D379 measurements of DIC and TA from CTD bottle samples
Originator's Protocol for Data Acquisition and Analysis
This dataset contains 464 measurements of dissolved inorganic carbon (DIC) and 461 measurements of total alkalinity (TA) in seawater. The samples were collected during RRS Discovery cruise D379 as part of the Extended Ellett Line in 2012 in the North-East Atlantic between Scotland and Iceland. Water samples were collected across 52 CTD stations from Niskin bottles attached to a stainless steel CTD rosette system.
The analysis of DIC was undertaken at the National Oceanography Centre, Southampton using a VINDTA 3C (Marianda, Germany, unit 11 and unit 24). By reaction with phosphoric acid, dissolved inorganic carbon of the sample is converted to CO 2 . The CO 2 gas is carried by N 2 into the coulometer cell to react with monoethanolamine and form a titratable acid. This causes the fading of the blue indicator. Responding to the colour change, a current flow generates base to remove the acid and restore the indicator to the original colour. The amount of CO 2 can be estimated from the required coulombs of the current required to achieve this (corrected for blank), and DIC concentration can then be calculated given the known sample volume.
The analysis of TA was also undertaken at NOC Southampton using the VINDTA 3C, using the non-linear curve fitting (least squares) approach as described in Dickson et al. (2007). This involves titration with HCl (approximately 0.10 mol/l) using an open cell, with a pH half cell electrode (glass bodied Orion 8101SC, Ross, USA) and an Ag/AgCl reference electrode (model 6.0729.100, Metrohm, Switzerland).
In order to standardise the results, Certified Reference Materials (CRM) from A.G. Dickson, Scripps Institution of Oceanography were analysed as standards to calibrate the instrument at the beginning and end of each day of analysis. A daily correction factor was applied to all measured values according to Millero et al. (1998).
Further details of the methodology can be found in the cruise report
References
Dickson, A. G. et al. , (2007) Guide to best practices for ocean CO 2 measurements, PICES Special Publication 3, pp. 191
Millero, F. J. et al. , (1998) Assessment of the quality of the shipboard measurements of total alkalinity on the WOCE Hydrographic Program Indian Ocean CO2 survey cruises 1994?1996, Mar. Chem., 63, 9?20
BODC Data Processing Procedures
Data were provided to BODC in an xlsx file. The file contained discrete bottle measurements at bottle firing depths. Replicate samples were averaged and standard deviations calculated. The measurements were loaded into the BODC database using established BODC data banking procedures. The originator's parameters were mapped to appropriate BODC parameter codes as shown below:
| Originator's variable | Units | BODC code | Description | Units | Comments |
| Dissolved Inorganic Carbon (DIC) | µmol/kg | TCO2MSXX | Concentration of total inorganic carbon {TCO2 CAS 7440-44-0} per unit mass of the water body [dissolved plus reactive particulate phase] | µmol/kg | - |
| DIC standard deviation | µmol/kg | TCO2MSSD | Concentration standard deviation of total inorganic carbon {TCO2 CAS 7440-44-0} per unit mass of the water body [dissolved plus reactive particulate phase] | µmol/kg | - |
| Total Alkalinity (TA) | µmol/kg | MDMAP014 | Total alkalinity per unit mass of the water body | µmol/kg | - |
| TA standard deviation | µmol/kg | MDMASD14 | Total alkalinity standard deviation per unit mass of the water body | µmol/kg | - |
Data Quality Report
None
Problem Report
None
