was fired in an order other than incrementing rosette position. Indicative of the potential for errors in the assignment of bottle firing depth, especially with General Oceanics rosettes.|
|5||Water was reported to be escaping from the bottle as the rosette was being recovered.|
|6||The bottle seals were observed to be incorrectly seated and the bottle was only part full of water on recovery.|
|7||Either the bottle was found to contain no sample on recovery or there was no bottle fitted to the rosette position fired (but SBE35 record may exist).|
|8||There is reason to doubt the accuracy of the sampling depth associated with the sample.|
|9||The bottle air vent had not been closed prior to deployment giving rise to a risk of sample contamination through leakage.|
Definition of Rank
No Problem Report Found in the Database
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."
The Niskin bottle is a device used by oceanographers to collect subsurface seawater samples. It is a plastic bottle with caps and rubber seals at each end and is deployed with the caps held open, allowing free-flushing of the bottle as it moves through the water column.
The standard version of the bottle includes a plastic-coated metal spring or elastic cord running through the interior of the bottle that joins the two caps, and the caps are held open against the spring by plastic lanyards. When the bottle reaches the desired depth the lanyards are released by a pressure-actuated switch, command signal or messenger weight and the caps are forced shut and sealed, trapping the seawater sample.
Lever Action Niskin
The Lever Action Niskin Bottle differs from the standard version, in that the caps are held open during deployment by externally mounted stainless steel springs rather than an internal spring or cord. Lever Action Niskins are recommended for applications where a completely clear sample chamber is critical or for use in deep cold water.
A modified version of the standard Niskin bottle has been developed for clean sampling. This is teflon-coated and uses a latex cord to close the caps rather than a metal spring. The clean version of the Levered Action Niskin bottle is also teflon-coated and uses epoxy covered springs in place of the stainless steel springs. These bottles are specifically designed to minimise metal contamination when sampling trace metals.
Bottles may be deployed singly clamped to a wire or in groups of up to 48 on a rosette. Standard bottles have a capacity between 1.7 and 30 L, while Lever Action bottles have a capacity between 1.7 and 12 L. Reversing thermometers may be attached to a spring-loaded disk that rotates through 180° on bottle closure.
RAPID Cruise D279 discrete nutrient sampling by originator Landolfi
Nutrient data from D279 were collected and analysed by two originators working closely together. The full CTD sample data set of nitrate+nitrite (hereinafter nitrate), phosphate and silicate was provided by Dr Richard Sanders. Further nutrient data, including a subset of the data provided by Dr Richard Sanders, were provided by Dr Angela Landolfi. Differences between the full CTD data set and the data subset only occur in the nitrate data due to post cruise calibrations that were performed. As such, the data acquisition, onboard analysis and onboard data quality are identical. Dr Angela Landolfi also provided data from plastic carboy samples that were collected during the cruise. Data described below were supplied by Dr Angela Landolfi.
Originator's data acquisition and analysis
Onboard processing and analysis
Inorganic nutrient concentrations nitrate, phosphate and silicate were measured immediately onboard using a Skalar San Plus autoanalyser according to standard colorimetric techniques (Kirkwood, 1995) with the exception that the pump rates through the phosphate line were increased by a factor of 1.5, which improves reproducibility and peak shape.
Samples were drawn from Niskin bottles into 25ml sterilin coulter counter vials and kept refrigerated at 4°C until analysis, which commenced within 24 hours. At 9 stations, samples were also taken from the surface in 25l high density plastic carboys. Stations were run in batches of 2-6 with most runs containing 3 or 4 stations. Overall, 34 runs were undertaken. An artificial seawater matrix (ASW) of 40 g/l sodium chloride was used as the intersample wash and standard matrix. The nutrient free status of this solution was checked by running Ocean Scientific International (OSI) nutrient free seawater on every run.
In a departure from previous methodology, a single set of mixed standards were made up at the start of the cruise and used throughout the cruise. These were made by diluting 5 mM solutions made from weighed dried salts in 1 litre of ASW into plastic 1 litre volumetric flasks that had been cleaned by soaking for 6 weeks in MQ water. This was in an effort to minimise the run to run variability in concentrations observed on previous cruises. OSI nutrient standard solutions were used sporadically during the cruise to monitor the degradation of these standards.
