09:30 〜 09:45
[S24-2-05] Long-term observations of pressure, temperature and flow rate for deep-sea hydrothermal fluid at the middle Okinawa Trough
The middle Okinawa Trough locating along the Ryukyu-arc has several active seafloor hydrothermal fields. Cruise CK16-01 by D/V Chikyu targeted the Iheya-North and Noho hydrothermal fields to comprehend sub-seafloor geological structure and polymetallic mineralization. In this cruise, we installed the Kuroko cultivation apparatus that can monitor fluid pressure, temperature and flow rate of the artificial hydrothermal vent.
In February 2016 during Cruise CK16-01, two Kuroko cultivation apparatuses equipped with P/T sensor, flowmeter and load cell were installed at Holes C9017B and C9024A. In January 2017 during Cruise KR16-17 , two cultivation cell parts including sensors were recovered by ROV Kaiko Mk-IV and R/V Kairei . In this study, we report long monitoring data of hydrothermal fluid for more than 10 months at two deep-sea artificial hydrothermal vents.
Hole C9017B at the Noho site, fluid temperature was constant for 5 months from the beginning of the cell deployment. Then, temperature became decreasing from 75 to 40oC gradually. The day and monthly periodic transition of temperature (the amplitude was ca. 0.3 - 0.5oC) induced by tidal wave was found. Among such periodicity, high temperature peaks coincided with low pressure peaks. Drilling operation at Hole C9017A which is 10 m away from Hole C9017B during Cruise CK16-05 in November 2016 would have influenced subseafloor hydrology and induced sudden temperature and pressure drops.
Hole C9024A at the Iheya-North site, pressure, temperature and flow rate also changed periodically with tidal wave, and maximal and minimal points of flow rate were concurrent with those of temperature. The maximum temperature reached 308oC, which is similar to the value obtained from the ROV thermometer (311oC) at the Iheya-North field. The average flow rate of hydrothermal fluid was ca. 300 L/min and, 9 days later, flow rate became zero, suggesting that the impermeable minerals sealed top of the cultivation apparatus.
In February 2016 during Cruise CK16-01, two Kuroko cultivation apparatuses equipped with P/T sensor, flowmeter and load cell were installed at Holes C9017B and C9024A. In January 2017 during Cruise KR16-17 , two cultivation cell parts including sensors were recovered by ROV Kaiko Mk-IV and R/V Kairei . In this study, we report long monitoring data of hydrothermal fluid for more than 10 months at two deep-sea artificial hydrothermal vents.
Hole C9017B at the Noho site, fluid temperature was constant for 5 months from the beginning of the cell deployment. Then, temperature became decreasing from 75 to 40oC gradually. The day and monthly periodic transition of temperature (the amplitude was ca. 0.3 - 0.5oC) induced by tidal wave was found. Among such periodicity, high temperature peaks coincided with low pressure peaks. Drilling operation at Hole C9017A which is 10 m away from Hole C9017B during Cruise CK16-05 in November 2016 would have influenced subseafloor hydrology and induced sudden temperature and pressure drops.
Hole C9024A at the Iheya-North site, pressure, temperature and flow rate also changed periodically with tidal wave, and maximal and minimal points of flow rate were concurrent with those of temperature. The maximum temperature reached 308oC, which is similar to the value obtained from the ROV thermometer (311oC) at the Iheya-North field. The average flow rate of hydrothermal fluid was ca. 300 L/min and, 9 days later, flow rate became zero, suggesting that the impermeable minerals sealed top of the cultivation apparatus.