HR: 1340h
AN: B33A-1018 INVITED     [Abstracts]
TI: Fate of liquid CO2 discharged from the hydrothermal area in the Okinawa Trough
AU: * Shitashima, K
EM: shita@criepi.denken.or.jp
AF: Central Research Institute of Electric Power Industry, 1646, Abiko, Abiko, 270-1194 Japan
AU: Maeda, Y
EM: ymaeda@rite.dcc.co.jp
AF: CERES Inc., 1646, Abiko, Abiko, 270-1166 Japan
AB: Deep-sea hydrothermal systems are suitable for the on-site field analysis of a high CO2 environment in the ocean. Hydrothermal fluids are highly enriched in CO2 and show lower pH (about pH2-3) relative to seawater. The observation of the hydrothermal CO2 would provide the opportunity for understanding the physic-chemical behavior and diffusion process of CO2 in the ocean. Furthermore, the information on the hydrothermal ecosystem in the high CO2 environment is important for an environment impact assessment of the CO2 ocean sequestration. The observation of behavior of natural CO2 droplets (8-10?, 0.5ml) was carried out in the deep-sea hydrothermal system at the Okinawa Trough. The natural CO2 droplet contains CO2 of 95-98%, H2S of 2-3% and other gas species. The rising CO2 droplets were tracked by an ROV, and depth, temperature, salinity, pH and pCO2 in seawater near the CO2 droplets were measured during their ascent by using CTD and in-situ pH/pCO2 sensor. The behavior of the rising CO2 droplets was observed with an HDTV camera on an ROV. Mapping survey (400m X 400m, 3 layers) of low pH distribution was performed on the natural CO2 venting area by the grid navigation of the ROV that installed a pH/pCO2 sensor. The droplet size and the rise rate of CO2 droplets decreased during their ascent in water column (from 1470m to 900m depth). The CO2 droplets dissolved gradually and became small CO2 clathrate while rising, and the rising clathrate materials were found to disappear at 918m depth (552m above the bottom). Although the pH just above the sea floor CO2 vents showed pH 5, the pH depression in seawater surrounding the rising CO2 droplets was not observed. The results of pH mapping survey showed only localized pH depression at the CO2 venting site.
DE: 0330 Geochemical cycles (1030)
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0428 Carbon cycling (4806)
DE: 0450 Hydrothermal systems (1034, 3017, 3616, 4832, 8135, 8424)
DE: 4825 Geochemistry
SC: Biogeosciences [B]
MN: Fall Meeting 2005