Midwest drought brings fourth smallest Gulf of Mexico 'Dead Zone' since 1985

A little ironic good cheer from NOAA: NOAA-supported scientists have found the size of this year’s Gulf of Mexico oxygen-free ‘dead zone’ to be the fourth smallest since mapping of the annual hypoxic, or oxygen-free area began in 1985. Measuring approximately 2,889 square miles, the 2012 area is slightly larger than Delaware.

The survey also found a patchy distribution of hypoxia across the Gulf differing from any previously recorded. This is in stark contrast to last year, when flood conditions, carrying large amounts of nutrients, resulted in a dead zone measuring 6,770 square miles, an area of the state of New Jersey. The last time the dead zone was this small was in 2000 when it measured 1,696 square miles, an area slightly smaller than Delaware.

“The smaller area was expected because of drought conditions and the fact that nutrient output into the Gulf this spring approached near the 80-year record low,” said Nancy Rabalais, Ph.D., executive director of the Louisiana Universities Marine Consortium (LUMCON) who led the survey cruise. “What wasn’t expected was how the scattered distribution of hypoxia areas differed from any others documented in the past. Confirmed, however, is the strong relationship between the size of the hypoxic zone and the amount of fresh water and nutrients carried to the Gulf by the Mississippi River.”

The smallest recorded dead zone to date measured 15 square miles in 1988. The largest dead zone, also called a hypoxic zone, measured to date occurred in 2002 encompassing more than 8,400 square miles. The average size of the dead zone over the past five years has been 5,684 square miles, more than twice the 1,900 square mile goal set by the Gulf of Mexico/Mississippi River Watershed Nutrient Task Force.

Hypoxia is fueled by nutrient runoff from agricultural and other human activities in the Mississippi River watershed, which stimulates an overgrowth of algae that sinks, decomposes and consumes most of the life-giving oxygen supply in bottom waters.

The hypoxic zone off the coast of Louisiana and Texas forms each summer and threatens valuable commercial and recreational Gulf fisheries. In 2010, the dockside value of commercial fisheries in the Gulf was $639 million. More than 4.6 million recreational fishers took an estimated 22 million fishing trips in 2010, further contributing to the Gulf economy."...

NASA image of sediment and runoff in the Gulf of Mexico