Data were transferred to another computer initially using a zip disk, and then after station 66 by means of a memory stick. The zip disk transfer route was unreliable and resulted in a delay between sample analysis and data work up of 8-10 stations. After station 66, data were worked up immediately. This delay had the effect that the problems with the nitrate line described below could not be evaluated in close to real time.
Data processing was undertaken using Skalar proprietary software. Generally this was straightforward, however a detailed examination of nitrate data from stations 20-60 was needed to achieve acceptable calibrations and bulk nutrient values. The wash time and sample time were 90 seconds, and the lines were washed daily with 0.25M NaOH (P) and 10% Decon (N, Si). Time series of baseline, bulk standard concentration, instrument sensitivity, calibration curve correlation coefficient, nitrate reduction efficiency and duplicate difference were compiled and updated on a daily basis.
Problems with the analyser
1) In the early part of the cruise on runs 1-3 (stations 2-21), the phosphate baseline suffered frequent catastrophic baseline degradations. All the samples were rerun, but duplicates could not be run as the available duplicate time was used to reanalyse samples. This was alleviated mid run by removing the flow cell and shaking it vigorously, and eliminated over the longer term by refitting some elements of the line and reducing the pull through rate. Stations 49-52 were also affected by this problem and no phosphate data are available for stations 51 and 52. Stations 71-74 were compromised by a failure of the temperature water bath. These stations were reanalysed 24 hours later using samples from salinity bottles.
2) The nitrate line was very noisy between stations 22 and 60. Initially this was suspected to be due to a fault with the reagents, which were renewed several times. However, after this failed to rectify the situation, the cadmium column was repacked on two occasions. This also failed to rectify the situation and a new cadmium column was therefore fitted, which gave no problems during the rest of the cruise. Stations 22-60 were reprocessed to give bulk nutrient values in line with those from the remainder of the stations. The effect of this on data quality has yet to be systematically evaluated.
Analyser performanceThe performance of the autoanalyser is monitored via the following parameters: baseline value, calibration curve slope, regression coefficient of the calibration curve and nitrate reduction efficiency.
The instrument sensitivity for nitrate varied widely and unpredictably during the cruise by up to 40%. Phosphate and silicate sensitivity behaved much more reproducibly, with these parameters varying by about 10% over the 5 week period of observations.
The quality of the calibration curves was generally good with 95% having regression coefficients better than 0.999. The reduction efficiency of the cadmium column was <100% during the early part of the cruise. The column was changed at station 66, after which the efficiency increased to approximately 100%.
The baseline value of the instrument barely changed throughout the cruise, with the exception of phosphate, which declined after the first run from 6300 to about 5900.
Post cruise processing and analysis
To improve the sensitivity of the NO3 (nitrite) detection, some baseline analysis and thus recalibration of the nitrate data was performed once back from the cruise (during the cruise the calibrations are done automatically by the autoanalyser software).
Samples for Total Nitrogen (TN) and Total Phosphorus (TP) analysis were carefully collected directly from Niskin bottles into 60-ml sterile high density polythene bottles. Sample bottles were rinsed three times with their own volume of sample and immediately frozen. These samples were not filtered.
Where samples for the determination of TN and TP have been UV-oxidised in duplicates, the duplicates standard deviation (SD) is given. If the SD > TN/TP value, then the sample has been classified as Not Determined (ND).
Total Nitrogen (TN) was analysed by two methods: 1) High Temperature Pt Catalytic Oxidation (HTCO); and 2) UV oxidation.
HTCO was performed with a Shimadzu 5000A DOC analyser connected to a Antek 705E chemiluminescent nitrogen specific detector. UV oxidation uses high intensity ultraviolet light at a wavelength below 250 nm in a Metrohom UV705 digester. The HTCO method is known to give higher recoveries as compared with the UV method (Bronk et al., 2000). Further details on these methods can be found in Landolfi (2005). The oxidation occurred within 4 months of collection for the HTCO method. Analysis by the UV oxidation method occurred more than 6 months after collection.
