文摘
In July 1999, we conducted a side-scan sonar survey in the southeastern Mediterranean Sea, between 300- and 800-m water depths approximately 30 nautical miles from the Sinai Peninsula and Gaza Strip. Examination of the sonar imagery revealed numerous acoustic targets, each on the order of a few meters and surrounded by small depressions. Subsequent visual inspection of two of these targets by a remotely operated vehicle (ROV) revealed they were cold hydrocarbon seeps through which small bubbles of gas and shimmering fluids were emitted. Surrounding each cold seep were benthic communities of organisms. The ROV was used to gather video and still-camera imagery, map the surrounding microbathymetry, and collect samples of the seep structure and associated organisms. A sub-bottom profiler, which was attached to the ROV, was used to image the submerged structure of the second seep site. Further examination and analysis revealed that the seeps comprise hard deposits of calcium carbonate, and that the organisms are clams and polychaetes which are probably chemosymbiotic. The origin of the seep gas is hypothesized to be the natural decay of organic matter in the sapropel sediment, leading to the production of methane. Circulating fluids, which carry the dissolved gas through preferential pathways along small faults or bedding planes, percolate through the seafloor, precipitate calcium carbonate, release gas, and support the benthic organisms.
