| Ocean carbon cycle and ocean acidification are hot research topics in ocean science,and total alkalinity(TA)data are essentials for these researches.In situ TA analyzers are the best tools for obtaining TA data of high temporal resolution.However,very few instruments are reported and they do not meet the requirements of research community.In this study,we improved our previously developed in situ analyzer for TA(ISA-TA),and tested its performance in the laboratory and on a testing platform at sea.The obtained results are as follows:(1)The structure of ISA-TA was optimized and some parts were redesigned.These parts include the cross-shaped quartz flow cell,the photoelectric detection system of high S/N ratio,the 2-position 8-port valve with reduced size,the peristaltic pump with motor whose shaft is extended at 2 ends,the controlling circuit,and the water-proof housing.After these modifications,ISA-TA is able to perform in-situ calibration with single standard,acquire salinity data from a CTD in real time,run autonomously without a host computer,and store data in an on-board memory.The modified ISA-TA has reduced size,weight and power consumption.(2)The testes in the laboratory show the performance of the modified ISA-TA was improved significantly.The linearity of calibration curves was improved;the measurement precision was±1.2 μmol/kg(n=126),the measurement accuracy was 3.0±1.3 μmol/kg.The empirical formulas for temperature calibration were proved to be effective.The single-standard calibration method was helpful in reducing the drift of ISA-TA.(3)Four tests and applications were carried out on the testing platform located in Tong’an bay,Xiamen.One of them lasted for 24 days.The results show that ISA-TA is able to run smoothly for a long time in the harsh marine environment.With the single-standard calibration,the best in-situ accuracy of ISA-TA was-0.1±7.7μmol/kg,which still needs to be improved.The tests and applications discovered that seawater TA,salinity and tidal height in the testing site were strongly coupled.(4)The ISA-TA is suitable for obtaining long-term time-series seawater TA,salinity and temperature,and it could be a powerful tool for the researches of oceanic processes related to TA. |
