Measurement of total alkalinity of surface waters using a continuous flowing spectrophotometric technique

Mary P. Roche, Frank J Millero

Research output: Contribution to journalArticle

13 Citations (Scopus)

Abstract

Methodology and instrumentation are described which were used for continuous measurement of total alkalinity (TA) in surface seawater during a Joint Global Ocean Flux Study (JGOFS) cruise in the Indian Ocean. The procedure involves a single step acid addition of HCl to a known volume of seawater with rapid spectrophotometric measurement of pH (3 to 4) and calculation of the TA after stripping out the CO2. The flowing total alkalinity system (FLTA) consists of a calibrated volumetric pipette (~ 100 cm3), a thermosrated mixing cell (~ 200 cm3), a computerized piston titrator, a platinum thermometer, and a Hewlett Packard diode array spectrophotometer with a flowing spectrophotometric cell as the detector. All the electronic components have interfaces which are easily connected to a personal computer and manipulated using a Quick Basic program. The FLTA system makes continuous measurements of TA from the shipboard flowing seawater line. Laboratory results (N = 127) on Gulf Stream seawater (GSSW) have shown a precision within ±2-3 μmol kg-1 in TA. Certified reference materials (CRMs) measured at sea (N = 14) gave precise total alkalinities to ±2.2 μmol kg-1. Intercomparison of the total alkalinity of underway surface samples (N = 16) obtained in the Indian Ocean using potentiometric and spectrophotometric titration systems gives average differences of ±3 μmol kg-1 in TA. The agreement between the two methods is very good considering the temporal and spatial differences in the sampling. The continuous measurement of TA using the FLTA system may reflect small variations of TA in the surface waters of the oceans which would not be visible when measuring TA in samples taken from CTD casts at individual stations. These data can also be combined with flowing pH or p(CO2) data to fully characterize the carbonate system in surface waters.

Original languageEnglish (US)
Pages (from-to)85-94
Number of pages10
JournalMarine Chemistry
Volume60
Issue number1-2
DOIs
StatePublished - Feb 1998

Fingerprint

Alkalinity
Surface waters
alkalinity
surface water
Seawater
seawater
carbonate system
Thermometers
Carbonates
Spectrophotometers
global ocean
Platinum
Titration
platinum
Personal computers
Pistons
instrumentation
Diodes
Fluxes
Sampling

Keywords

  • Alkalinity
  • Carbon
  • Instrumentation
  • pH
  • Spectrophotometry

ASJC Scopus subject areas

  • Chemistry(all)
  • Oceanography

Cite this

Measurement of total alkalinity of surface waters using a continuous flowing spectrophotometric technique. / Roche, Mary P.; Millero, Frank J.

In: Marine Chemistry, Vol. 60, No. 1-2, 02.1998, p. 85-94.

Research output: Contribution to journalArticle

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