 Study Area RADARSAT Imagery The RADARSAT subscene that Desmond Power and his colleagues at C-Core have provided clearly shows the R/V SEWARD JOHNSON positioned next to one of the natural oil slicks that originate from the oil and gas seeps we have been studying. To enhance visiblity, the SEWARD JOHNSON steamed to a point 5 nautical miles NW from our dive site and then returned at full speed, timing the transit to arrive at the dive site just as the satellite was overhead at 07:08 local time. The outgoing and return wakes are clearly visible cutting though the dark area of the slick. To the north and west of the vessel, you can make out numerous separate streams of oil that are arriving at the surface and drifting northward from individual vents on the bottom. What the satellite is seeing is practically invisible to the naked eye. The layer of oil is .1um thick across most of the area. It appears dark because the oil layer dampens the tiny capillary waves on the surface of relatively calm seas. This creates a "slick" that deflects the radar energy the satellite puts out. Backscatter from the surrounding non-oiled water reflects more radar energy back to the satellite and appears bright in contrast to the slick areas. Even though the floating oil layers are very thin, over time they represent a substantial volume of oil that dissolves and disperses into the ocean. Preliminary estimates suggest that natural seepage in the Gulf of Mexico returns between 0.5 to 1 x 10^8 l/y oil to the area. Interestingly, one result of this cruise has been to show the potential importance of gas in this process. The gas is invisible to the satellite, but helps the oil rise more quickly to the surface. The methane gas is itself a significant source of organic carbon in the Gulf. Methane is an important foodstuff for bacteria in seafloor sediments and in the water over seeps. Images COPYRIGHT 2002 Canadian Space Agency |