Researchers conduct surveys on the Dead Zone (Hypoxic Zone) to report size fluctuations. (Photo: Nancy Rabalais/LUMCON/NOAA)
Mexican Gulf's dead zone smaller than expected: NOAA
Friday, August 05, 2011, 22:30 (GMT + 9)
Scientists from National Oceanic and Atmospheric Administration (NOAA) found the size of this year’s Gulf of Mexico dead zone is 6,765 sqmi. Researchers had predicted the potential for a record sized dead zone between 8,500-9,421 sqmi due to the spring flooding of the Mississippi River and the associated large loads of nutrients running off into the Gulf, but strong winds and waves associated with Tropical Storm Don disrupted the western portion of the dead zone.
The research cruise, led by Nancy Rabalais, PhD, executive director of the Louisiana University Marine Consortium, found this year’s dead zone to be nearly equal to the land area of the state of New Jersey.
The average size of the dead, or hypoxic, zone over the past five years has been 6,688 sqmi, very close to this year’s measurement and much larger than the 1,900 sqmi goal set by the Gulf of Mexico/Mississippi River Watershed Nutrient Task Force.
On the other hand, it has been stated that last year’s dead zone measured approximately 7,722 sqmi.
In addition to surveys in the traditional region of the dead zone, Rabalais’ research team documented a large area of hypoxia east of the Mississippi River in mid-July.
“Although Tropical Storm Don disrupted part of the hypoxic zone, our monitoring over the past several months indicated the spring floods had expanded the dead zone region,” said Rabalais.
“However, sampling the hypoxic bottom layer on a ship rolling in 6-10 ft waves presented safety and sampling issues that interfered with precise measurements at some stations. For these reasons, the size of the measured hypoxic zone was smaller than just before the storm, and is probably under-estimated,” she went on.
The dead zone 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.
“Despite fluctuations in size due to each year’s weather conditions, these chronic, recurring hypoxic zones every summer represent a significant threat to Gulf ecosystems,” said Robert Magnien, PhD, director of NOAA’s Centre for Sponsored Coastal Ocean Research. “Until we achieve a substantial reduction in nutrient pollution from the Mississippi River watershed, we will continue to experience extended periods of time each year when critically-needed habitat is unavailable for many marine organisms.”
Earlier this summer, NOAA-sponsored forecast models developed by R Eugene Turner, PhD, Louisiana State University and Donald Scavia, PhD, University of Michigan, predicted that the hypoxic zone would be the largest on record. Despite the presence of tropical storms, which can temporarily provide oxygen to bottom waters through mixing of the water column, the continued high discharge from the Mississippi River after the prediction provided strong conditions for a large dead zone.
Texas A&M will be conducting a NOAA-funded follow-up cruise in mid-August to provide an update on the size of the dead zone as scientists work to understand size fluctuations and duration of hypoxic conditions in the Gulf.
- Gulf of Mexico to suffer worst dead zone ever: NOAA