No "Dead Zone" In The Gulf
Oxygen levels in the Gulf are not low enough to create a ''dead zone''
These dissolved oxygen levels, measured within 60 miles of the wellhead, have stabilized and are not low enough to become "dead zones." A dead zone is an area of very low dissolved oxygen that cannot support most life. Dead zones are commonly observed in the nearshore waters of the western and northern Gulf of Mexico in summer, but not normally in the deep water layer (3,300 - 4,300 feet) where the lowered oxygen areas in this study occurred. Dead zones, also known as hypoxic areas, are defined in marine waters as areas in which dissolved oxygen concentrations are below 2 mg/L (1.4 ml/L).
"All the scientists working in the Gulf have been carefully watching dissolved oxygen levels because excess carbon in the system might lead to a dead zone. While we saw a decrease in oxygen, we are not seeing a continued downward trend over time," said Steve Murawski, Ph.D., NOAA's Chief Scientist for Fisheries and the head of the Joint Analysis Group. "None of the dissolved oxygen readings have approached the levels associated with a dead zone and as the oil continues to diffuse and degrade, hypoxia becomes less of a threat."
Since the Deepwater Horizon incident began, EPA and NOAA have systematically monitored dissolved oxygen levels along with other parameters from the sea surface to about 5,000 feet deep near the spill site. Data from 419 locations sampled on multiple expeditions by nine ships - NOAA Ships Gordon Gunter, Henry Bigelow, Nancy Foster and Thomas Jefferson and the research vessels Brooks McCall, Ferrel, Jack Fitz, Ocean Veritas and Walton Smith - over a three-month period, were analyzed for this report.
The JAG report does not specifically address the question of the rate of biodegradation of oil.