Oceanic Carbon Dioxide
Quality Control
Analytical Methods
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For methods used on a particular batch, please see its individual analysis by clicking on the batch link located on the Batch Information page.

Salinity

The salinity was determined by measuring its conductivity relative to IAPSO Standard Sea Water using a Guildline Autosal® Model 8400 conductive salinometer. The procedure is described in an in-house technical manual of the Oceanographic Data Facility, Scripps Institution of Oceanography, entitled, "Autosal Operating Procedures", dated December 10, 1993, revised January 10, 1994.
Total dissolved inorganic carbon
The total dissolved inorganic carbon was assayed in Dr. C. D. Keeling's laboratory at the Scripps Institution of Oceanography by the vacuum extraction/manometric procedure. The weighed sample is acidified with phosphoric acid; the CO2 evolved is then extracted under vacuum and condensed in a trap cooled by liquid nitrogen. The water and CO2 are separated from one another by sublimation and the CO2 is transferred into an electronic constant-volume manometer [ECM]. There its pressure, volume and temperature are measured and the amount of CO2 separated is computed from the virial equation of state.

Alkalinity
The total alkalinity was assayed by a two-stage, potentiometric, open-cell titration using coulometrically analyzed hydrochloric acid. A weighed sample of reference material is acidified to a pH between 3.5 and 4.0 with an aliquot of titrant. The solution is stirred for a period of time to allow the evolved CO2 to escape. The titration is then continued to a pH of about 3.0 and the equivalence point evaluated from titration points in the pH region 3.0 - 3.5 using a modified Gran procedure that corrects for the reactions with sulfate and fluoride ions.

Nutrients
Nutrient levels were determined using a modified 4-channel autoanalyzer. The procedures are similar to those described in Gordon, L.I., J.C. Jennings, A.A. Ross, J.M. Krest (1993) "A Suggested Protocol for Continuous Flow Automated Analysis of Sea Water Nutrients (Phosphate, Nitrate, Nitrite, and Silicic Acid) in the WOCE Hydrographic Program and the Joint Global Ocean Fluxes Study," WOCE Operations Manual, WHP Office Report WHPO 91-1 (rev. Nov. 1994).