Mandy Joye: The methane concentrations in these plumes are 100 to 10,000 times as much as you would normally find in Gulf of Mexico water.

Mandy Joye is an oceanographer at the University of Georgia. In June 2010, Joye returned from an emergency research expedition in the Gulf of Mexico following the Deepwater Horizon oil spill. She talked to EarthSky about the high concentrations of methane gas she discovered in oil plumes deep beneath the surface of the Gulf of Mexico.

Mandy Joye: There’s also propane and butane, gases that derive from the same process of making oil.

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Dr. Joye said that there’s so much gas leaking into the Gulf that we might be looking at severe oxygen depletion in Gulf water. What happens, she explained, is that naturally occurring Gulf bacteria “eat up” the vast amounts of methane and other gases.

Mandy Joye: But in the process, they’re consuming molecular oxygen from the water. The reason that’s a problem is that you could potentially have large volumes of water floating around in the Gulf of Mexico that don’t have any oxygen.

Ocean life depends on oxygen. Oxygen depletion in the Gulf, Joye said, means lost habitat for wildlife, and potentially long-term repercussions on local fishing.

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Mandy Joye: The degradation of this oil and gas being injected in the gulf of Mexico is going to cause oxygen depletion in the water, there’s no way around it.

She explained that ocean plants like phytoplankton normally inject oxygen into marine systems, but the Gulf has been so chemically altered that even plants are having trouble surviving.

Mandy Joye: The microbial community is going to break this down, but it doesn’t come for free, it comes at the expense of the oxygen budget of the system, and that’s something that’s not easily corrected.

Joye said the this injection of gas is happening throughout the water column.

Mandy Joye: And the consumption of oxygen is happening throughout the water column. It’s not just in these plumes where you have high rates of microbial activity. We measure elevated rates of activity all throughout the water column. They were highest in the plumes, because that’s where the concentration of methane is the highest. But the whole water column is being stimulated by the oil and gas coming from the spill.

She said very little is known about the baseline methane cycle in the Gulf of Mexico, so there are many, many unknown surrounding the impact of the methane. She said that if scientists closely monitor the microbial activity and come to understand it, experts might be able to add an element (e.g., nitrogen) to speed of the breakdown of oil and dissolved gas.

Mandy Joye: I suspect that the microorganisms that live in the plumes are probably going to run out of some critical nutrient or oxygen. So their activity is going to be limited at some point. And these plumes are going to spread to other areas because you’re going to run out of some critical thing the bacteria need in the core of the plume.

Joye added that another science team affiliated with the University of Florida found a plume to the north of where she was working that spans 20 miles. She said other plumes likely exist, which means that large areas of the Gulf could be closed of to fishing for an indefinite period. Dr. Joye added that she does not believe dispersant, which was added to Gulf water by British Petroleum in an attempt to break up the oil, to be safe, because it has not been tested in open water at scale.