On its first voyage using the Kongsberg multibeam echosounder EM 302, the NOAA ship Okeanos Explorer made a major discovery of what are believed to be methane gas plumes.
EM 302 water column data detected the plumes while transiting to the Cordell Bank National Marine Sanctuary working grounds from Astoria, Oregon. The plumes were located in water depths between 1200 and 1900 meters. All plumes were observed to rise to a water depth between 500-550 meters making their heights between 700-1400 meters. In a journal article about the findings, Dr. Gardner and Mashoor Malik (CCOM/JHC) report that although seafloor sediments in shallow areas closer to the coast are known to harbour methane, no one has reported such plumes in waters this deep.
A potent greenhouse gas
The discovery of methane, a potent greenhouse gas, is very significant for marine life. Scientists fear that as the world's oceans warm, huge amounts of methane will be released. This will increases the acidity of the ocean, and can inhibit the ability of marine creatures to grow shells. Dr. Jim Gardner and Mashoor Malik (CCOM/JHC) suggest that the plumes are made up of a stream of methane bubbles coated with methane-rich ice which will melt as a result of warmer waters.
"The ice coating, a material called methane hydrate, is stable in deep water, where pressure is high and the water is cold. When the ice-cloaked bubbles ascend into warmer waters near the surface, the ice melts and the methane dissolves into the sea", they report.
High resolution maps
Okeanos Explorer is the only United States ship assigned to exploring systematically our largely unknown ocean. It is fitted with a hull-mounted, first of its kind, Kongsberg EM 302, which will provide explorers with high-resolution maps of the seafloor from 40 to 4000 meters. Maps from the system will be used to identify unique seafloor features for further exploration, and will be integrated into the high-precision DVL-Nav navigation system to provide a road map for exploring a particular site with the ROV.
Four more Kongsberg orders
The National Oceanic Atmospheric Administration (NOAA) operates a wide assortment of hydrographic survey, oceanographic research, and fisheries research vessels. After a recent ordered of four more Kongsberg hydrographic mMultibeam systems, including an EM 122 (1x1 Degree) for the ship Ronald H. Brown and an EM 710 (0.5x1 Degree) for the ship Rainer, NOAA now has a full suite of Kongsberg multibeams.