NOAA: Average-sized ‘dead zone’ likely off Louisiana

NEW ORLEANS — An average “dead zone” is likely in the Gulf of Mexico, where a large area of water holding too little oxygen to keep marine animals alive forms every summer, the National Oceanic and Atmospheric Administration said Thursday.

A hurricane or tropical storm in the weeks before the July measurement cruise could shrink that considerably by stirring up the water and mixing in oxygen, NOAA noted.

It said its analysis of five university models indicates that this summer’s low-oxygen, or hypoxic, area will cover about 4,880 square miles (12,600 square kilometers).

That’s close to the five-year average of 5,400 square miles (14,000 square kilometers), NOAA said. It’s also bigger than the nation of Vanuatu, nearly double the size of the state of Delaware and 2.5 times a goal set in 2001 by the Gulf of Mexico Hypoxia Task Force.

The Mississippi River drains 40% of the continental Unite States, including all or part of 32 states.

The dead zone is created as calm weather lets water from the Big Muddy form a layer above the Gulf’s salt water, which is denser. Fertilizer and other nutrients carried downriver feed algae, which die and then decompose on the sea floor, using up oxygen from the bottom up. Fecal pellets from grazing zooplankton also contribute, said an analysis by the Louisiana Universities Marine Consortium’s Nancy Rabalais, who has been measuring the dead zone since 1985.