When oil sheen appeared on the sea surface last fall not far from the site of the Deepwater Horizon disaster in the Gulf of Mexico, authorities wanted to know where it was coming from.
Testing revealed that the oil slicks matched the Macondo crude. But seabed surveys showed the well cap was in good shape. Leaks were detected in the 39-foot-tall containment dome -- which contains an unknown quantity of oil -- but the sheen remained after the leaks were plugged.
Chemical sleuthing by scientists from the Woods Hole Oceanographic Institution and
Using a patented technique to test the sheen samples, researchers identified industrial lubricants used in the drilling process. While no drilling fluids were detected in samples from the dome leaks, samples from rig debris collected three years ago matched.
In a paper published online this week in the journal Environmental Science & Technology, the scientists concluded the likely sources of the slicks were rig tanks that held a mixture of drilling fluids and oil. As the 600-barrel tanks corrode on the gulf floor, the oil slowly escapes.