In response to a need to map the chemosynthetic communities, Carbonate rock outcrops and active gas vents at the MC 118 site for the Sea Floor Observatory and related scientific missions planned for this site, SDI undertook the design and construction of a system to map and provide in real time to the surface ship images and positions of the sea floor features. This system, dubbed “Deep See” utilized the fiber optic equipped lift cable for the SFO Station Service Device (SSD) along with many of the pieces planned for installation into the SSD.
Deep See System
The Deep See included a deep ocean video inspection framework with the main communications and control computer system and the fiber optic capabilities of the armored cable on the R/V Pelican’s winch. This provided a command and control capability for two way, multiple cannel, high data rate communications over the fiber in this cable. A shipboard computer and software program controls acquisition of multiple video channels, Ethernet communications, multiple serial channels and high speed back link between the Station Service Device command and control unit and the computer on the ship. The Deep See included a high resolution low light color video camera, two deep ocean underwater lights, and an altimeter (Fig. 4). A pressure compensated junction box from the Station Service Device allowed interfacing the components on Deep See. Also installed on Deep See were mounts for an acoustic release and a core tube. Power for Deep See was provided by modifying pressure compensated battery packs with newly installed AGM batteries. Dual battery mounts allow quick replacement of batteries for minimal down time when the battery pack runs down. The ballast weights were made to be easily redistributed to compensate for different payloads and battery pack locations. The USBL was mounted on the Deep See and the position of the USBL and Deep See were integrated into the video record providing accurate real time positioning of the seafloor in the video records.
Field Operations
Following a 1 ½ month design and build cycle, the Deep See was put to immediate use on its first deployment. The real time, video reconnaissance survey of the MC 188 GOM SFO site was conducted in two separate deployments totaling approximately 18 hours. The equipment operated nearly flawlessly and close to ten hours of video was captured on DVD and VHS tape. The best images were obtained while maintaining a one to two meter altitude. Plans to add a surge arrester will aid in holding a set altitude. Latitude, Longitude, heading, time and date are captured on each frame of the video for future reference.
The survey was conducted using an SDI and HYPACK navigational system with AUV acquired bathymetry imported as a base image. Ship and Deep See positions were plotted in real time on the image using GPS and USBL locators, respectively. Sites of interest were plotted and then the captain positioned the ship to slowly motor over these areas. The captain maintained a speed of approximately 1.5 knots and had to take currents and wind into consideration when trying to cross a targeted area. Slow “drift” speeds and currents required a non-regular survey pattern with the captain having to use his best judgment on how to maneuver the ship to the points of interest.
Areas of interest for the survey concentrated on the three suspected vent areas at the site and, to a lesser extent, the areas of high backscatter identified by a previous AUV side scan sonar survey of the site. Approximately 16 traverses were made across the site in attempts to drift over the targeted areas. The survey paths vary one from the other as the captain tried to read the currents, ship speed, and target locations with each pass across the hydrate mound. Areas of Authigenic carbonate rocks, bacterial mats, shell beds and gorgonian corals were present in different areas around and in the crater like structures of the vents. Some gaseous discharge was also observed and more is suspected to be identified upon review of the data. Screen captures of various features are presented below (Figures 4-6). An edited version of one to two hours in length of highlighted areas of the data is expected to be developed and made available for distribution to interested Gulf of Mexico Hydrates research Consortium members.
Sediment Temperature Gradient Monitoring
Early indications of first data recovered from the SFO During the September 2006 cruise. Two months of thermal gradient data from the GPA array was recovered during last weeks cruise. This data includes 0.01 degree C accuracy and 0.001 degree resolution of temperature of bottom water and sediment temperatures at 1 meter below the surface and 4 meters below the surface. This thermal gradient data was taken hourly and more than 2 months of data has been recovered. The early review of this data shows some time periods of 0.2 degrees C diurnal variations with approximately 3 hour delay to correlated variations of 0.1 degrees C in the 1 meter sediment depth. The 4 meter sediment temperatures appear to be stable within 0.003 degrees and show a loose correlation to long term trends in surface waters. There are several events which represent exceptions to the correlation of the sediment temperature with the bottom water temperatures. These could indicate dissociation of Gas Hydrate or be representative of gas venting. The source of the diurnal variation in bottom water is not known and will warrant further investigation. This data represents new capabilities in long term temperature measurements and the accuracy and resolution of these measurements.