Total Organic Nitrogen (TON) was then derived by subtracting the inorganic nitrate from the total nitrogen (TN).
Total phosphorus (TP) was analysed by first converting the phosphorus into phosphate by using high intensity ultraviolet light at a wavelength below 250 nm in a Metrohom UV705 digester using a modified version of the method used by Sanders and Jickells (2000). Samples were then analysed for phosphate according to standard colorimetric techniques using a Skalar San Plus autoanalyser (Kirkwood et al., 1996).
Total Organic Phosphorus (TOP) was then derived by subtracting the inorganic phosphate from the total phosphorus (TP).
Bronk, D. A., Lomas, M. W., Glibert, P. M., Schukert, K. J., and Sanderson, M. P., 2000. Total dissolved nitrogen analysis: Comparisons between the persulfate, UV and high temperature oxidation methods. Marine Chemistry, 69, 163-178.
Kirkwood, D. S., 1995. Nutrients: Practical notes on their determination in seawater. ICES Techniques in Marine Environmental Science report 17, International Council for the Exploration of the Sea, Copenhagen. 25p. ISSN 0903-2606.
Kirkwood, D. S., Aminot, A., and Carlberg, S. R., 1996. The 1994 quasimeme laboratory performance study: Nutrients in seawater and standard solutions. Marine Pollution Bulletin, 32, 640-645.
Landolfi, A., 2005. The importance of Dissolved organic nutrients in the biogeochemistry of oligotrophic gyres. PhD thesis, School of Ocean and Earth Sciences, University of Southampton, Southampton, UK.
Landolfi, A., Oschlies, A., and Sanders, R., 2008. Organic nutrients and excess nitrogen in the North Atlantic subtropical gyre. Biogeosciences, 5, 1199-1213.
Sanders, R. and Jickells, T., 2000. Total organic nutrients in Drake Passage. Deep Sea Research Part I: Oceanographic Research Papers, 47(6), 997-1014.
BODC data processing procedures
|Originator's parameter||Description||Units||BODC parameter code||Units||Comments|
|TN_HTCO||Total Nitrogen derived from HTCO||µmol/l||NTOTWCHT||µmol/l||Analysed using a Platinum (Pt) catalyst|
|TN_UV||Total Nitrogen derived from UV oxidation||µmol/l||NTOTWCTX||µmol/l||-|
|SD_TN_UV||Standard deviation of Total Nitrogen derived from UV oxidation||µmol/l||SDNTWCTX||µmol/l||-|
|TON||Total Organic Nitrogen||µmol/l||-||µmol/l||Not stored. Can be derived from subtracting Nitrate+Nitrite from Total Nitrogen derived from HTCO analysis.|
|TOP||Total Organic Phosphorus||µmol/l||-||µmol/l||Not stored. Can be derived from subtracting Phosphate from Total Phosphorus|
|SD_TP||Standard deviation of Total Phosphorus||µmol/l||SDTPHP01||µmol/l||-|
The data were supplied in ASCII format. Units were converted, if necessary, to the BODC standard parameter units.
Quality control flags that were used by the originator have been mapped to BODC flags as shown below:
|Originator flag||Description||BODC flag||Comments|
|C||Suspected contamination of sample||L||-|
|ND||Not determined||N||These data have not been loaded into the database|
The data were then loaded into the project database under the ORACLE Relational Database Management System without modification.
Data that lay outside the permitted range for the parameter code were flagged suspect.
Originator's onboard data quality
Precision of measurements
Internal consistency of measurementsThis was evaluated by using a deep water sample taken on station 1 and was run on every station.
Accuracy of measurements
The short term precision of the measurements was evaluated by running one or two duplicate samples per station (thus 3-6 per run). The mean differences for silicate, nitrate and phosphate were 0.67, 1.63 and 2.04%, respectively. However, this conceals substantial variability in both nitrate and phosphate precision during the cruise. A group of stations from approximately 25- 60 had poor nitrate precision but the precision of the phosphate analyses improved over the course of the cruise from about 5% to about 1%.
