Qualified Good News on Subsea Dispersed Oil Plumes: Continued Low Oil Concentrations, No Dead Zones

Eli is a contributing correspondent for Science magazine.

A second report by a multiagency team of government and academic scientists, working on five research vessels between 19 May and 19 June finds the distribution of the plumes largely unchanged from the first analysis, released last month. "The report indicates that subsurface oil concentrations are highest near the wellhead and become more diffuse farther away from the source," says a press release.

But in 200 sets of samples, those concentrations were found to be only a few parts per million in the water, and only as far as 52 km from the wellhead. The big question, though, is what impacts that oil may be having on ecosystems. On that score, the report says explicitly that no ecological data was taken—they don't know yet what the undersea plume is doing to organisms or food webs. But the report offers one bit of hope.

Marine scientists have feared that the massive amounts of released oil and methane would feed microbes that in turn would consume available dissolved oxygen in large gulf regions, leading to hypoxia, or dead zones. But so far, the new report says, that hasn't occurred:

Dissolved oxygen levels are being continuously monitored as part of the EPA monitoring protocols required for the use of subsea dispersants. Dissolved oxygen measurements sometimes show a drop in dissolved oxygen at or below a depth of 1,000 meters, although these drops were not severe enough to indicate impending hypoxic conditions.

The report says that such minor drops may be a result of oil affecting the membrane of the detector the scientists were using; now scientists are using a second method to be sure.

Posted in Climate, Environment gulf oil spill, pil fate