Ken Takai, Program Director of Subground Animalcule Retrieval (SUGAR) Program, Extremobiosphere Research Center (XBR: Dr. Kouki Horikoshi, Director-General), Japan Agency for Marine-Earth Science and Technology (JAMSTEC: Mr. Yasuhiro Kato, President) and his colleagues have discovered a blue hydrothermal emission ("Blue Smoker") at a depth of 1470 m at the Hatoma Knoll hydrothermal field in the Okinawa Trough (appendix), located at around 50 kilometers northwest off Ishigaki Island, Japan. It was found by onshore-analysis of the video image of the hydrothermal activity at Hatoma Knoll field obtained during the dive surveys using Manned Research Submersible "SHINKAI 6500". As far as we know, there has ever been no report on the blue hydrothermal emission. It is likely the world's first.
At the time, vigorous white hydrothermal emissions with numerous gas bubbles (White Smoker) have also been found in the field for the first time since the hydrothermal activity of the Hatoma hydrothermal field has been investigated in 1999, strongly suggesting the increased magmatic input into the hydrothermal activity.
The Hatoma Knoll is a submarine volcano located at around the volcanic arc-backarc system in Okinawa Trough. The hydrothermal activity of 200 meters in diameter has been discovered in 1999 inside the caldera, since then almost annually, the hydrothermal activity and its chemosynthetic ecosystem have been investigated and monitored mainly by XBR.
There is a lava dome in the center of this caldera and the biggest hydrothermal chimney in the seas around Japan (elevation more than 30 meters) is located in the middle. This chimney is called "Big Chimney", from top of which clear hydrothermal emissions (Clear Smoker) are observed. Many other Clear Smoker sites have been identified in the caldera but "Blue Smoker" was found only at the hydrothermal vent site approx. 10 meters north from Big Chimney.
Hydrothermal fluids at the Hatoma Knoll field are known to represent typical geochemical features commonly seen in other Okinawa Trough hydrothermal fields; particularly characterized by extremely abundant magmatic and organics-derived CO2 (e.g. Inagaki et al., PNAS, 103, 14164-14169, 2006), and extremely high concentration of potentially biogenic CH4 in the hydrothermal fluids but relatively less abundance of magmatic sulfur species such as H2S and S0.
The dive survey was conducted on August 3, 2006 at the hydrothermal field (1470 meters water depth) of the Hatoma Knoll in the southern Okinawa Trough using "SHINKAI 6500", and the hydrothermal emission was filmed. The film was analyzed onboard and the "Blue Smoker" and White Smokers were identified.
Although black-, gray-, white-colored (occasionally yellow-colored) and clear hydrothermal emissions have been encountered at the deep-sea hydrothermal floors, a blue hydrothermal emission has never been reported. For the reasons why "Blue Smoker" looks blue, we can present several possible explanations. For example, "silica colloid formation", and "ionization of iron, copper or other transition element" could be pointed to. Unfortunately we have not yet obtained the fluid samples from the "Blue Smoker", thus the mechanism is still unknown until further study will be done.
For the reason why "Blue Smoker" and White Smokers appeared suddenly at the Hatoma Knoll hydrothermal field, it might be strongly associated with the sudden increase of the magmatic volatile input into the hydrothermal fluids, particlarly H2S, S0 and sulfuric acid derived from thermal disproportionation of magmatic SO2, of which chemical mechanisms were previously demonstrated in the submarine volcanos in the western Pacific subduction zone (Gamo et al., Geology, 25, 139-142, 1997; Nakagawa et al., Environ Microbiol, 8, 37-49, 2006). Since it is known in the Mid Ocean Ridges that the epithodic change in magmatic input into hydrothermal fluids is closely related with the volcanic eruption and earthquake (magma activity) (Butterfield et al., JGR, 99, 4951-4968, 1994; Von Damm, AGU Monograph, 91, 222-247, 1995; Von Damm & Lilley, AGU monograph, 144, 245-268, 2004), the hydrothermal activity and geochemical variation at the Hatoma Knoll need to be monitored carefully for the future magmatic and seismic events. In particularly, the magmatic and seismic event-dependent change of hydrothermal fluid chemistry, endemic microbial and macrofaunal ecosystems is one of the hottest topics in Ocean Sciences (e.g., Tolstoy et al., Science, 314, 1920-1922, 2006) and such a research could be conducted in the Hatoma Knoll, of which geographyical and geological settings are quite different from the previous Mid Ocean Ridge systems.
In the additional research in March, we will sample a variety of hydrothermal fluids from "Blue Smoker" and White Smoker sites and will thoroughly analyze the fluid chemistry. We will also investigate the subseafloor microbial components responding to the sudden shift in hydrothermal fluid chemistry using our techniques (Takai et al., Extremophiles, 8, 269-282, 2004; Nakagawa et al., Environ Microbiol, 8, 37-49, 2006). Additionally, we will set up a monitoring system of the magmatic and seismic activity in the hatoma Knoll by installing ocean-bottom seismometer and other measuring instruments.
*1 silica colloid formation: The emission looks blue possibly because it contains silica particle (silica dioxide) that scattering short-length blue-color light.
*2 ionization of iron, copper or other transition element: When ionization of iron, copper or other transition element dissolved in water, coordinate bond complex with water molecules are formed. In this case, transition ion elements absorb lights except that of certain colors, so that the only remaining colors transmitted / reflected are visible. This time it's blue.