Preparation And Application Of In-situ Geochemical Sensors On Seafloor

There are abundant strategic metal resources, energy sources and biological resources in International seabed area. It is an important supporting system for human life maintaining and sustainable social development. Seafloor hydrothermal system no only have potential tremendous economic value but also have the active significance for research in physical movement in deep earth, tectonic activities, plate movement and origin of life. Nowadays, subjects of marine science, geology and biology face the same mission of investigation of seafloor hydrothermal system. Upon the support of State 863 Program, a set of geochemical sensor with independent intellectual property containing reference electrode, pH electrode, H₂S electrode and dissoloved oxygen electrode is prepared for in-situ detecting on seafloor. It is useful to help people study hydrothermal system from geological, chemical, biological and other aspects, and thus greatly promote research in the field of sea resources detecting, sea environment observation and protection, and marine science.After studying in existing geochemical sensor and comparing previous preparation methods of these electrodes at home and aboard, the methods are taken as following: using noble metal as basic material, realizing the solidification and micromation of detecting electrodes; using AgCl melt to make reference electrode, enhancing its lifetime; using epoxy resin with ultra thin silver power as the middle layer to prepare Ag/Ag₂S electrode, enhancing its detecting limit; using Na₂O₂ melt to prepare Ir/IrO₂ electrode coated with Nafion, a kind of proton selective substance produced by DuPon, enhancing its resistance ability; using Au coated with DePeX membrane as DO electrode, enhancing its liftime and detecting ability. Constantly improve the electrodes performance by experimental calibrations according to the feedback.As a collaboration project between Zhejiang University and the University of Minnesota, a joint team has been working together on in-situ geochemical sensors for seafloor hydrothermal system. The device had been working continuously in a microbial cluster near TICA-vent for about 12 days and realized long-term chemical compositon monitoring for the first time in this area. Time-series records show that temperature fluctuates between 10°C and 20.5°C, and total dissolved varies from 7.4 to 27.3μmol/L. Through the analysing results of detecting data, it is found that temperature and chemical component concentration change periodically could be refered to tide influence.As a universal technical platform, in-situ geochemical sensor can be used widely. It has great potential applications in natural gas hydrate detecting, seabed observation system and other fields. Research results in this paper can reduce the gap in deep seafloor resources investigation technology between China and western countries and lay a sound foundation for deep-sea mineral resources investigation, exploration and exploitation.