2012 Expedition of Hydrothermal Vent Fields in Tonga Arc by KORDI

Abstract

To understand the environmental characteristics of potential mining sites for the massive sulfide deposits in Tonga Arc, the environmental baseline studies were carried out from Jan. to Feb. of 2012, focusing on two hydrothermal vent sites located in the Tongan water. We investigated vent environments with chemical, geological and biological samplings using a ROV system (ROPOS). The ROV survey was focused on the visual observation of target vent sites with collection of plume water, vent fauna and sediments. Temperature, salinity, pressure (or depth), dissolved oxygen (DO) and carbon dioxide (pCO2) data were also collected simultaneously by sensors mounted on the ROV. The temperature and pCO2 increased at the vent sites, particularly pCO2 reached more than 1000 uatom at the site of mass of dead (or‘inactive’) chimneys. The data obtained from ROV sensors well agrees with visual observation by mounted HD camera. Hydrological and chemical properties of water column above the vent sites were also investigated with CTD castings with DO and pH sensors and LADCP (Lowered Acoustic Doppler Current Profiler). In addition, short- and long-term ADCP moorings and sediment traps were operated at the selected locations near the vents. Performed environmental sampling and analysis in this study are based on the recommendation and documents by ISA.