Washburn, who has been using radio waves to map ocean currents off Santa Barbara for a number of years, provided additional evidence. "Libe took a seven-year average of surface current flow in the region, and plotted that out," Valentine said. "It matched perfectly with our plume."
This research proved to be an extension of the 2008 study by Valentine and Reddy: that the oil has indeed degraded, largely eaten away by microbes, before it settles back to the ocean floor and becomes buried.
"For all of these samples, the bacteria seem to hit a common wall, where they don't eat anymore," Valentine said. "In the previous study, we were looking at subsurface biodegradation where there is no oxygen. Now, you still have thousands of compounds in that oil, but now we're seeing all of the evaporation and dissolution that happens to the slick, and then the biodegradation happens in the slick with oxygen present, and then when it falls to the sea floor, it continues to be biodegraded. All the oil seems to be biodegraded to the same point and then it just stops."
"It's dramatic how much the oil loses in this life cycle," Reddy said. "It's almost like someone who has lost 400 pounds."
It's the amount of residual oil that made it to the ocean floor that surprised all of the researchers. "Based on what we found in the sample cores at our sites, we calculated the amount of hydrocarbon in the whole area," Valentine said. "We have to make assumptions about how deep the sediment is, so we assume a range of between 50 centimeters and 5 meters. We come out with 8 to 80 Exxo
|Contact: George Foulsham|
University of California - Santa Barbara