Hydrocarbon hemorrhage

By

Lisa Duchene, SeafoodSource contributing editor

Published on
July 13, 2010

I am obsessed with the Gulf of Mexico disaster. I refuse to call it an oil spill. For one, “spill” is far too benign. You take a “spill” on your bicycle, and might say “oops.” This event is not an “oops.” It is a manmade disaster, a tragedy of unprecedented scale.

For now, I’m going with “hydrocarbon hemorrhage” — albeit not a headline-friendly term. But it’s pretty accurate, because of what has actually been spewing into the Gulf and what it means.

Let me explain.

Samantha Joye is an oceanographer at the University of Georgia in Athens, Ga., who researches microbial processes and naturally occurring gas and oil seeps in the Gulf. “This is a hydrocarbon spill,” she said in a press briefing on Tuesday.

Of the reservoir tapped by the Deepwater Horizon rig and still spewing into the Gulf — Tuesday was Day 85 — gas makes up 40 percent of the hydrocarbons. Most of that gas is methane.

We’ve all seen the grotesque images of sticky, ugly black oil and tarballs that turn up on beaches and assault helpless birds and sea turtles. What we can’t see so well is the invisible methane quietly sucking oxygen from the water. The result is areas of low oxygen in the Gulf, over an unknown area, to an unknown degree, for an unknown length of time. Low-oxygen zones are not places fish wish to live. The less Gulf habitat impacted, the better.

Joye does not foresee the entire Gulf turning into an anoxic, or severely low-oxygen, “dead zone.” “The whole basin is not going to be an anoxic basin,” she said. That’s a relief. Fisheries scientists are saying that while no one knows the future for Gulf fisheries, they are optimistic we’ll see declines, not wipeouts, of year-classes and populations, all depending on how fish and their larvae react to the toxicity of crude and their habitat.

When Joye testified on 9 June before the congressional committee on energy and the environment, she explained the Gulf’s natural response to hydrocarbons: “Because the Gulf of Mexico experiences natural seepage, the natural microbial community here is poised to consume oil and gas. At least 1,000 naturally occurring seeps along the Gulf of Mexico shelf and slope deliver from 1,000 to 2,000 barrels of oil per day into the Gulf’s waters. However, the magnitude of this spill may saturate the microbial community’s ability to consume the introduced oil and gas.”

On Tuesday, Joye reported results of her sampling for methane-eating microbes from within the sub-surface plume of oil and gas: numbers of microbes doubled in a 24-hour period. They are “very big, fat happy cells that look a lot like methane-oxidizing or methane-eating bacteria,” she said. “The fact that it doubled is jaw-dropping. Clearly the microbial community is responding rapidly and rigorously to the input of oil and gas.”

The good news is the natural system has gone to work, feasting on methane. The bad news is that process draws oxygen from the water. In fact, when oxygen levels fall too low, microbial growth slows.

Joye explained that the gas is concentrated in layers, not found throughout the water column. That means there could be deep layers of low-oxygen water that impact the shelf and bottom organisms and fish. “The extent of which I don’t think we can even begin to pretend we understand at this point in terms of how large in scale they might be,” she said.

But, gratefully, not so big they threaten the entire Gulf. Watching this entire event play out is both scary — and fascinating. It’s been two weeks since I returned from a trip to New Orleans, but my head and heart are still there.

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