DIC and Total alkalinity at the E1 site of WCO 2010-2019 for Cruise WCO
Originator's Protocol for Data Acquisition and Analysis
Sampling methodology
Borosilicate glass bottles with ground glass stoppers (50 mL) were used to collect seawater from the Niskin bottles for Dissolved Inorganic Carbon (CT) and Total Alkalinity (AT) analysis. Sample bottles were rinsed and filled according to standard procedures detailed in Dickson et al. (2007). Samples were poisoned with 10 µL mercuric chloride for storage. Samples were returned to PML for analysis.
Analytical methodology
CT was measured using a Dissolved Inorganic Carbon Analyser (Apollo SciTech, Model AS-C3). The analyser adds a strong acid (10% H 3 PO 4 plus 10% NaCl solution) causing carbon species within the seawater to be converted to CO 2 gas, which is purged from the sample by pure nitrogen (N 2 ) carrier gas, is dried and cooled to reduce water vapour. The concentration of the dried CO 2 gas is measured with a LICOR LI-7000 CO 2 analyser. The total amount of CO 2 is quantified as the integrated area under the concentration-time curve, and converted to DIC using a standard curve created by analysing known concentrations of the Certified Reference Materials (Dickson CO 2 CRMs). A measurement volume of 0.75 mL was used, with up to 5 measurements made from each sample. Values outside a 0.1 % range were excluded from the final result. Duplicate measurements provided an estimate of measurement error < 0.1 %. CT was corrected for the addition of mercuric chloride.
AT was measured using the open-cell potentiometric titration method (Dickson et al. 2007) on 12 mL sample volumes using an automated titrator (Apollo SciTech Alkalinity Titrator Model AS-ALK2). Calibration was made using Certified Reference Materials (Dickson CO 2 CRMs). Duplicate measurements were made for each sample, and the estimate of measurement error < 0.5 %. AT was corrected for the addition of mercuric chloride.
pH, pCO2, Calcite saturation, Aragonite saturation, HCO3 and CO3 are calculated from DIC, total alkalinity, salinity, temperature, total phosphate and total silicate (taken from the WCO nutrient dataset), therefore, the following data collection instruments were used to derive these parameters: Sea-Bird SBE 911 CTD; Apollo SciTech AS-C3 Dissolved Inorganic Carbon (DIC) analyser; Apollo SciTech AS-ALK2 total alkalinity titrator.
References Cited
Dickson A.G., Sabine C.L. and Christian J.R., 2007. Guide to best practices for ocean CO2 measurements. PICES Special Publication 3. 191 pp.
BODC Data Processing Procedures
Data received were loaded into the BODC database using established BODC data banking procedures. A parameter mapping table is provided below:
| Originator's Variable | Originator's Units | BODC Parameter Code | BODC Unit | Comments |
|---|---|---|---|---|
| CT SD | micro-mol/kg | TCO2SDK2 | umol/kg | - |
| CT | micro-mol/kg | TCO2KG02 | umol/kg | - |
| AT | micro-mol/kg | ALKYPOTK | umol/kg | - |
| Temp | degC | TEMPST01 | degC | - |
| Sal | dimensionless | PSALST01 | Dmnless | - |
| AT SD | micro-mol/kg | ALSDPOTK | umol/kg | - |
| pH | PHTLWCAL | pH units | - | |
| pH SD | PHTLSDWC | pH units | - | |
| pCO2 | uatm | PCO2WCAL | uatm | - |
| pCO2 SD | uatm | PCSDWCAL | uatm | - |
| CalSat | CLCTWCAL | Dmnless | - | |
| CalSat SD | CLSDWCAL | Dmnless | - | |
| ArgSat | ARGTWCAL | Dmnless | - | |
| ArgSat SD | ARSDWCAL | Dmnless | - | |
| HCO3 | umol/kg | BCRBWCAL | umol/kg | - |
| HCO3 SD | umol/kg | BCSDWCAL | umol/kg | - |
| CO3 | umol/kg | CRBTWCAL | umol/kg | - |
| CO3 SD | umol/kg | CRSDWCAL | umol/kg | - |
Data Quality Report
WOCE quality flags were implemented by data originators. These were converted to BODC quality flags - WOCE flags 1 and 2 were set to null, WOCE flags 3 and 5 were set to L.
Data originators advised that data reported on 02/12/2014 should have been reported as on 01/12/2014, and that data reported on 08/10/2016 should be removed from the dataset as the date could not be matched to an existing WCO cruise.
