In addition to CTDs, core sampling and camera-tow operations, another aspect of our mission includes the mapping of natural hydrocarbon seeps in the vicinity of the Deepwater Horizon site.
The Pisces was designed to be used as a fisheries research vessel, and was outfitted with acoustic gear that is used for finding schools of fish. It uses sound, which refracts (or bends) when it passes between substances of different densities – such as between sea water and the air contained in the swim bladders of fish. Think of how a straw in a glass of water appears to bend at the water’s surface. This is due to the refraction of light waves as they pass between the air and the water. Sound waves work the same way.
This same equipment can also be used to find gases escaping from the sea floor. We spent the morning over a plateau in the ocean, very close to Mississippi Canyon, where the oil spill occurred. We made several passes back and forth over this plateau in a pattern that scientists sometimes call “mowing the lawn.” Scientists can see the returns from the acoustic equipment on computer monitors, where the seeps show up as vertical lines of dots.
Later on, once we had surveyed the entire plateau, the scientists were able to put the data together to create a three dimensional map of the seeps. Pretty cool, huh?