Our findings indicate the presence of a continuous plume over 35 km in length, at approximately 1100 m depth that persisted for months without substantial biodegradation. Samples collected from within the plume reveal monoaromatic1 petroleum hydrocarbon concentrations in excess of 50 µg L–1.These data indicate that monoaromatic input to this plume was at least 5500 kg day–1, which is more than double the total source rate of all natural seeps of the monoaromatic petroleum hydrocarbons in the northern Gulf of Mexico. Dissolved oxygen concentrations suggest that microbial respiration rates within the plume were not appreciably more than 1 µM O2 day–1
1Having a closed ring of alternate single and double bonds; derivatives of the hydrocarbon benzene.The existence of underwater plumes of oil has been posited by Jean-Michel Cousteau and a team of Woods Hole research scientists. Meanwhile, federal officials have downplayed the idea of underwater oil plumes.
Major study proves oil plume that's not going away - Yahoo! News
Using instruments like the underwater mass spectrometer to detect the unique signature from the BP oil spill, the Woods Hole scientists mapped a plume that was more than a mile wide and more than 650 feet from top to bottom. The plume is probably more than 22 miles long, but scientists had to stop measuring because of Hurricane Alex.
Recently, federal officials have admitted that as much as 42 million gallons of oil may be lurking below the surface. NOAA, the federal agency, redirected much of its sampling for underwater oil after consulting with Woods Hole researchers.
High concentrations of oil are acutely toxic, but low concentrations have more subtle, widespread effects. As oil percolates through food webs, it retards plant and animal growth, leaving them vulnerable to predation and disease, and less fit to reproduce.
Why are their plumes of oil? Three reasons: the massive amount of oil leaked from the bottom of the Gulf, the cold of the deep water in the Gulf inhibiting oil degradation and the use of dispersants at the well head keep oil from rising to the surface.