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...

Carbon dioxide partial pressure (pCO 2) in surface water was continuously measured every 3 h from July 2012 to June 2013 using an autonomous pCO 2 system (MAPCO 2) deployed on a moored buoy on the East China Sea shelf (31 N, 124.5 E). Sea surface pCO 2 and pH had the largest variations in summer, ranging from 215 to 470 μatm, and 7.941 to 8.263 (averagely 8.084 ± 0.080), respectively. They varied little in winter, ranging from 328 to 395 μatm, and 8.003 to 8.074 (averagely 8.052 ± 0.010), respectively. The seasonal average sea surface pCO 2 was respectively 335 ± 70 μatm, 422 ± 43 μatm, 362 ± 11 μatm, and 311 ± 59 μatm in summer, autumn, winter, and spring, and was overall undersaturated with respect to atmosphere on a yearly basis. Although the average sea surface pCO 2 in summer was below the atmospheric level, the net CO 2 flux has suggested a CO 2 source status due to the influence of typhoon. Our observation thus demonstrated the significant, even dominant impact of episodic typhoon events on surface ocean CO 2 chemistry and air-sea CO 2 gas exchange, which would be impossible to capture by shipboard observation. The high wind stress and curl associated with the northward movement of typhoon induced complex sea surface water movement, vertical mixing, and subsequent biological drawdown, which differed in pre-, onset, and post-typhoon stages. Based on our estimates, the degassing fluxes during typhoon reached as high as 82 mmol m −2 CO 2 and 242 mmol m −2 CO 2 in summer and autumn, respectively, accounting for twice as large as the summer CO 2 sink during non-typhoon period, and 28% of the total CO 2 source in autumn.

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Lanthanum aminopolycarboxylates, Na12n[La(edta)L]4n·8nNaCl·4nH2O (1: L = HPO32−; 2: L = CO32−) and K12n[La(cdta)(CO3)]4n·35nH2O (3), with square structures were obtained. Carbonate 2 possesses 3.7 Å diameter holes that can adsorb a small amount of O2 or CO2 selectively.