Some Of The Gulf Oil Underwater Plumes Are Not BP's

From "BP oil isn’t the only source of gulf's deep roaming plumes: Some subsea plumes don't share the chemistry of BP's oil" by Janet Raloff, ScienceNews Web edition, Wednesday, June 9th, 2010:

During a June 8 briefing for reporters, Steven Murawski, chief science advisor for the National Oceanic and Atmospheric Association’s Fisheries Service, described deep strata of water tainted with oil. They were identified during a recent cruise in the Gulf of Mexico. A presumption had been that any clouds of oil hovering under the surface would be plumes spewed by the damaged BP well head. But the chemical fingerprinting of diffuse undersea oil clouds at one sampling site 142 nautical miles southeast of the Deepwater Horizon accident site was “not consistent with BP oil,” he pointed out.

Which begs the question: Where did this other oil come from — since Murawski noted that earlier research surveys of the area prior to the BP spill had turned up no subsea oil clouds.