Nitrate concentration appeared to be invariant whereas the phosphate and silicate concentrations declined markedly over the cruise. The variability of bulk nutrient concentration from the mean is indicative of the internal consistency of the data set. For nitrate this is simple to evaluate, as the concentration appeared to be invariant. The residual concentration appears to be normally distributed and shows no significant trend over time. The absolute average residual value was 0.27 micromoles per litre or 1.2%.
For phosphate and silicate, a linear function was fitted which predicted concentration as a function of elapsed day. This regression was used to generate values for phosphate and silicate for each day and the residual difference calculated.
Both phosphate and silicate residuals appear to have a normal distribution, with silicate (and to a lesser extent phosphate) residuals displaying a sinusoidal pattern with time for unknown reasons. The mean residual values are 0.12 micromoles per litre or 1.17% for silicate and 0.03 micromoles per litre or 2.1% for phosphate.
The accuracy was monitored by the use of OSI nutrient standard solutions, which need to be diluted by the user. The analysis of these standards gave values of phosphate 1.01 +/- 0.02 micromoles per litre for a nominally 1 micromolar solution, nitrate 10.9 +/- 0.13 for a nominally 10 micromolar solution and silicate 21.4 +/- 0.1 micromoles per litre for a nominally 20 micromolar solution. These imply that the nitrate and silicate results are too low by about 10% and 5% respectively. The standards used on this cruise have been retained for further investigation and a comparison with historical data will also be used to address this issue.
Originator's post cruise data quality
TN samples determined by the UV-oxidation method are suspected to be biased towards higher values due to the analysis carried out at a later stage (> 6 months after collection).
Rapid Climate Change (RAPID) Programme
Rapid Climate Change (RAPID) is a £20 million, six-year (2001-2007) programme of the Natural Environment Research Council (NERC). The programme aims to improve our ability to quantify the probability and magnitude of future rapid change in climate, with a main (but not exclusive) focus on the role of the Atlantic Ocean's Thermohaline Circulation.
- To establish a pre-operational prototype system to continuously observe the strength and structure of the Atlantic Meridional Overturning Circulation (MOC).
- To support long-term direct observations of water, heat, salt, and ice transports at critical locations in the northern North Atlantic, to quantify the atmospheric and other (e.g. river run-off, ice sheet discharge) forcing of these transports, and to perform process studies of ocean mixing at northern high latitudes.
- To construct well-calibrated and time-resolved palaeo data records of past climate change, including error estimates, with a particular emphasis on the quantification of the timing and magnitude of rapid change at annual to centennial time-scales.
- To develop and use high-resolution physical models to synthesise observational data.
- To apply a hierarchy of modelling approaches to understand the processes that connect changes in ocean convection and its atmospheric forcing to the large-scale transports relevant to the modulation of climate.
- To understand, using model experimentation and data (palaeo and present day), the atmosphere's response to large changes in Atlantic northward heat transport, in particular changes in storm tracks, storm frequency, storm strengths, and energy and moisture transports.
- To use both instrumental and palaeo data for the quantitative testing of models' abilities to reproduce climate variability and rapid changes on annual to centennial time-scales. To explore the extent to which these data can provide direct information about the thermohaline circulation (THC) and other possible rapid changes in the climate system and their impact.
- To quantify the probability and magnitude of potential future rapid climate change, and the uncertainties in these estimates.
Overall 38 projects have been funded by the RAPID programme. These include 4 which focus on Monitoring the Meridional Overturning Circulation (MOC), and 5 international projects jointly funded by the Netherlands Organisation for Scientific Research, the Research Council of Norway and NERC.
The RAPID effort to design a system to continuously monitor the strength and structure of the North Atlantic Meridional Overturning Circulation is being matched by comparative funding from the US National Science Foundation (NSF) for collaborative projects reviewed jointly with the NERC proposals. Three projects were funded by NSF.
A proportion of RAPID funding as been made available for Small and Medium Sized Enterprises (SMEs) as part of NERC's Small Business Research Initiative (SBRI). The SBRI aims to stimulate innovation in the economy by encouraging more high-tech small firms to start up or to develop new research capacities. As a result 4 projects have been funded.
