Development of a deep-sea hydrogen sulfide ion sensor and its application for submarine hydrothermal plume exploration

Abstract

A deep-sea hydrogen sulfide ion (HS^–) sensor was developed using electrochemical techniques for the direct measurement of hydrogen sulfide ion. In the sensor, linear sweep voltammetry is applied using three simple electrodes, Ag working electrode, Pt counter electrode and Ag/AgCl reference electrode. The measurement times are very small approximately 20 s. The sensor does not require an ion-selective membrane or chemical modification of the electrodes and are suitable for use in the deep-sea environment. In addition, the sensor is encased in a pressure-resistant container, and the electrodes have pressure adjustment functions. As a result, the sensor can withstand the temperature and pressure that exist up to 45°C and at water depths of 5000 m, respectively. With this sensor, it was possible to measure hydrogen sulfide ion levels with a detection limit of 2.2 μmol/L and a quantification range of 2.2–700 μmol/L. Field applications of the hydrothermal plume observations in the Mariana Trough and Okinawa Trough clarified the spatial distribution of hydrogen sulfide ion around the hydrothermal vents.