An unusual low oxygen zone in Gulf of Mexico waters off the Alabama shore has persisted for more than a month, and evidence points to the ongoing Deepwater Horizon oil spill as the cause.
Oil spills can deplete oxygen in water by providing a source of food to microbes that grow on oil and consume oxygen in the process.
Researchers can’t say how low oxygen levels will affect the region’s ecosystem in the long term, but for now, most animals that can swim away have left the area. Plankton in the zone have died.
The researchers measured low oxygen levels along the entire 40-mile stretch they sampled around Dauphin Island, Ala., from about 40 miles offshore to within a mile or two of the shoreline. The bottom layer of water was oxygen-depleted at depths of about 30 feet close to shore to 100 feet further out, along the continental shelf — a rim of shallow water tracing the coast from Mississippi to Florida.
“It’s not little local pockets,” said Monty Graham of the Dauphin Island Sea Lab, who is tracking the zone. “It’s over a regional scale. It wouldn’t surprise me if there were a band of low oxygen over that entire area between the Mississippi River and Apalachicola, Florida.”
“The low oxygen was pushing up very close to the shore,” he added.
His team trawled the waters to survey wildlife.