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Dauphin Island Sea Lab Scientists Report Drop in Oxygen on Alabama shelf

June 9, 2010

A Dauphin Island Sea Lab (DISL) project funded by the National Science Foundation Rapid Response initiative has documented a dramatic decline in dissolved oxygen near the ocean bottom at both 12 and 25 miles south of Dauphin Island, AL. Dr. Monty Graham, Senior Marine Scientist, DISL, said “Oxygen is dropping out offshore. We got minimum dissolved oxygen values of 1.7 mg/L and the hypoxic layer is about 3 m thick.” Graham leads the Fisheries Oceanography of Coastal Alabama group, which was funded by Alabama Governor Bob Riley in the aftermath of the liquefied natural gas (LNG) controversy.

Dissolved oxygen levels below 2 parts per million are considered dangerous for almost everything, plant or animal, that depends on oxygen for normal living. The values reported are less than 20% of normal levels. The animals that are able to leave these hypoxic areas will do so, but the less mobile can be killed at these exposures. There have been hypoxic areas reported from Alabama’s offshore in the past, but they were normally associated with old beach ridges south of Fort Morgan, not along this transect due south of Dauphin Island.

Any and all forms of organic material entering coastal waters contribute to oxygen consumption due to microbial activity. Discharge from local rivers can create the same kind of result. But this report does support the several findings from the academic vessels working in deeper waters offshore that have suggested that bacterial decomposition of the underwater plumes of dispersed oil is consuming large amounts of oxygen in this part of the Gulf of Mexico. Dr. George Crozier, Director of the Dauphin Island Sea Lab, said, “This is the kind of unexpected consequence that I warned BP representatives of on May 3rd, after they announced the successful application of dispersant at 5,000 feet.”

Crozier acknowledged the complexity resulting from the combination of harmful effects attributable to low oxygen levels with the issues surrounding the more obvious damage done by toxic components, which are contained in crude oil but are soluble in water. The interactions emphasize the absolute necessity for studying the Gulf of Mexico ecosystem as envisioned by Senator Richard Shelby and the National Marine Fisheries Service when they established the Shelby Center for Ecosystem-based Fisheries Management at the Dauphin Island Sea Lab three years ago.

There is growing concern within the scientific community that use of dispersants at depth may have trapped the toxic substances within the Gulf of Mexico where they threaten the existing populations and could pose a long-term issue for the food web upon which we sit at the top.




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