Development And Sea Trial Study Of Electrochemical Sensors For Seafloor Hydrothermal Vent

In recent years, application of chemical sensors in in-situ measurement has attracted more and more attentions in marine science. This study is focused on the preparation improvement, lab-test of pH electrode, and application of lab-developed multi-parameter chemical sensors in in-situ measurements in deep-sea and shallow water hydrothermal systems.pH is a fundamental parameter in understanding the chemical processes in hydrothermal vents and diffuse flow systems. Hence, accurate access of in-situ pH is a common concern of marine scientists. Although signals have been acquired by the former pH electrodes, the drifting problem greatly constrain the application of them. Improvements on preparation of IrOx electrode have been proposed based on the mechanism of molten alkali metal carbonate. Results of lab-experiments and SEM surface analysis indicate that the response characteristics of the improved IrOx electrode are better, including good reproducibility and sensitivity, small OCP(open circuit potential) drift (<5mV) of7-day continuous measurement, long life time and remarkable agreement with respect to potential/pH slopes and apparent standard electrode potentials of electrodes from the same batch. Good results of lab-test permit IrOx electrode prepared by molten mixed carbonate lithium with sodium peroxide be suitable for in-situ pH measurement at pressures up to50MPa and temperatures up to90℃. Furthermore, the IrOx electrode could be potentially used at temperatures up to150℃.Based on the good results of lab-test, multi-parameter chemical sensor, which integrates Eh, Ag/Ag2S and pH electrode, has been applied in several marine investigations, including hydrothermal detection in deep-sea and shallow water systems. During applications in DY115-20Cruise, Dayangyihao Research Vessel, multi-parameter chemical sensor has measured60times in both East Pacific Ridge (EPR) and Southwest Indian Ridge (SWIR). Among the60measurements,55groups of valid data were gained, in which29records indicate potential active hydrothermal vents. Besides, the electrodes exhibit good sensitivity, stability and long lifetime during the six-month measurements. Multi-parameter chemical sensor system has become a common instrument in Dayangyihao Research Vessel. During the investigation on detecting hydrothermal vents in Kueishan Tao area, batches of valid chemical data, which are in good agreement with anomalies caused by hydrothermal vent fluids, were acquired by the multi-parameter sensor chain. Potential spots of new hydrothermal vents have been inferred according to the in-situ chemical measurements. It has been proved by sea trial results on many occasions that the multi-parameter chemical sensor can help detecting the chemical anomalies of the plumes. The chemical sensor system is an effective tool in hydrothermal activity detection.Chemical sensor system integrating Eh and pH electrodes was used to measure the structure of hydrothermal plume at shallow-water hydrothermal vents in Kueishan Tao area, Taiwan. Three dimensional distributions of pH and Eh were firstly acquired at two typical types of hydrothermal plumes. Investigation reveals that the influence of hydrothermal is not limited in vicinity of hydrothermal vents, but on the total water column with most pronounced layers at the surface.