Monitoring the Meridional Overturning Circulation at 26.5N (RAPIDMOC)
There is a northward transport of heat throughout the Atlantic, reaching a maximum of 1.3PW (25% of the global heat flux) around 24.5°N. The heat transport is a balance of the northward flux of a warm Gulf Stream, and a southward flux of cooler thermocline and cold North Atlantic Deep Water that is known as the meridional overturning circulation (MOC). As a consequence of the MOC northwest Europe enjoys a mild climate for its latitude: however abrupt rearrangement of the Atlantic Circulation has been shown in climate models and in palaeoclimate records to be responsible for a cooling of European climate of between 5-10°C. A principal objective of the RAPID programme is the development of a pre-operational prototype system that will continuously observe the strength and structure of the MOC. An initiative has been formed to fulfill this objective and consists of three interlinked projects:
- A mooring array spanning the Atlantic at 26.5°N to measure the southward branch of the MOC (Hirschi et al., 2003 and Baehr et al., 2004).
- Additional moorings deployed in the western boundary along 26.5°N (by Prof. Bill Johns, University of Miami) to resolve transport in the Deep Western Boundary Current (Bryden et al., 2005). These moorings allow surface-to-bottom density profiles along the western boundary, Mid-Atlantic Ridge, and eastern boundary to be observed. As a result, the transatlantic pressure gradient can be continuously measured.
- Monitoring of the northward branch of the MOC using submarine telephone cables in the Florida Straits (Baringer et al., 2001) led by Dr Molly Baringer (NOAA/AOML/PHOD).
The entire monitoring array system created by the three projects will be recovered and redeployed annually until 2008 under RAPID funding. From 2008 until 2014 the array will continue to be serviced annually under RAPID-WATCH funding.
The array will be focussed on three regions, the Eastern Boundary (EB), the Mid Atlantic Ridge (MAR) and the Western Boundary (WB). The geographical extent of these regions are as follows:
- Eastern Boundary (EB) array defined as a box with the south-east corner at 23.5°N, 25.5°W and the north-west corner at 29.0°N, 12.0°W
- Mid Atlantic Ridge (MAR) array defined as a box with the south-east corner at 23.0°N, 52.1°W and the north-west corner at 26.5°N, 40.0°W
- Western Boundary (WB) array defined as a box with the south-east corner at 26.0°N, 77.5°W and the north-west corner at 27.5°N, 69.5°W
Baehr, J., Hirschi, J., Beismann, J.O. and Marotzke, J. (2004) Monitoring the meridional overturning circulation in the North Atlantic: A model-based array design study. Journal of Marine Research, Volume 62, No 3, pp 283-312.
Baringer, M.O'N. and Larsen, J.C. (2001) Sixteen years of Florida Current transport at 27N Geophysical Research Letters, Volume 28, No 16, pp3179-3182
Bryden, H.L., Johns, W.E. and Saunders, P.M. (2005) Deep Western Boundary Current East of Abaco: Mean structure and transport. Journal of Marine Research, Volume 63, No 1, pp 35-57.
Hirschi, J., Baehr, J., Marotzke J., Stark J., Cunningham S.A. and Beismann J.O. (2003) A monitoring design for the Atlantic meridional overturning circulation. Geophysical Research Letters, Volume 30, No 7, article number 1413 (DOI 10.1029/2002GL016776)
|Principal Scientist(s)||Stuart A Cunningham (Southampton Oceanography Centre)|
Complete Cruise Metadata Report is available here
No Fixed Station Information held for the Series
The following single character qualifying flags may be associated with one or more individual parameters with a data cycle:
|<||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.)|
|E||End of CTD Down/Up Cast|
|G||Non-taxonomic biological characteristic uncertainty|
|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|
|O||Improbable value - user quality control|
The following single character qualifying flags may be associated with one or more individual parameters with a data cycle:
|0||no quality control|
|2||probably good value|
|3||probably bad value|
|6||value below detection|
|7||value in excess|
|A||value phenomenon uncertain|
|Q||value below limit of quantification|