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An automated analyzer was developed to achieve fast, precise, and accurate measurements of seawater total alkalinity (A T ) based on single-point titration and spectrophotometric pH detection. The single-point titration was carried out in a circulating loop, which allowed the titrant (hydrochloric acid and bromocresol green solution) and a seawater sample to mix at a constant volume ratio. The dissolved CO 2 in the sample−titrant mixture was efficiently removed by an inline CO 2 remover, which consists of a gas-permeable tubing (Teflon AF2400) submerged in a sodium hydroxide (NaOH) solution. The pH of the mixture was then measured with a custom-made spectrophotometric detection system. The analyzer was calibrated against multiple certified reference materials (CRMs) with different A T values. The analyzer features a sample throughput time of 6.5 min with high precision (±0.33−0.36 μmol kg −1 ; n = 48) and accuracy (−0.33 ± 0.99 μmol kg −1 ; n = 10). Intercomparison to a traditional open-cell A T titrator showed overall good agreement of 0.88 ± 2.03 μmol kg −1 (n = 22). The analyzer achieved excellent stability without recalibration over 11 days, during which time 320 measurements were made with a total running time of over 40 h. Because of its small size, low power consumption requirements, and its ability to be automated, the new analyzer can be adapted for underway and in situ measurements. ■ INTRODUCTIONAs a measure of seawater buffering capacity, total alkalinity (A T ) of a seawater sample is defined as "the number of moles of hydrogen ion equivalent to the excess of proton acceptors (bases formed from weak acids with a dissociation constant K ≤ 10 −4.5 at 25°C and zero ionic strength) over proton donors (acids with K > 10 −4.5 ) in 1 kg of sample". 1 Observations of A T are extremely useful in identifying and assessing physical and biogeochemical processes in the ocean, such as inventory of anthropogenic CO 2 , calcification by shell-building organisms, dissolution/precipitation of calcium carbonate minerals, aerobic versus anaerobic respiration, and water mixing.2−6 As one of the four primary parameters of the marine CO 2 system, A T can be used with one of the other three parameters, pH, pCO 2 , and total dissolved inorganic carbon (DIC), to fully characterize the seawater−carbonic system through thermodynamic calculations. 7,8 In many ocean carbon studies, the required precision and accuracy of seawater A T measurements are stringent (<0.2%) because of the high background values (mean seawater A T ∼ 2300 μmol kg −1 ) compared to relatively small natural variations.The traditional method for high-precision, high-accuracy measurements of seawater A T involves a multi-point potentiometric titration in an open or a closed cell.9,10 It uses a stepwise addition of a strong acid [hydrochloric acid (HCl)] to a known amount of seawater in a titration cell. The titration is monitored using a pH electrode, and the A T is computed from the equivalence point located by a nonlinear least-squares or Gran fun...

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